animal reproduction essay

• About Organismal Biology
• Phylogenetic Trees and Geologic Time
• Prokaryotes: Bacteria & Archaea
• Eukaryotes and their Origins
• Land Plants
• Animals: Invertebrates
• Animals: Vertebrates
• The Tree of Life over Geologic Time
• Mass Extinctions and Climate Variability
• Multicellularity, Development, and Reproduction
• Animal Reproductive Strategies

Animal Reproductive Structures and Functions

• Animal Development I: Fertilization & Cleavage
• Animal Development II: Gastrulation & Organogenesis
• Plant Reproduction
• Plant Development I: Tissue differentiation and function
• Plant Development II: Primary and Secondary Growth
• Principles of Chemical Signaling and Communication by Microbes
• Animal Hormones
• Plant Hormones and Sensory Systems
• Nervous Systems
• Animal Sensory Systems
• Motor proteins and muscles
• Motor units and skeletal systems
• Nutrient Needs and Adaptations
• Nutrient Acquisition by Plants
• Water Transport in Plants: Xylem
• Sugar Transport in Plants: Phloem
• Nutrient Acquisition by Animals
• Animal Gas Exchange and Transport
• Animal Circulatory Systems
• The Mammalian Cardiac Cycle
• Ion and Water Regulation and Nitrogenous Wastes in Animals
• The Mammalian Kidney: How Nephrons Perform Osmoregulation
• Plant and Animal Responses to the Environment

Learning Objectives

• Identify and describe functions of key anatomical reproductive structures present in various types of animals, including the spermatheca, the cloaca, the ovary and related structures, and the testes and related structures
• Compare and contrast the process, products, and locations of male and female gametogenesis in mammals
• Describe roles of hormones in gametogenesis (spermatogenesis and oogenesis), ovulation, and implantation in placental mammals
• Explain how various medical interventions affect reproductive cycles and fertilization

Diversity of Animal Reproductive Anatomy

The information below was adapted from OpenStax Biology43.2

Many animal reproductive structures are very similar, even across different lineages. Reproductive structures produce gametes (eggs and sperm) and facilitate the meeting of gametes to produce a zygote (fertilized egg). In animals ranging from insects to humans, males produce  sperm  in  testes,  and the sperm are stored in the  epididymis  until ejaculation. Sperm are small, mobile, “low-cost” cells that are produced in high numbers. Females produce one  ovum  or several ova (eggs) that mature in the  ovary . Eggs are large cells that require a substantial investment of time, energy, and nutrients to form, are non-mobile, and are rare relative to sperm numbers. Mature eggs are released from the ovary into the uterine tubes (aka fallopian tubes or oviducts) where they are either fertilized (animals that reproduce via internal fertilization), or are released in an aqueous environment (animals that reproduce via external fertilization).

The first half of Hank Green’s video below has a nice summary of these and other ideas we’ve discussed previously, and the second half introduces human reproductive anatomy before we take a deep dive into the structures and functions via dynamic hormonal regulation:

For sexually reproducing populations, we can biologically define females as the sex with ovaries that produce small numbers of large eggs, which subsequently travel down a uterine tube; and males as the sex with testes that produce large numbers of small sperm, stored in an epididymis. While this general anatomy holds true, here are some interesting differences in different animal lineages:

• Spermatheca: The spermatheca is a specialized sperm-storing sac present in females in some invertebrate species. Spermatheca are common in many insects, some mollusks, and some worms. After mating, the female stores the male’s sperm in the spermatheca for later use, sometimes up to a year or more. Fertilization can then be timed with environmental or food conditions that are optimal for offspring survival. Sperm may be stored from one male or from multiple males, depending on the species mating system. In some species, the female may mate only once in her lifetime, and use the sperm from this single mating to fertilize eggs throughout her life.
• Cloaca: The cloaca is a single, shared body opening that functions in the digestive, excretory (urine), and reproductive systems. Cloacas are found among many non-mammal vertebrates, such as most birds and reptiles. Mating between birds or reptiles usually involves positioning the cloaca openings opposite each other for transfer of sperm from male to female. Ducks are a rare exception, where the males have a penis.
• Uterus: The uterus is a structure present in placental mammals (not all mammals have a uterus!) which houses the developing offspring internal to the mother’s body. The uterus essentially is location for development of an amniotic egg that is not laid outside of the body. Depending on the species, the uterus may have two chambers in species that produce multiple offspring at a time (such as mice), or only one chamber in species that produce one offspring, (such as primates).

Mammalian (Human) Reproductive Anatomy, Gametogenesis, and Hormonal Regulation

The information below was adapted from OpenStax Biology 43.3

The remainder of this reading will focus on mammalian reproduction, featuring humans as a model organism. We’ll first look at females and then males, emphasizing the structures, the process of gametogenesis, and hormonal control of reproduction.

Gametogenesis is the production of gametes, or sperm and eggs. Gametogenesis requires meiosis (see the Biological Principles textbook page on  Cell Division  for help with this often confusing concept). Meiosis produces haploid cells with half the number of chromosomes normally found in diploid cells.

Hormones regulate gametogenesis in both male and female reproductive cycles, including some of the same hormones. For example, follicle stimulating hormone (FSH)  and  luteinizing hormone (LH)  are named after their functions in egg production in females, but they play important roles in sperm production in males as well.

Human Female Reproductive Anatomy

Human female reproductive structures include both external and internal structures. External structures include the breasts and the vulva. Internal structures include ovaries, oviducts, the uterus, and the vagina, shown below.

This table briefly  summarizes the major organs, locations, and functions of mammalian female reproductive anatomy:

Humans females become capable of reproduction at sexual maturity, which follows puberty. During puberty, the hypothalamus in the brain signals the pituitary gland to produce two hormones, follicle-stimulating hormone  ( FSH ) and  luteinizing hormone  ( LH ). In females, FSH and LH stimulate the ovaries to produce the female sex hormones, estrogen and progesterone. During puberty, these hormones initiate development of secondary sex characteristics (such as breasts) and cause the ovaries to begin producing mature eggs.

Ovaries  are the site of egg development and maturation. Eggs develop and mature in structures called follicles , which are found throughout the ovary. Each follicle contains one immature egg. Egg development in humans occurs in small batches, with one or two eggs maturing on an approximately-monthly cycle called the ovarian cycle :

• In the first phase of the ovarian cycle, the several follicles become activated to promote development of the egg inside of them (recall that each follicle contains one immature egg).
• At the middle of the ovarian cycle, the most mature follicle will “rupture,” releasing one egg as illustrated below (rarely, a second follicle will rupture, resulting in ovulation of two eggs). The egg travels from the ruptured follicle into the oviducts (also called fallopian tubes ), where it will be fertilized if sperm are present. Over the course of about a week, the egg will travel through the oviduct into the uterus, where it will implant and result in pregnancy if fertilization previously occurred in the oviduct. Fertilization must take place in the oviduct, not the uterus.
• In the last phase of the ovarian cycle, the ruptured follicle (still in the ovary) becomes the corpus luteum , which secretes hormones that prevent menstruation until the egg has had time to be fertilized. If fertilization and implantation in the uterine wall occurs, then the corpus luteum continues to prevent menstruation; if fertilization does not occur, then the corpus luteum degenerates and menstruation occurs.

Female Gametogenesis: Oogenesis

Now that we have discussed the human female reproductive structures, let’s walk through the process of oogenesis , or egg production.

The process of oogenesis begins while the female herself is still an embryo! Oogenesis occurs in the the ovaries, where egg stem cells, called oogonia , divide by mitosis to produce up to 2 million oocytes (a precursor to the egg). The oocytes start the process of meiosis, and then pause during meiosis I. This process occurs during embryonic development, meaning that a female mammal is born with every single egg she will be able produce during her lifetime already present (in an immature form) in her ovaries. This situation is very different from males, whose spermatogonia (the sperm equivalent to oogonia) do not begin producing spermatocytes (the sperm equivalent to oocytes) until puberty.

The oocytes remain paused in meiosis I until the onset of puberty, when a series of events can lead to egg maturation on an approximately monthly basis:

• Hormones from the pituitary cause some of the follicles to begin developing and the oocyte inside the follicle to finish meiosis I (recall that each follicle contains one immature egg).
• After completing meiosis I, the oocyte pauses during meiosis II.
• Though several follicles are activated during each cycle, typically only one follicle will release an oocyte. The released oocyte will begin traveling through the oviduct, still paused in meiosis II.
• If the oocyte is fertilized by a sperm cell, it will finish meiosis II to produce a single fertilized egg (a zygote). If it is not fertilized, the oocyte degrades without completing meiosis II.

One final point: when each oocyte undergoes meiosis to go from diploid to haploid, each oocyte produces only a single egg (this is different from spermatogenesis, which produces four sperm from each spermatocyte). The oocyte undergoes a process called unequal cytokinesis , meaning it divides unequally so that almost all of the cytoplasm goes into only one daughter cell rather than evenly distributed into both. The smaller cell is called a polar body, and it normally dies as development progresses.

The process of oogenesis is illustrated below:

Hormonal Control of Oogenesis

Now that we have discussed the structures and the processes of oogenesis, we’ll move into the most complex part: hormonal regulation of oogenesis. Oogenesis is directly controlled by four hormones: follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone, and estrogen. These hormones together regulate the ovarian and menstrual cycles . The ovarian cycle refers to the release of eggs, and the menstrual cycle refers to activities in the uterine lining in preparation for possible pregnancy. We will focus only on the ovarian cycle in this course.

We’ll start with a brief overview of the roles the hormones play:

• Follicle stimulating hormone (FSH)  activates follicles within the ovary to promote development of egg cells, causing eggs to finish meiosis I and pause during meiosis II. (Recall that each follicle contains one immature egg cell which was paused in meiosis I.)
• Luteinizing Hormone (LH)  promotes release of the most mature egg (or in rare cases, eggs), resulting in ovulation
• Progesterone suppresses release of more FSH or LH to block activation of new follicles, allowing time for the ovulated egg to be fertilized in the oviduct and then travel to the uterus where it will implant if previously fertilized.
• Estrogen  can be thought of as an ‘enhancer’ in the ovarian cycle; it enhances the activation of follicles in response to FSH, and it also enhances suppression of follicles in response to progesterone. (Estrogen also has other roles outside of the ovarian cycle, including re-growing the lining of the uterus following menstruation, and it is responsible for the secondary sexual characteristics of females such as breast development.)

Now we’ll integrate the hormone activities into the three phases of the ovarian cycle. The ovarian cycle lasts approximately 28 days on average:

Follicular phase: The first half of the ovarian cycle is the  follicular phase , named for the fact that the dominant feature is the activated follicles.

• During this phase, FSH is being released from the pituitary in the brain. The slowly rising levels of FSH prompt the follicles on the surface of the ovary to grow and begin maturing the egg inside for ovulation.
• As the follicles grow, they release estrogens. Estrogens enhance the effects of FSH. The more the follicles grow, the more estrogen they release; the increasing estrogen levels cause a positive feedback loop promoting more follicle growth, which in turn promotes more estrogen release.
• Within each follicle, the maturing egg finishes meiosis I (recall that the eggs began meiosis I while the female herself was an embryo), and then pauses again during meiosis II.

Ovulation  occurs near the middle of the cycle (approximately day 14), when the high level of estrogen (produced by the developing follicles) causes a rapid rise and sharp spike in levels of LH and FSH to a lesser degree (both released from the pituitary in the brain).

• The spike in LH causes ovulation: one of the mature follicles ruptures and releases its egg (still paused in meiosis II). The other mature follicles will degenerate, and their eggs are lost.
• LH and FSH levels fall immediately after ovulation, and the level of estrogen decreases when the extra follicles degenerate.
• It takes about seven days for an egg to travel through through the oviduct from the ovary to the uterus, and it must be fertilized while in the oviduct. If the egg is fertilized, it will complete meiosis II, producing a single mature (and fertilized) egg.

Luteal phase: Following ovulation, the ovarian cycle enters its  luteal phase , named for the fact that the dominant feature is the corpus luteum , the structure the remains from the ruptured follicle.

• During this phase, the corpus luteum produces progesterone and estrogen. The progesterone inhibits the release of further FSH or LH, suppressing activation of any new follicles. The uterus becomes prepared to accept a fertilized egg, should fertilization occur.
• The inhibition of FSH and LH by progesterone prevents any further eggs and follicles from developing. The level of estrogen produced by the corpus luteum increases to a steady level for the next few days; estrogen enhances the effects of progesterone.

What happens next depends on whether the egg was fertilized while it was in the oviduct:

• If a fertilized egg does implant in the endometrial lining of the uterine wall, then embryo produces a hormone called human chorionic gonadotropin (hCG). hCG causes the corpus luteum to remain instead of degrading, which in turn causes the ovary to continue producing high levels of progesterone. The progesterone prevents initiation of another ovarian cycle during the pregnancy. (The placenta takes over this process later in pregnancy.) Because hCG is unique to pregnancy, it is the hormone detected by pregnancy tests.

The figure below visually compares the ovarian and uterine cycles as well as the hormone levels controlling these cycles.

This video provides a great overview of the human female reproductive system, emphasizing many of the points described above:

Human Male Reproductive Anatomy

As with females, human male reproductive structures include both external and internal structures. External structures include the testicles or testes (singular: testis) and the penis. Internal structures include the vas deferens, the seminal vesicles, the prostate gland, and the bulbourethral gland.

This table briefly  summarizes the major organs, locations, and functions of mammalian male reproductive anatomy:

Humans males become capable of reproduction at sexual maturity, which follows puberty. During puberty, the hypothalamus in the brain signals the pituitary gland to produce two hormones,  follicle-stimulating hormone  ( FSH ) and  luteinizing hormone  ( LH ). In males, FSH and LH stimulate the testes to produce sperm and the male sex hormone, testosterone. During puberty, these hormones together initiate development of secondary sex characteristics (such as larger penis and testes, and deeper voice) and cause the testes to begin producing mature sperm.

The scrotum houses the testes or testicles (singular: testis), which are the site of sperm development and maturation. Testes develop from the same tissue that produces ovaries in females; however, in terrestrial mammals, the cells that produce the testes migrate from within the body cavity to become external to the body during development. Why are testes external to the body in terrestrial mammals? Sperm become immobile when kept at body temperature; therefore, the scrotum and penis are external to the body in land mammals and kept at about 2 °  C lower than body temperature to maintain sperm motility. In cases where the testes do not descend through the abdominal cavity during fetal development, infertility can occur in land mammals due to the higher body temperature. Though sperm must be produced and stored at temperatures lower than body temperature in the testes, sperm are warmed to body temperature when deposited in the female reproductive tract. The immediate warming of sperm causes them to experience a burst of swimming activity, but then they begin to lose motility after several hours at body temperature.

Within the testes, sperm are produced in structures called the  seminiferous tubules .  Sperm production is regulated by Sertoli cells which protect the sperm stem cells and promote their development, and cells of Leydig  which produce testosterone and regulate sperm development. Sperm mature as they proceed from the periphery to the lumen (interior) of the seminiferous tubules.

When the sperm have developed flagella and are nearly mature, they leave the testes and enter the epididymis , a structure which wraps around the testes and the location where sperm mature. During ejaculation, the sperm leave the epididymis and enter the vas deferens , which carries the sperm, behind the bladder, and forms the ejaculatory duct with the duct from the seminal vesicles.

Semen is a mixture of sperm and spermatic duct secretions and fluids from accessory glands. These glands are the seminal vesicles , the prostate gland , and the bulbourethral gland (all of which are illustrated above); together these glands contribute most of the semen’s volume:

• The seminal vesicles are a pair of glands that make thick, yellowish, and alkaline solution. As sperm are only motile in an alkaline environment, a basic pH is important to reverse the acidity of the vaginal environment. The solution also contains mucus, fructose (a source of energy for the sperm cells), a coagulating enzyme, ascorbic acid (vitamin C), and local-acting hormones called prostaglandins (may help stimulate smooth muscle contractions in the uterus). The seminal vesicle glands account for 60 percent of the bulk of semen.
• The  prostate gland acts as both a muscle and a gland. The muscle provides much of the force for ejaculation to occur. The glandular tissue makes a thin, milky fluid that contains citrate (stimulates sperm motility), enzymes, and prostate specific antigen (PSA). PSA is a proteolytic enzyme that helps to liquefy the ejaculate several minutes after release from the male. Prostate gland secretions account for about 30 percent of the bulk of semen.
• The bulbourethral gland   releases its secretion just before release of the bulk of the semen. The mucous secretions of this gland help lubricate and neutralize any acid residue in the urethra left over from urine. Secretions from the bulbourethral gland can also contain a few sperm; since these secretions are released prior to ejaculation, withdrawal of the penis from the vagina before ejaculation to prevent pregnancy may not work if sperm are present in the bulbourethral gland secretions.

Male Gametogenesis: Spermatogenesis

Spermatogenesis , illustrated below, occurs in the seminiferous tubules in the testes. Sperm stem cells, called spermatogonia , are present at birth but are inactive until puberty, when hormones from the pituitary cause the activation of the spermatogonia and the continuous production of sperm. Sperm production continues into old age. To produce sperm, a cell called a spermatocyte (a precursor to sperm) undergoes meiosis to produce four haploid spermatids (immature sperm). Once the spermatid develops a flagellum, (a tail that allows it to swim), it is called a  sperm cell . Four sperm cells result from each spermatocyte that goes through meiosis. (Scroll up to compare this process to oogenesis in human females, and see how many similarities and differences you can identify.)

Hormonal Control of Spermatogenesis

The information below was adapted from OpenStax Biology 43.4

Now that we have discussed the structures and processes of spermatogenesis, we’ll move into discussion of hormone regulation. Just like oogenesis, spermatogenesis is controlled by follicle-stimulated hormone (FSH) and luteinizing hormone (LH). Testosterone also plays a role in spermatogenesis:

• FSH stimulates activity of the Sertoli cells to nourish the developing sperm and promote their development. Sertoli cells are located within the seminiferous tubules, and play an analogous role to follicle cells in the ovaries.
• LH stimulates the Leydig cells to produce testosterone, which promotes spermatogenesis. Leydig cells are located in the testes, outside of the seminiferous tubules.
• Testosterone  further stimulates spermatogenesis by promoting maturation of the sperm after completing meiosis.

While this doesn’t occur in a monthly cycle as in females, the hormones do interact in a negative feedback cycle when sperm counts get too high (over about 20 million/ml): rising testosterone levels cause Sertoli cells to release the hormone inhibin, which acts on the hypothalamus and pituitary gland to inhibit the release of FSH and LH.  The inhibition causes spermatogenesis to slow down; once the sperm levels are reduced, the Sertoli cells stop releasing inhibin, and the sperm count increases.

This video provides a great overview of the anatomy and function of the human male reproductive system:

Oogenesis vs Spermatogenesis

As we’ve seen in this reading and the videos, both eggs and sperm are produced via meiosis, but there are some big differences:

• Initiation : Egg production begins during embryonic development (before birth), then is arrested during meiosis until puberty; sperm production does not begin until puberty
• Completion : Egg production is not actually completed until after fertilization (!), while sperm production is complete prior to ejaculation
• Number : Egg production results in only a single egg from each egg stem cell; sperm production results in four sperm from each sperm stem cell.
• Timing : Once an individual enters puberty, sperm production is continuous in a “conveyor belt” process; egg production occurs one-at-a-time at each menstrual cycle.

Contraception and Birth Control

The information below was adapted from  OpenStax Biology 43.5

We’ll wrap this discussion up with an overview of contraception. Contraception (prevention of pregnancy), can be categorized by according to whether they block gamete production or gamete union (fertilization):

• Hormone-based birth control methods use synthetic progesterone (sometimes in combination with estrogen), which inhibits production of FSH and LH, and thus prevent an egg from being maturing or being released. Progesterone is the primary hormone that blocks FSH and LH release, but estrogen enhances its effect and increases the reliability of this method. This method includes “the pill” as well as other methods of delivering the hormone(s) such as implants under the skin; methods such as skin implants are more reliable due to the continuous release of progesterone.
• Intrauterine devices (IUDs) are small T-shaped devices that are inserted into the uterus. IUDs induce an inflammatory response in the uterus that creates a toxic environment to the sperm and prevents them from reaching the oviducts. Some IUDs that contain progesterone which is continually secreted to suppress egg production and ovulation; others are copper-coated which alters the cervical mucus making it more difficult for sperm to reach the egg. Both types of IUDs are more reliable than standard hormone-based birth control.
• Emergency contraception, also known as “Plan B” or the “morning-after pill” is a hormone-based method of contraception containing a high dose of synthetic progesterone, which temporarily blocks egg maturation and ovulation, allowing time for sperm to die in the oviduct before the egg is released. It can also act after ovulation slowing down movement of the egg and thickening cervical mucus which slows movement of sperm. One common misconception about emergency contraception is that it prevents implantation after fertilization; however, it has no impact after fertilization.
• Barrier methods, such as condoms, cervical caps, and diaphragms, block sperm from entering the uterus, preventing fertilization. Spermicides are chemicals that are placed in the vagina that kill sperm. Sponges, which are saturated with spermicides, are placed in the vagina at the cervical opening. Combining spermicides with barrier methods is more effective than using either alone.
• Vasectomies block sperm from exiting the body during ejaculation (contrary to popular misconception, vasectomies do not block sperm production – only sperm release). A section of the vas deferens is removed, so sperm are still produced but cannot reach the urethra to be ejaculated. No other structures are affected, and so all other components of ejaculate are still present. Vasectomy is one of the most effective methods of birth control.
• Tubal ligation is the female equivalent to a vasectomy in that it involves severing and sealing the oviducts; eggs are still produced and ovulated from the ovaries, but they are unable to reach the oviducts for fertilization. However, unlike vasectomies which are performed through the scrotum, tubal ligation requires abdominal surgery to reach the oviducts. Tubal ligation is also among the most effective methods of birth control.

Methods of contraception to prevent pregnancy have varying probabilities of success. In the diagram below, the failure rate is the given as the percent of women who become pregnant during the first year of use of that method. Work through the methods in this diagram to determine the most effective strategies for preventing pregnancy. Methods in combination, such as spermicidal chemicals and barrier, prevent pregnancy more effectively than do the methods when used separately.

This video provides a quick overview of hormone-based birth control, with emphasis on emergency contraception:

• Entries RSS
• Comments RSS
• Sites@GeorgiaTech

Creative Commons License

Vannevar bush.

“Science has a simple faith, which transcends utility. It is the faith that it is the privilege of man to learn to understand, and that this is his mission.”

18.1 How Animals Reproduce

Learning objectives.

• Describe advantages and disadvantages of asexual and sexual reproduction
• Discuss asexual reproduction methods
• Discuss sexual reproduction methods
• Discuss internal and external methods of fertilization

Some animals produce offspring through asexual reproduction while other animals produce offspring through sexual reproduction. Both methods have advantages and disadvantages. Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly; these are two advantages that asexually reproducing organisms have over sexually reproducing organisms. In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment. In an unstable or unpredictable environment, species that reproduce asexually may be at a disadvantage because all the offspring are genetically identical and may not be adapted to different conditions.

During sexual reproduction , the genetic material of two individuals is combined to produce genetically diverse offspring that differ from their parents. The genetic diversity of sexually produced offspring is thought to give sexually reproducing individuals greater fitness because more of their offspring may survive and reproduce in an unpredictable or changing environment. Species that reproduce sexually (and have separate sexes) must maintain two different types of individuals, males and females. Only half the population (females) can produce the offspring, so fewer offspring will be produced when compared to asexual reproduction. This is a disadvantage of sexual reproduction compared to asexual reproduction.

Asexual Reproduction

Asexual reproduction occurs in prokaryotic microorganisms (bacteria and archaea) and in many eukaryotic, single-celled and multi-celled organisms. There are several ways that animals reproduce asexually, the details of which vary among individual species.

Fission , also called binary fission, occurs in some invertebrate, multi-celled organisms. It is in some ways analogous to the process of binary fission of single-celled prokaryotic organisms. The term fission is applied to instances in which an organism appears to split itself into two parts and, if necessary, regenerate the missing parts of each new organism. For example, species of turbellarian flatworms commonly called the planarians, such as Dugesia dorotocephala , are able to separate their bodies into head and tail regions and then regenerate the missing half in each of the two new organisms. Sea anemones (Cnidaria), such as species of the genus Anthopleura ( Figure 18.2 ), will divide along the oral-aboral axis, and sea cucumbers (Echinodermata) of the genus Holothuria, will divide into two halves across the oral-aboral axis and regenerate the other half in each of the resulting individuals.

Budding is a form of asexual reproduction that results from the outgrowth of a part of the body leading to a separation of the “bud” from the original organism and the formation of two individuals, one smaller than the other. Budding occurs commonly in some invertebrate animals such as hydras and corals. In hydras, a bud forms that develops into an adult and breaks away from the main body ( Figure 18.3 ).

Link to Learning

View this video to see a hydra budding.

Fragmentation

Fragmentation is the breaking of an individual into parts followed by regeneration. If the animal is capable of fragmentation, and the parts are big enough, a separate individual will regrow from each part. Fragmentation may occur through accidental damage, damage from predators, or as a natural form of reproduction. Reproduction through fragmentation is observed in sponges, some cnidarians, turbellarians, echinoderms, and annelids. In some sea stars, a new individual can be regenerated from a broken arm and a piece of the central disc. This sea star ( Figure 18.4 ) is in the process of growing a complete sea star from an arm that has been cut off. Fisheries workers have been known to try to kill the sea stars eating their clam or oyster beds by cutting them in half and throwing them back into the ocean. Unfortunately for the workers, the two parts can each regenerate a new half, resulting in twice as many sea stars to prey upon the oysters and clams.

Parthenogenesis

Parthenogenesis is a form of asexual reproduction in which an egg develops into an individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process in the species. Parthenogenesis occurs in invertebrates such as water fleas, rotifers, aphids, stick insects, and ants, wasps, and bees. Ants, bees, and wasps use parthenogenesis to produce haploid males (drones). The diploid females (workers and queens) are the result of a fertilized egg.

Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Parthenogenesis has been observed in species in which the sexes were separated in terrestrial or marine zoos. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males. It is possible that the asexual reproduction observed occurred in response to unusual circumstances and would normally not occur.

Sexual Reproduction

Sexual reproduction is the combination of reproductive cells from two individuals to form genetically unique offspring. The nature of the individuals that produce the two kinds of gametes can vary, having for example separate sexes or multiple sexes in each individual. Sex determination, the mechanism that determines which sex an individual develops into, also can vary.

Hermaphroditism

Hermaphroditism occurs in animals in which one individual has both male and female reproductive systems. Invertebrates such as earthworms, slugs, tapeworms, and snails ( Figure 18.5 ) are often hermaphroditic. Hermaphrodites may self-fertilize, but typically they will mate with another of their species, fertilizing each other and both producing offspring. Many species have specific mechanisms in place to prevent self-fertilization, because it is an extreme form of inbreeding and usually produces less fit offspring. Hermaphrodite is not an accepted term for humans, and does not describe differences in their sexual development. Intersex people are those whose sex traits or reproductive anatomy develops differently from the typical ways humans develop, and can include hormonal, chromosomal, or anatomical differences.

Sex Determination

Pioneering scientist Nettie Stevens was the first to observe chromosomal differences between the different sexes of organisms. Using a microscope to observe mealworm cells, she noted that one chromosome was notably different between females and males, and she concluded that those chromosomes were the most likely determinants of the worms' sex. She later studied other insects, and her discoveries were confirmed by other scientists. (Stevens was initially denied credit due to her gender, but later publications acknowledged her critical role.) Mammalian sex is determined genetically by the combination of X and Y chromosomes. Individuals homozygous for X (XX) are female and heterozygous individuals (XY) are male. In mammals, the presence of a Y chromosome causes the development of male characteristics and its absence results in female characteristics. The XY system is also found in some insects and plants.

Bird sex determination is dependent on the combination of Z and W chromosomes. Homozygous for Z (ZZ) results in a male and heterozygous (ZW) results in a female. Notice that this system is the opposite of the mammalian system because in birds the female is the sex with the different sex chromosomes. The W appears to be essential in determining the sex of the individual, similar to the Y chromosome in mammals. Some fish, crustaceans, insects (such as butterflies and moths), and reptiles use the ZW system.

More complicated chromosomal sex determining systems also exist. For example, some swordtail fish have three sex chromosomes in a population.

The sex of some other species is not determined by chromosomes, but by some aspect of the environment. Sex determination in alligators, some turtles, and tuataras, for example, is dependent on the temperature during the middle third of egg development. This is referred to as environmental sex determination, or more specifically, as temperature-dependent sex determination. In many turtles, cooler temperatures during egg incubation produce males and warm temperatures produce females, while in many other species of turtles, the reverse is true. In some crocodiles and some turtles, moderate temperatures produce males and both warm and cool temperatures produce females.

Individuals of some species change their entire set of reproductive organs during their lives, switching from one to the other. If the individual is born with an ovarian system of organs first, it is termed protogyny or “first female,” if it is born with a testicular system of organs first, it is termed protandry or “first male.” Oysters are born with male morphology, grow in size, and change body parts and lay eggs. The wrasses, a family of reef fishes, are all sequential hermaphrodites. Some of these species live in closely coordinated schools with a dominant male and a large number of smaller females. If the male dies, a female increases in size, changes sex, and becomes the new dominant male.

Fertilization

The fusion of a sperm and an egg is a process called fertilization. This can occur either inside ( internal fertilization ) or outside ( external fertilization ) the body of the female. Humans provide an example of the former, whereas frog reproduction is an example of the latter.

External Fertilization

External fertilization usually occurs in aquatic environments where both eggs and sperm are released into the water. After the sperm reaches the egg, fertilization takes place. Most external fertilization happens during the process of spawning where one or several females release their eggs and the male(s) release sperm in the same area, at the same time. The spawning may be triggered by environmental signals, such as water temperature or the length of daylight. Nearly all fish spawn, as do crustaceans (such as crabs and shrimp), mollusks (such as oysters), squid, and echinoderms (such as sea urchins and sea cucumbers). Frogs, corals, squid, and octopuses also spawn ( Figure 18.6 ).

Internal Fertilization

Internal fertilization occurs most often in terrestrial animals, although some aquatic animals also use this method. Internal fertilization may occur by the male directly depositing sperm in the female during mating. It may also occur by the male depositing sperm in the environment, usually in a protective structure, which a female picks up to deposit the sperm in the reproductive tract. There are three ways that offspring are produced following internal fertilization. In oviparity , fertilized eggs are laid outside the parent’s body and develop there, receiving nourishment from the yolk that is a part of the egg ( Figure 18.7 a ). This occurs in some bony fish, some reptiles, a few cartilaginous fish, some amphibians, a few mammals, and all birds. Most non-avian reptiles and insects produce leathery eggs, while birds and some turtles produce eggs with high concentrations of calcium carbonate in the shell, making them hard. Chicken eggs are an example of a hard shell. The eggs of the egg-laying mammals such as the platypus and echidna are leathery.

In ovoviparity , fertilized eggs are retained in the female, and the embryo obtains its nourishment from the egg’s yolk. The eggs are retained in the female’s body until they hatch inside the body, or the female lays the eggs right before they hatch. This process helps protect the eggs until hatching. This occurs in some bony fish (like the platyfish Xiphophorus maculatus, Figure 18.7 b ), some sharks, lizards, some snakes (garter snake Thamnophis sirtalis ), some vipers, and some invertebrate animals (Madagascar hissing cockroach Gromphadorhina portentosa ).

In viviparity the young are born alive. They obtain their nourishment from the female and are born in varying states of maturity. This occurs in most mammals ( Figure 18.7 c ), some cartilaginous fish, and a few reptiles.

As an Amazon Associate we earn from qualifying purchases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/concepts-biology/pages/1-introduction

• Authors: Samantha Fowler, Rebecca Roush, James Wise
• Publisher/website: OpenStax
• Book title: Concepts of Biology
• Publication date: Apr 25, 2013
• Location: Houston, Texas
• Book URL: https://openstax.org/books/concepts-biology/pages/1-introduction
• Section URL: https://openstax.org/books/concepts-biology/pages/18-1-how-animals-reproduce

© Apr 26, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

Chapter 13: Introduction to Animal Reproduction and Development

In the animal kingdom, each species has its unique adaptations for reproduction. Asexual reproduction produces genetically identical offspring (clones), whereas in sexual reproduction, the genetic material of two individuals combines to produce offspring that are genetically different from their parents. During sexual reproduction the male gamete (sperm) may be placed inside the female’s body for internal fertilization, the sperm may be left in the environment for the female to pick up and place in her body, or both sperm and eggs may be released into the environment for external fertilization. Seahorses provide an example of the latter, but with a twist (Figure 13.1). Following a mating dance, the female releases eggs into the male seahorse’s abdominal brood pouch and the male releases sperm into the water, which then find their way into the brood pouch to fertilize the eggs. The fertilized eggs develop in the pouch for several weeks.

Concepts of Biology - 1st Canadian Edition Copyright © 2015 by Charles Molnar and Jane Gair is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

Share This Book

• Biology Article
• Reproduction In Animals

How Animals Reproduce

What is reproduction.

Reproduction is the process of producing individuals of the same kind. Most organisms reproduce by mating, which increases the genetic variability of the organism. The males and females have separate reproductive organs known as gonads. These gonads produce gametes that fuse together to form a single cell called the zygote.

Few animals such as earthworms, snails, slugs, etc. are hermaphrodites and possess male and female reproductive organs in the same organism.

Also Read:   Reproduction

Table of Contents

Binary Fission

Fragmentation, regeneration, parthenogenesis, modes of reproduction.

Depending on the number of parents involved, there are different modes of reproduction. In animals is two types of reproduction:

• Sexual Reproduction.
• Asexual Reproduction.

Also Read: Modes of Reproduction

Let us go through the following reproduction notes to explore sexual and asexual reproduction in animals.

Sexual Reproduction in Animals

The process in which the male and female gametes fuse together to form a new individual is called sexual reproduction. Let us have a brief account of the human reproductive organs and their role in reproduction.

Also Read:   Sexual Reproduction

Reproductive Organs

The male reproductive organs comprise a pair of testes, sperm ducts, and a penis. The sperms are produced by the testes. The sperms are very small in size with a head, a middle piece, and a tail.

The female reproductive organs comprise a pair of ovaries, oviducts, and the uterus. The eggs (ova) are produced by the ovaries. The development of the baby takes place in the uterus. A mature egg is released into the oviduct every month.

Process of Sexual Reproduction in Animals

Fertilization

The semen contains millions of sperm. A single sperm fuses with the ova during fertilization. The nuclei of the egg and the sperm fuse together to form a single nucleus. Thus, a zygote is formed.

Fertilization is of two types:

• Internal Fertilization

The fertilization that takes place inside the body of the female is known as internal fertilization. For eg., humans, cows, dogs, etc. This method is more prevalent in terrestrial animals. However, some aquatic animals also adopt this method. This may take place by direct introduction of sperms by the male in the female reproductive tract, or the male deposits the sperms in the environment which is picked up by the female in her reproductive tract.

There are three ways by which offspring are produced by internal fertilization:

Oviparity – The fertilized eggs are laid outside, where they receive nourishment from the yolk.

Ovoviviparity – The fertilized eggs are retained in the female’s body where they receive nourishment from the yolk. The eggs are laid right before they are hatched.

Viviparity – The offspring are born directly instead of hatching from the eggs. They receive nutrition from the mother. This can be seen in mammals.

• External Fertilization

The fertilization that takes place outside the female is called external fertilization. For eg., frogs, and fish. Most fertilization takes place during the process of spawning. Environmental signals such as water temperature trigger spawning.

Embryo Development

The zygote divides repeatedly to form a ball of cells. This is known as the developing embryo. These cells differentiate into respective tissues and organs. The embryo gets implanted in the uterine wall. This process is known as implantation .

When all the body parts of the embryo start being visible, it is called a foetus. The child is developed after nine months in humans.

Viviparous and Oviparous Animals

Oviparous and viviparous animals are two different groups of animals, which are classified on the basis of fertilization. The main difference between oviparous and viviparous animals are listed below:

Asexual Reproduction in Animals

Besides sexual reproduction, the other major type of reproduction seen in the animal kingdom is asexual reproduction. This type of reproduction is mostly observed in lower organisms and unicellular microbes.

It is the process in which a new individual is formed by the involvement of a single parent without the involvement of the gamete formation. The individuals produced are genetically and morphologically similar. The cells divide by mitotic division and no fertilization takes place. The division occurs very rapidly.

Types Of Asexual Reproduction

Asexual Reproduction is of the following types:

It is seen in amoeba and euglena. The parent cell undergoes mitosis and increases in size. The nucleus also divides. Two identical daughter cells are obtained, each containing a nucleus. Prokaryotes like bacteria majorly reproduce by binary fission.

In this, the offspring grows out of the body of the parent. It remains attached to the parent until it matures. After maturation, it detaches itself from the parent and lives as an individual organism. This form of reproduction is most common in Hydras.

In some organisms like Planarians, when the body of an organism breaks into several pieces each piece grows into an individual offspring. This is known as fragmentation. It can occur through accidental damage by predators or otherwise, or as a natural form of reproduction. In a few animals such as sea stars, a broken arm grows into a complete organism.

It is a modified form of fragmentation and occurs mostly in Echinoderms. When a part of an organism, like an arm, detaches from the parent body, it grows into a completely new individual. This is known as regeneration.

This is a form of asexual reproduction where the egg develops without fertilization. This process occurs in bees, wasps, ants, aphids, rotifers, etc. Ants, wasps, and bees produce haploid males. Parthenogenesis has been observed in a few vertebrates such as hammerhead sharks, Komodo dragons, and blacktop sharks when the females were isolated from the males.

Frequently Asked Questions – FAQs

What are the advantages of sexual reproduction over asexual reproduction.

a) Variations: Due to recombination and crossing over, sexual reproduction brings about variations in species. Variations are essential for the individuality and evolution of species. b) Better adaptability: Increased variability due to sexual reproduction helps in better adaptability of species. c) Evolution: It helps in the evolution of species. Harmful traits can be removed by the selection of better-adapted individuals or maybe not be expressed due to the reshuffling of gene pairs.

What is the difference between sexual reproduction and asexual reproduction?

Asexual: ——— 1.) Single parent 2.) Offspring are genetically identical to each other and to their parent 3.) No Internal fertilization or External fertilization 4.) No gametes 5.) No mixing of hereditary material

Recommended Video:

For more details on Reproduction in Animals,  different modes of reproduction, or any other related topics, keep visiting BYJU’S website or download BYJU’S app for further reference.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

Visit BYJU’S for all Biology related queries and study materials

Your result is as below

Request OTP on Voice Call

Leave a Comment Cancel reply

Your Mobile number and Email id will not be published. Required fields are marked *

Post My Comment

It’s Very useful

very very very very very very very useful

Excellent work.

Thanks a lot, very useful

Register with BYJU'S & Download Free PDFs

Register with byju's & watch live videos.

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Middle school biology - NGSS

Course: middle school biology - ngss   >   unit 2, sexual and asexual reproduction.

• Understand: sexual and asexual reproduction

Key points:

• Reproduction is the process of making new organisms. Parent organisms reproduce to make offspring .
• When organisms reproduce, they pass their genetic information to their offspring. This genetic information includes genes , which are pieces of hereditary material that affect an organism's inherited traits.
• During asexual reproduction , a single parent produces offspring. The offspring have the same genes, and therefore the same inherited traits, as the parent.
• During sexual reproduction , two parents produce offspring. The offspring have a mix of genes from both parents. As a result, offspring have a different set of traits compared to either parent.

Want to join the conversation?

• Upvote Button navigates to signup page
• Downvote Button navigates to signup page
• Flag Button navigates to signup page

Plant and Animal Reproduction

While all organisms reproduce, not all organisms reproduce the same way. Explore the similar and different ways that plants and animals pass on their genes.

Biology, Genetics

Loading ...

All organisms reproduce, which is the biological process where an organism produces and/or gives birth to another organism. Both plants and animals reproduce, though they have evolved the processes so that they overlap and diverge from each other in several ways. Types of Reproduction There are two types of reproduction: asexual reproduction and sexual reproduction . A sexual reproduction involves a single parent that produces a genetically identical offspring. Sexual reproduction involves two parents of the opposite sex. A male plant or animal contributes genetic material in the form of sperm or pollen to a female plant or animal's egg. The offspring then has genetic material from both parents. Different plants and animals can reproduce either asexually or sexually; however, a sexual reproduction is more common among plants than animals. Asexual and sexual reproduction each have benefits and drawbacks. Organisms that reproduce asexually have the advantage of producing several genetically identical offspring quickly and with little energy. On the other hand, the lack of genetic diversity among asexual offspring means they have a lower chance of adapting to an unstable environment. By contrast, organisms that reproduce sexually have the advantage of producing a genetically diverse offspring, which is able to adapt to its environment. But sexual reproduction comes at a cost, requiring more time and energy to produce an offspring than a sexual reproduction . Asexual Reproduction There are a variety of ways plants can reproduce asexually, or without a partner. For example, some nonflowering plants, such as moss and algae, reproduce by spore formation. Spores grow on a plant, then break off and grow into separate organisms. Other plants, such as strawberries, are able to reproduce asexually through vegetative propagation . This process involves using a part of a plant, such as a root or stem, to produce a new plant, and can happen either naturally or artificially. Other artificial methods, such as grafting , involve combining two plants into one by attaching the top part of a plant, called a scion , to the lower part of a plant, called a rootstock . Sexual Reproduction and Fertilization Many plants and most animals require partners to reproduce. Plants and animals share their genetic material in a process called fertilization . In plants, fertilization happens when the male shares pollen , which contains its genetic material, with a female plant's egg. In flowering plants, an egg is fertilized by cross- pollination . This process often requires an insect, such as a bee, that transfers grains of pollen from the male part of a flower, which is called the anther , to the female part of a flower, which is called the stigma . Once the pollen lands on the stigma , it passes through a long, tube-like structure called a style to reach the plant's ovaries. This part of the reproductive organ is where fertilization takes place. Some plants, called hermaphrodites , have male and female parts on the same plant, and are able to self-pollinate. Animals, by contrast, do not depend on third parties like insects for fertilization . As mobile creatures, animals can directly transfer sperm to an egg by physically interacting with each other. They often perform various mating rituals in order to attract a potential partner. Embryonic Development Once a plant or animal egg is fertilized, it starts developing into a multicellular organism. During this early stage, the fertilized egg is called an embryo. Despite differences in the fertilization process, the development of plant and animal embryos is similar. A plant embryo is contained within a seed, which provides the nutrients it needs to grow, while an animal embryo develops within an egg, outside the organism, or within a uterus, inside the female parent organism. Birth and Germination Plants and animals also differ with respect to how they give birth. Animals exit the female's uterus as a newborn or hatch from an egg that has already left the female's body. A plant, by contrast, begins its life by sprouting from a seed. The plant releases the seed, which begins to grow once it is in the soil and the conditions are right. After the seed has sprouted into a plant, it can collect additional nutrients through its roots.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

October 19, 2023

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Animal Reproduction (ISSN 1984-3143, online and 1806-9614, print) is an open access peer-reviewed journal published by the Colégio Brasileiro de Reprodução Animal - CBRA (Brazilian College of Animal Reproduction). The journal is published quarterly featuring English articles with research on the basic, applied and biotechnological aspects of animal reproductive biology. The abbreviated name to be used in citations that require that style is Anim. Reprod.

Mission and scope

Animal Reproduction (AR) publishes original scientific papers and invited literature reviews, in the form of Basic Research, Biotechnology, Applied Research and Review Articles, with the goal of contributing to a better understanding of phenomena related to animal reproduction.

The scope of the journal applies to students, researchers and practitioners in the fields of veterinary, biology and animal science, also being of interest to practitioners of human medicine. Animal Reproduction Journal is the official organ of the Brazilian College of Animal Reproduction in Brasil.

Open Access

Indexing sources, preserved and archived in.

Animal Reproduction 50th anniversary

Editor-in-chief.

Carlos Eduardo Ambrósio Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo - FZEA/Universidade de São Paulo, SP, Pirassununga, SP, Brasil

Felipe Perecin Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo - FZEA/Universidade de São Paulo, Pirassununga, SP, Brasil

Ivan Cunha Bustamante Filho Universidade do Vale do Taquari - UNIVATES, Lajeado, RS, Brasil

Associated editors

Angela Maria Gonella Diaza University of Florida, Marianna, FL, USA

Joanna Maria Gonçalves de Souza Fabjan Faculdade de Veterinária, Universidade Federal Fluminense - UFF, Niterói, RJ, Brasil

Zamira Gibb The University of Newcastle, Callaghan, NSW, Australia

Editorial Board

Andrzej Bartke Southern Illinois University, Springfield, Il, USA

Antônio Carlos S. Castro Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil

Arlindo A.A. Moura Universidade Federal Ceará, Fortaleza, CE, Brasil

Barry D. Bavister University of New Orleans, New Orleans, LO, USA

Bart Gadella Ghent University, Belgium and Utrecht University, The Netherlands

Brian Setchell University of Adelaide, Hanson Institute, Adelaide, Australia

Daniele dos Santos Martins Universidade de São Paulo, Pirassununga, SP, Brazil

Edward L. Squires Colorado State University, USA

Fernanda da Cruz Landim-Alvarenga Universidade Estadual de São Paulo, Botucatu SP, Brasil

Goro Yoshizaki Tokyo University of Marine Science and Technology, Tokyo, Japan

Heriberto Rodriguez-Martinez BHK/O&G Linköping University, SE, Linköping, Sweden

Hugo P. Godinho – Pontifica Universidade Católica/Minas and Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil

João Carlos Deschamps Universidade Federal de Pelotas, Pelotas, RS, Brasil

J.A. (Lulu) Skidmore The Camel Reproduction Centre, Dubai, UAE

Katrin Hinrichs Texas A&M University, College Station, TX, USA

Keith Betteridge University of Guelph, Toronto, Canada

Luis Renato França Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil

Mário Binelli University of Florida, Gainsvillte, FL, USA

Rex A. Hess University of Illinois, Urbana-Champaign,Urbana, USA

Rüdiger W. Schulz Utrecht University, Utrecht, The Netherlands

Sue M. McDonnell University of Pennsylvania, Philadelphia, PA, USA

Tiziana A.L. Brevini Università degli Studi di Milano, Milan, Italy

Wilma de Grava Kempinas Universidade Estadual de São Paulo, Botucatu SP,Brasil, Brasil

Editor-in-chief Carlos Eduardo Ambrósio Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo - FZEA/Universidade de São Paulo, SP, Pirassununga, SP, Brasil Felipe Perecin Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo - FZEA/Universidade de São Paulo, Pirassununga, SP, Brasil Ivan Cunha Bustamante Filho Universidade do Vale do Taquari - UNIVATES, Lajeado, RS, Brasil

Periodicity: Quarterly

Published by: Colégio Brasileiro de Reprodução Animal

Google Scholar

2022 h5 index :  21 more details

Anim Reprod

We will keep fighting for all libraries - stand with us!

Internet Archive Audio

• This Just In
• Grateful Dead
• Old Time Radio
• 78 RPMs and Cylinder Recordings
• Audio Books & Poetry
• Computers, Technology and Science
• Music, Arts & Culture
• News & Public Affairs
• Spirituality & Religion
• Radio News Archive

• Flickr Commons
• Occupy Wall Street Flickr
• NASA Images
• Solar System Collection
• Ames Research Center

• All Software
• Old School Emulation
• MS-DOS Games
• Historical Software
• Classic PC Games
• Software Library
• Kodi Archive and Support File
• Vintage Software
• CD-ROM Software
• CD-ROM Software Library
• Software Sites
• Tucows Software Library
• Shareware CD-ROMs
• Software Capsules Compilation
• CD-ROM Images
• ZX Spectrum
• DOOM Level CD

• Smithsonian Libraries
• FEDLINK (US)
• Lincoln Collection
• American Libraries
• Canadian Libraries
• Universal Library
• Project Gutenberg
• Children's Library
• Biodiversity Heritage Library
• Books by Language
• Additional Collections

• Prelinger Archives
• Democracy Now!
• Occupy Wall Street
• TV NSA Clip Library
• Animation & Cartoons
• Arts & Music
• Computers & Technology
• Cultural & Academic Films
• Ephemeral Films
• Sports Videos
• Videogame Videos
• Youth Media

Search the history of over 866 billion web pages on the Internet.

Mobile Apps

• Wayback Machine (iOS)
• Wayback Machine (Android)

Browser Extensions

Archive-it subscription.

• Explore the Collections
• Build Collections

Save Page Now

Capture a web page as it appears now for use as a trusted citation in the future.

Please enter a valid web address

• Donate Donate icon An illustration of a heart shape

An essay on animal reproductions

Bookreader item preview, share or embed this item, flag this item for.

• Graphic Violence
• Explicit Sexual Content
• Hate Speech
• Misinformation/Disinformation
• Marketing/Phishing/Advertising
• Misleading/Inaccurate/Missing Metadata

Title and copyright on the cover page.

plus-circle Add Review comment Reviews

Download options.

For users with print-disabilities

IN COLLECTIONS

Uploaded by Unknown on August 21, 2018

SIMILAR ITEMS (based on metadata)

The Animal Domestication Experiment as a Model of the Evolutionary Process: A New Insight into Evolution Under Selection Targeting Regulatory Systems

• First Online: 30 March 2017

Cite this chapter

• Ludmila N. Trut 5 ,
• Yury E. Herbek 5 ,
• Oleg V. Trapezov 5 ,
• Sergey A. Lashin 5 ,
• Yury G. Matushkin 5 ,
• Arcady L. Markel 5 &
• Nikolay A. Kolchanov 5  

The paper considers the main results of the long-lasting experimental domestication of animals—foxes, minks and brown rats. The following important conclusions have been made. Fundamental to the domestication process is the intensive selection of animals for human-tolerant behavior and the capability to adapt to the emerging social structure “human—domestication object”. Intensive selection for behavior and, therefore, for the central regulatory systems, which control the functioning of the entire organism, leads to large amounts of variability in the population under domestication. Stress caused by rapid environmental changes, with its neurohormonal mechanisms of regulation of genetic processes, has an important role in the induction of variability. These considerations prompted Dmitry Belyaev, mutational variability is rendered neutral. Under directional (and destabilizing) selection, hidden mutational variability becomes exposed. If the regulatory circuits with negative feedback are lost, hidden genotypic variability becomes exposed and individuals with major phenotypic aberrations occur.

How do biological systems evolve in time? A century ago there lived Crocodile No. 17, now there lives Crocodile No. 187, who is quite a different crocodile, so what have we got? We’ve got some “crocodilery”, but what is that? …. a type of original control systems… this is fundamental to the modern concept that is absolutely required for a correct, efficient and fast - paced development of biology in the near future . N.W. Timofeeff-Ressovsky (“ Genetics, evolution, significance of methodology in natural sciences ”).

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

• Available as PDF
• Read on any device
• Instant download
• Own it forever
• Available as EPUB and PDF
• Compact, lightweight edition
• Dispatched in 3 to 5 business days
• Free shipping worldwide - see info
• Durable hardcover edition

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Similar content being viewed by others

DNA Dispose, but Subjects Decide. Learning and the Extended Synthesis

The silver fox domestication experiment, bergmann’s rule, adaptation, and thermoregulation in arctic animals: conflicting perspectives from physiology, evolutionary biology, and physical anthropology after world war ii.

Afonnikov DA, Kolchanov NA (2001) Konservativnye osobennosti DNK-svyazyvayushchikh domenov klassa “gomeodomen”, obuslovlennye koadaptivnymi zamenami aminokislotnykh ostatkov (The conserved characteristics of DNA-binding domains belonging to the homeodomain class that are associated with coadaptive substitutions of amino acid residues). Proc USSR Acad Sci 380:691–695 (in Russian)

CAS   Google Scholar  

Afonnikov DA, Oshchepkov DYu, Kolchanov NA (2001) Detection of conserved physico-chemical characteristics of proteins by analyzing clusters of positions with co-ordinated substitutions. Bioinformatics 17:1035–1046

Article   CAS   PubMed   Google Scholar  

Aleshin VV, Petrov NB (2003) Uslovno neytralnye priznaki (Conditionally neutral characters). Priroda 12:25–34 (in Russian)

Google Scholar  

Belyaev DK (1972) Geneticheskie aspekty domestikatsii zhivotnykh (Genetic aspects of animal domestication). In: Matveev BS (ed) Problemy domestikatsii zhivotnykh i rasteniy (literally: Aspects of animal and plant domestication). Moscow, Nauka, pp 39–45 (in Russian)

Belyaev DK (1979) Nekotorye genetiko-evolyutsionnye problemy stressa i stressoustoychivosti [Some genetic and evolutionary aspects of stress and stress resistance]. Vestnik Akademii meditsinskikh nauk SSSR 7:9–14 (in Russian)

Belyaev DK (1982) Glavnoe bogatstvo chelovechestva (Humankind’s main treasure). Nauka i religiya 1:2–6 (in Russian)

Belyaev DK, Borodin PM (1982) The influence of stress on variation and its role in evolution. Biol Zentralblatt 100:705–714

Belyaev DK, Borodin PM (1985) Vliyanie stressa na nasledstvennost i ego rol v evolyutsii (Effects of stress on inheritance and its role in evolution). In: Evolyutsionnaya genetika (literally: Evolutionary genetics). Leningrad. Leningrad University, pp 35–39 (in Russian)

Belyaev DK, Ruvinsky AO, Borodin PM (1981) Inheritance of alternative states of the fused gene in mice. J Hered 72:107–112

Belyaev DK, Plyusnina IZ, Trut LN (1985) Domestication in the silver fox (Vulpes fulvus Desm): Changes in physiological boundaries of the sensitive period of primary socialization. Appl Anim Behav Sci 13:359–370

Berg RL (1993) Korrelyatsionnye pleyady i stabiliziruyushchiy otbor (Correlation pleiades and stabilizing selection). In: Genetika i evolyutsiya. Izbrannye trudy (literally: Genetics and evolution. Selected papers). Nauka, Novosibirsk, pp 137–178 (in Russian)

Boice R (1972) Some behavioral tests of domestication in Norway rats. Behaviour 42:198–231

Article   Google Scholar  

Calow P (1983) Evolutionary principles. Blackie & Son Ltd., Glasgow, p 105

Coppinger R, Feinstein M (1991) “Hark! Hark! The dogs do bark” and bark and bark. Smithsonian 119–129

Darwin Ch (1883) The variation of animals and plants under domestication, 2d edn. D. Appleton & Co., New York, p 429

Darwin Ch (1927) Proiskhozhdenie cheloveka i polovoy podbor (The descent of man, and selection in relation to sex). Polnoe sobranie sochineniy (literally: Complete works), vol 2, p 623 (in Russian)

Elena SF, Lenski RE (2003) Microbial genetics: evolution experiments with microorganisms: the dynamics and genetic bases of adaptation. Nat Rev Genet 4:457–469

Gogoleva SS, Volodina EV, Volodin IA, Kharlamova AV, Trut LN (2010) The gradual vocal responses to human-provoked discomfort in farmed silver foxes. Acta Ethol 13:75–85

Article   PubMed   PubMed Central   Google Scholar  

Gulevich RG, Plyusnina IZ, Prasolova LA, Oskina IN, Trut LN (2010) White spotting in Norway rats selected for tame behavior. J Zool 280:264–270

Gunbin KV, Suslov VV, Kolchanov NA (2007) Aromorphoses and the adaptive molecular evolution. VOGIS Herald 11:373–399

Hare B, Wobber V, Wrangham R (2012) The self-domestication hypothesis: evolution of bonobo psychology is due to selection against aggression. Anim Behav 83:573–585

Hedrich HJ (2000) Part 1. The history and development of the rat as a laboratory model. In: Krinke GJ (ed) The laboratory rat. AP, San Diego, pp 3–30

Chapter   Google Scholar  

Kolchanov NA (2003) Evolyutsiya regulyatornykh geneticheskikh system (The evolution of genetic regulatory systems). Theoretical workshop for geologists and biologists “The origin and evolution of living systems”. http://www.bionet.nsc.ru/live (in Russian)

Kolchanov NA, Shindyalov IN (1991) Teoreticheskoe issledovanie evolyutsii regulyatornykh konturov pri razlichnykh tipakh otbora (Theoretical study of the evolution of regulatory circuits under different types of selection). In: Smuny VK, Kolchanov NA, Ruvinsky AO (eds) Problemy genetiki i teorii evolyutsii (literally: Aspects of genetics and evolution theory). Nauka, Novosibirsk, pp 268–279 (in Russian)

Konoshenko MY (2012) Avtoreferat kandidatskoy dissertatsii (Author’s summary of his thesis for Candidate of Sciences). Novosibirsk, 2012. http://www.dissercat.com/content/povedencheskie-i-neirokhimicheskie-osobennosti-vnutrividovoi-agressii-u-serykh-krys-effekty

Krasilov VA (1986) Nereshennye problemy teorii evolyutsii (Yet unsolved problems in evolution theory). Far Eastern Scientific Center of the USSR Academy of Sciences, Vladivostok, 138 pp (in Russian)

Kukekova AV, Acland GM, Oskina IN, Kharlamova AV, Trut LN, Chase K, Lark KG, Erb HN, Aguirre GD (2006) The genetics of domesticated behavior in Canids: what can dogs and silver foxes tell us about each other? In: The Dog and Its Genome, pp 515–537

Kukekova AV, Trut LN, Chase K, Shepeleva DV, Vladimirova AV, Kharlamova AV, Oskina IN, Stepika A, Klebanov S, Erb HN, Acland GM (2008) Measurement of segregating behaviors in experimental silver fox pedigrees. Behav Genet 38:185–194

Article   PubMed   Google Scholar  

Kukekova AV, Trut LN, Chase K, Kharlamova AV, Johnson JL, Temnykh SV, Oskina IN, Gulevich RG, Vladimirova AV, Klebanov S et al (2011) Mapping loci for fox domestication: deconstruction/reconstruction of a behavioral phenotype. Behav Genet 41:593–606

Lashin SA, Matushkin YuG (2013) Multi-layer computer models of gene network evolution in diploid populations. FEBS J 280:563

Lashin SA, Klimenko AI, Mustafin ZS, Kolchanov NA, Matushkin YG (2014) HEC 2.0: improved simulation of the evolution of prokaryotic communities. Mat Bio Bioinf 9:585–596

Markel AL, Borodin PM (1980) The stress phenomenon: genetic and evolutionary approach. Probl Gen Genet 2:51–65

Markel AL, Borodin PM (1981) Genetiko-evolyutsionnye aspekty stressa (Genetic and evolutionary aspects of stress). In: Voprosy obshchey genetiki (Aspects of general genetics). In: Altukhov YP (ed) Proceedings of the XIV international congress of genetics. Moscow, Nauka, pp 262–271 (in Russian)

Markel AL, Trut LN (2011) Behavior, stress, and evolution in light of the Novosibirsk selection experiments. In: Gissis SB, Jablonka E (eds) Transformations of Lamarckism. From subtle fluids to molecular biology. MIT Press, Cambridge, pp 171–180

Markov AV (2000) Vozvrashchenie Chernoy Korolevy, ili zakon rosta sredney prodolzhitelnosti sushchestvovaniya rodov v protsesse evolyutsii (The return of the Black Queen, or the law of increase of mean duration of genera in the course of evolution). Zhurnal obshchey biologii 61:357–369 (in Russian)

Naumenko VS, Kozhemjakina RV, Plyusnina IZ, Popova NK (2009) Expression of serotonin transporter gene and startle response in rats with genetically determined fear-induced aggression. Bull Exp Biol Med 147:86–89

Nestler EJ (2012) Stress makes its molecular mark. Nature 4:171–172

Plyusnina IZ, Oskina IN (1997) Behavioral and adrenocortical responses to open-field test in rats selected for reduced aggressiveness towards man. Physiol Behav 61:381–385

Plyusnina IZ, Oskina IN, Tibeikina MA, Popova NK (2009) Cross-fostering effects on weight, exploratory activity, acoustic startle reflex and corticosterone stress response in norway gray rats selected for elimination and for enhancement of aggressiveness towards human. Behav Genet 39:202–212

Popova NK, Kulikov AV (1997) Avgustinovich DF, Voĭtenko NN, Trut LN Effect of domestication of the silver fox on the main enzymes of serotonin metabolism and serotonin receptors. Genetika 33:370–374

CAS   PubMed   Google Scholar  

Razumovsky SM (1981) Zakonomernosti dinamiki biogeotsenozov (Patterns in the dynamics of biogeocenoses). Nauka, Moscow, 231 pp (in Russian)

Robinson R (1965) Genetics of the Norway rat. Pergamon Press, Oxford 805

Schmalhausen II (1987) Factors of evolution: the theory of stabilizing selection. University of Chicago Press, Chicago, p 327

Shikhevich SG, Os’kina In, Plyusnina IZ (2003) Responses of the hypophyseal-adrenal system to stress and immune stimuli in gray rats selected for behavior. Neurosci Behav Physiol 33:861–866

Trapezov OV (2002) Domestikatsiya kak faktor koevolyutsii zhivotnykh i cheloveka (Domestication as a factor of coevolution animals and humans). Filosofiya nauki 2:86–101 (in Russian)

Trapezov OV (2008) Gomologicheskie ryady izmenchivosti okraski mekha u amerikanskoy norki ( Mustela vison Schreber, 1777) v usloviyakh domestikatsii (Homologous series in coat color variation in the American mink ( Mustela vison Schreber, 1777) under domestication). VOGiS Herald 11:547–559 (in Russ.)

Trapezov OV, Belyaev DK (1986) Svyaz selektsionnogo izmeneniya povedeniya s reproduktivnoy funktsiey amerikanskoy norki (An association between selection-induced behavioral changes and the reproduction function of the American mink). Zhurnal obshchey biologii 4:445–450 (in Russian)

Trapezov OV, Trapezova LI, Alekhina TA, Klochkov DV, Ivanov YuN (2009) Vliyanie mono- i diretsessivnosti po mutatsiyam, zatragivayushchim okrasku mekha, na uroven soderzhaniya monoaminov v mozge u amerikanskoy norki (Mustela vison Schreber) [Effects of the mono- and direcessivity of coat color mutations on the brain’s levels of monoamines in the American mink (Mustela vison Schreber)]. Genetika 45:1641–1645 (in Russain)

Trut LN (1988) The variable rates of evolutionary transformations and their parallelism in terms of destabilizing selection. J Anim Breed Genet 105:81–90

Trut LN (1999) Early Canid domestication: the farm-fox experiment. Am Sci 87:160–165

Trut LN (2001) Experimental studies of early Canid domestication. In: Ruvinsky A, Sampson J (eds) The genetics of the dog. CABI Publishing, NY, pp 15–42

Trut LN, Pliusnina IZ, Kolesnikova LA, Kozlova ON (2000) Interhemisphere neurochemical differences in the brain of silver foxes selected for behavior and the problem of directed asymmetry. Genetika 36:942–946

Trut LN, Plyusnina IZ, Oskina IN (2004) An experiment on fox domestication and debatable issues of evolution of the dog. Russ J Genet 40:644–655

Article   CAS   Google Scholar  

Trut L, Oskina I, Kharlamova A (2009) Animal evolution during domestication: the domesticated fox as a model. BioEssays 31:349–360

Vavilov NI (1967) Zakon gomologicheskikh ryadov v nasledstvennoy izmenchivosti (The law of homologous series in the inheritance of variability). In: Izbrannye proizvedeniya v dvukh tomakh (literally: Selected works in two volumes). Nauka, Leningrad 1:7–61 (in Russian)

Wilson AC (1985) The molecular basis of evolution. Sci Am 253:164–173

Zeder MA (2012) Pathways to animal domestication. In: Gepts P (ed) Biodiversity in agriculture: domestication, evolution, and sustainability. Cambridge University Press, Cambridge, pp 227–259

Zherikhin VV (1997) Osnovnye zakonomernosti filotsenogeneticheskikh protsessov (na primere nemorskikh soobshchestv mezozoya i kaynozoya) [Main patterns of phylocenogenetic processes (with Mesozoic and Cenozoic non-marine communities as examples)]. Thesis for Doctor of Science in the form of a scientific paper (in Russian)

Download references

Author information

Authors and affiliations.

Institute of Cytology and Genetics, SB RAS, Novosibirsk, Russia

Ludmila N. Trut, Yury E. Herbek, Oleg V. Trapezov, Sergey A. Lashin, Yury G. Matushkin, Arcady L. Markel & Nikolay A. Kolchanov

You can also search for this author in PubMed   Google Scholar

Corresponding author

Correspondence to Arcady L. Markel .

Editor information

Editors and affiliations.

Joint Institute for Nuclear Research, Dubna, Moscow Region, Russia

Victoria L. Korogodina

Department of Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada

Carmel E Mothersill

Genetics and Biotechnology, St. Petersburg State University, St. Petersburg, Russia

Sergey G. Inge-Vechtomov

Colin B. Seymour

Rights and permissions

Reprints and permissions

Copyright information

© 2016 Springer International Publishing AG

About this chapter

Trut, L.N. et al. (2016). The Animal Domestication Experiment as a Model of the Evolutionary Process: A New Insight into Evolution Under Selection Targeting Regulatory Systems. In: Korogodina, V., Mothersill, C., Inge-Vechtomov, S., Seymour, C. (eds) Genetics, Evolution and Radiation. Springer, Cham. https://doi.org/10.1007/978-3-319-48838-7_37

Download citation

DOI : https://doi.org/10.1007/978-3-319-48838-7_37

Published : 30 March 2017

Publisher Name : Springer, Cham

Print ISBN : 978-3-319-48837-0

Online ISBN : 978-3-319-48838-7

eBook Packages : Biomedical and Life Sciences Biomedical and Life Sciences (R0)

Share this chapter

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Publish with us

Policies and ethics

• Find a journal
• Track your research

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Scientific Reports

The scaling of social interactions across animal species

Luis e. c. rocha.

1 Department of Economics, Ghent University, Ghent, Belgium

2 Department of Physics and Astronomy, Ghent University, Ghent, Belgium

Jan Ryckebusch

Koen schoors.

4 Higher School of Economics, National Research University, Moscow, Russia

Matthew Smith

3 The Business School, Edinburgh Napier University, Edinburgh, UK

Associated Data

Social animals self-organise to create groups to increase protection against predators and productivity. One-to-one interactions are the building blocks of these emergent social structures and may correspond to friendship, grooming, communication, among other social relations. These structures should be robust to failures and provide efficient communication to compensate the costs of forming and maintaining the social contacts but the specific purpose of each social interaction regulates the evolution of the respective social networks. We collate 611 animal social networks and show that the number of social contacts E scales with group size N as a super-linear power-law E = C N β for various species of animals, including humans, other mammals and non-mammals. We identify that the power-law exponent β varies according to the social function of the interactions as β = 1 + a / 4 , with a ≈ 1 , 2 , 3 , 4 . By fitting a multi-layer model to our data, we observe that the cost to cross social groups also varies according to social function. Relatively low costs are observed for physical contact, grooming and group membership which lead to small groups with high and constant social clustering. Offline friendship has similar patterns while online friendship shows weak social structures. The intermediate case of spatial proximity (with  β = 1.5 and clustering dependency on network size quantitatively similar to friendship) suggests that proximity interactions may be as relevant for the spread of infectious diseases as for social processes like friendship.

Introduction

Social animals including humans live in groups to optimise the multiplicative benefits of social interactions such as protection, coordination, cooperation, access to information, and fitness, while balancing the competition, disease risk, and stress costs of group living 1 – 3 . Social interactions are fundamentally dyadic yet sufficiently diverse to link multiple animals or humans in connected social structures 1 , 4 , 5 . The purpose of social interactions is also diverse and spans a range of processes including communication, trust, grooming, dominance, or simply the loosely defined idea of friendship 1 , 4 , 6 . Correlations between social interactions, as for example dominance and physical contact, friendship ties maintained through communication, or the intertwined relation between trust and spatial proximity, reveal the complexity of social phenomena and suggest that common principles may underlie the formation of social ties.

A fundamental question concerns how the number of social connections depends on group size, and whether there are any emerging patterns in this relationship. The answer may reveal whether interaction patterns become more complex with size in order to maintain efficient social structures within the group. The cost to establish and maintain social contacts in small groups is relatively low but increases in larger groups 7 . This increasing costs leads to peer selection, either by necessity or affinity, up to a species-specific cognitive saturation point in the number of contacts one can manage 8 . Assuming that all members of a social group are reachable via social ties, in the limiting scenarios, a group of size N individuals may have a fragile star-like structure with E = N - 1 social ties to minimise social interactions (lowest cost) or a fully connected clique with E = N ( N - 1 ) / 2 ties (highest cost).

Evolutionary arguments support that social groups specialise and optimise social interactions to save resources while keeping or increasing the group efficiency 9 – 11 , as for example in response to predators (ecological conditions) 12 or to fitness 13 , 14 . There is also the argument that human social networks have an optimal size to optimise information transfer within groups 15 . Research on urban systems shows that human societies also organise in groups (e.g. cities) to optimise resources like infra-structure and to increase intellectual, social and economic outputs 16 , 17 . These observations lead us to hypothesise that across species and social contexts, the number of social contacts E scales with group size N as E = C N β , where C and β are positive constants.

Until recently, measuring social interactions was laborious. Past research relied on observations of animal and human behaviour or self-reporting of social contacts through questionnaires 4 . A natural limitation of these techniques is the size of the observed populations and potential recalling errors, as for example the inability to accurately identify or quantify each interaction 1 , 4 . Electronic devices (e.g. mobile phones 18 or proximity sensors 19 , 20 ) and online platforms now provide means for passive and accurate recording of spatio-temporal location, communication between animals and between humans, among other forms of animal or human interactions. State-of-the-art electronic data collection is scalable but its ability to detect authentic social interactions may be questioned and should be treated cautiously 21 , 22 .

We collate extensive data to show empirically that the number of social contacts scales super-linearly (i.e. β > 1 ) with group size and that social interactions can be categorised in different exponents β independently of the animal species. We provide evidence that this scaling is necessary to maintain fundamental complex network structures irrespective of existing group sizes. We also fit our data to a social network model and show that a multi-layer structure and the cost of crossing social layers may explain the estimated scaling exponents.

The data sets were collated using online databases of animal and human social networks previously analysed by other authors. All networks were reviewed for consistency and the data sets were standardised such that only unique pairs of social contacts were counted, i.e. self-loops, weighting, timings of contacts, and directions were removed. Social interactions were identified and labelled in the original studies by domain experts via direct observation (animal interactions), questionnaires (offline friendship), electronic devices (spatial proximity), and online platforms (online friendship) (see SI ). To minimise potential ambiguities, each network was constructed based on the specific definition of social interaction in the respective original study. Table  1 shows the number of networks for each type of social interaction and animal class, including captive and free-ranging animals. The network size varies across species and social interactions because of experimental settings, characteristics and limitations of the study populations, e.g. the observation capacity of researchers, cost of technical devices, free-range vs. confined animals, online platforms, or animals living in small groups (see SI ).

Number of networks for each type of social interaction and animal class.

In a total of 611 networks, there are 179 cases of human and 432 cases of non-human social interactions, including 281 captive and 151 free-ranging animals.

Scaling of social interactions

The networks of social interactions were grouped in categories following the type of social interactions as reported in the original studies (Table  1 ). Figure  1 shows the scaling between the number of social contacts E and size N (i.e. the number of interacting individuals) for each of the 6 original categories. We assume that the scaling of social relations is independent of species and test our hypothesis E = C N β by fitting a power-law to the data using logarithmic transformed variables to evenly distribute the data points:

The fitting exercise gives super-linear power-law exponents (i.e. β > 1 ) and strong linear correlations ( 0.55 < r < 0.99 ) for all categories of social interactions (Table  2 ). Assuming a small error ϵ in β ^ , the exponents follow the general law ( β = 1 + a / 4 ) with a ≈ 1 for online friendship ( ϵ = 12 % ), a ≈ 2 for spatial proximity ( ϵ = 4 % ), a ≈ 3 for group membership ( ϵ = 2.6 % ) and offline friendship ( ϵ = 5 % ), and a ≈ 4 for physical contacts ( ϵ = 1 % ) and grooming ( ϵ = 6 % ), despite differences in species and sample sizes (Fig.  1 ).

The number of social connections E versus the group size N across species. Empirical data (each symbol corresponds to a different species) and regression curves (dashed lines) for all 6 categories of social interactions: ( A ) physical contact ( β ^ A = 2.01 , 95 % CI [1.98, 2.04], n = 250 ); ( B ) grooming ( β ^ B = 1.94 , 95 % CI [1.53, 2.36], n = 23 ); ( C ) group membership ( β ^ C = 1.73 , 95 % CI [1.47, 1.99], n = 16 ); ( D ) spatial proximity ( β ^ D = 1.52 , 95 % CI [1.45, 1.59], n = 231 ), with 38 % human and 62 % non-human networks; ( E ) offline friendship ( β ^ E = 1.79 , 95 % CI [1.30, 2.29], n = 67 ); ( F ) online friendship ( β ^ F = 1.22 , 95 % CI [1.06, 1.37], n = 24 ). Details of the fitting in Table  2 . All axes are in log-scale.

Best fitting exponents for the 6 types of social interactions.

The variable n gives for each type of social interaction the number of different networks that was included in the fit. Orthogonal regression is used to account for measurement errors in both axes.

This super-linear scaling indicates increasing densification of social contacts, that is, larger social groups have on average more social contacts per-capita than the smaller ones. It is not surprising that β > 1 because the number of social connections must scale at least linearly with group size ( E ∝ N ) to maintain the social network connected; this is known as the percolation threshold in random networks 23 . If E ≈ N , small perturbations may fragment the network, breaking down the group structure. Furthermore, β > 1 suggests that a super-linear number of contacts are necessary to create and maintain the complex social network structures for the groups to function cost-efficiently irrespective of size.

Social network structure

We study the network structures for each of the six types of social interactions (see “ Methods ”). The clustering coefficient ⟨ c c ⟩ is a local measure of the level of sociality between common contacts of a focal individual (i.e. the fraction of social triangles). Its intensity indicates an evolutionary group advantage as for example fitness benefits 24 , 25 . Networks with higher clustering are relatively more robust since the deletion of a social connection would not significantly affect interaction and communication among close contacts. In our social networks, ⟨ c c ⟩ is constant for varying network size for all types of social contacts (Fig.  2 ). In random networks, the clustering coefficient decays with increasing network size as ⟨ c c ⟩ = ⟨ k ⟩ / N , where ⟨ k ⟩ is the average number of contacts (or edges) in the network 23 . The inset of Fig.  2 F shows the results for the randomised versions of the same online friendship networks (see SI for the other categories). In all categories, there is a higher clustering coefficient than expected on the basis of randomised social contacts (see caption Fig.  2 ). Since the average degree is defined as ⟨ k ⟩ = 2 E / N , we have ⟨ c c ⟩ = ⟨ k ⟩ / N = 2 E / N 2 and thus would need E ∝ N 2 to have constant clustering in random networks. Evolutionary theory implies that more complex structures may emerge in such social systems to optimise resources, e.g. to reap the fitness related benefits, and thus relatively less social contacts become necessary to reach the same level of clustering across group sizes 24 , 25 . For example, for some classes of random heterogeneous networks, ⟨ c c h ⟩ = A / N , where the proportionality constant A depends on the heterogeneity of the distribution of contacts among individuals and is lower than ⟨ k ⟩ 23 .

Network clustering structures. The average clustering coefficient ⟨ c c ⟩ between close contacts vs. network size for ( A ) physical contact (median values for the empirical M emp = 0.94 and randomised M rand = 0.88 versions of the same networks); ( B ) grooming ( M emp = 0.68 and M rand = 0.56 ); ( C ) group membership ( M emp = 0.79 and M rand = 0.69 ); ( D ) spatial proximity ( M emp = 0.50 and M rand = 0.22 ); ( E ) offline friendship ( M emp = 0.37 and M rand = 0.07 ); ( F ) online friendship ( M emp = 0.04 and M rand = 3.5 · 10 - 5 ); the inset is the distribution for the random version of the same networks. Dashed horizontal lines are the median values of the empirical networks. Log-binned (x-axes) Tukey box plots with diamonds representing outliers.

The average length of the shortest-paths ⟨ l ⟩ measures the average distance between any pairs of individuals in the social network and quantifies the communication potential between parts of the network 26 . Shorter average distances (i.e. ⟨ l ⟩ ≪ N , resulting in the small-world effect 27 ) indicate that information flows quickly over the network, which is a fundamental characteristic of efficient group organisation 28 . For physical contacts, grooming, and group membership, ⟨ l ⟩ is constant and slightly higher than one (Fig.  2 A–C). For spatial proximity and offline friendship, the values increase with size following quantitatively similar trends (Fig.  2 D,E). The results for online friendship suggest a constant trend (Fig.  2 F). In all cases, the average path-length is ⟨ l ⟩ < 6 , which is the small-world horizon observed empirically 23 . For all 6 categories, the random versions of the same networks give constant relations albeit generally with lower values (see SI ). In theoretical random networks, the average distance increases slowly with the network size as ⟨ l ⟩ ≈ log ( N ) / log ( ⟨ k ⟩ ) 23 . Nevertheless, the average path-length ⟨ l ⟩ is approximately constant across group sizes if E ∝ N β for β > 1 , since in this case ⟨ l ⟩ ≈ log ( N ) / log ( 2 N β - 1 ) ≈ 1 / ( β - 1 ) . Smaller β thus leads to higher ⟨ l ⟩ , as observed in the analysed networks. In some classes of heterogeneous random networks, ⟨ l ⟩ is also nearly constant with network size 23 . The density of contacts explains the low ⟨ l ⟩ for physical contact, grooming and group membership. The discrepancy of spatial proximity, offline and online friendship with the random case indicates that more complex network structures are being formed in larger groups for these types of social interactions. In sparse networks, like those, a high level of local clustering increases the distance between random pairs of network nodes because of local spots of connectivity redundancy 23 . Taken together, the constant clustering across network sizes (Fig.  2 ) implies that the average distance will necessarily increase (Fig.  3 ), unless followed by a sufficient increase in the number of connections (to maintain low average distances as the group increases). The growth in offline friendship followed by a seemingly constant pattern for online friendship (which has larger sizes) suggests a potential saturation in ⟨ l ⟩ for human friendship in line with the small-world horizon observed in previous studies 23 . Although communication remains efficient (because ⟨ l ⟩ ≪ N ), the benefits of forming larger groups do not compensate the costs of optimising certain network structures, as is the case for other types of social interactions involving physical contact.

Network path structures. The average shortest path-length ⟨ l ⟩ vs. network size in the networks of ( A ) physical contact (median values for the empirical M emp = 1.10 and randomised M rand = 1.05 versions of the original network); ( B ) grooming ( M emp = 1.39 and M rand = 1.29 ); ( C ) group membership ( M emp = 1.30 and M rand = 1.09 ); ( D ) spatial proximity ( M emp = 2.16 and M rand = 2.00 ); ( E ) offline friendship ( M emp = 3.19 and M rand = 3.36 ); ( F ) online friendship ( M emp = 4.66 and M rand = 4.97 ). Dashed horizontal lines are the median values of the empirical networks. Log-binned (x-axes) Tukey box plots with diamonds representing outliers.

Multi-layer model

Multi-layer models can be used to represent the underlying generative mechanisms through which individuals combine skills and affinity to build up more complex social groups. From single individuals to the entire population, individuals may be stratified in layers (or levels) corresponding to different groups 29 . For example, living in households (layer 1) within neighbourhoods (layer 2) that in turn are part of cities (layer 3), and so on, seems natural for humans. While people mostly interact with those in the same group (e.g. within the same household), interactions across groups are less frequent 30 (e.g. between different households in the same neighbourhood). Interactions across groups at the same layer are necessary to define higher-order groups, i.e. a group at the next higher layer, as for example a neighbourhood is a result of interactions between individuals from different households. Multi-layer models have been used to explain spatial relations in vascular 31 and infrastructure 17 systems. We argue that such models are also of value for social groups, not necessarily spatially bound, since multi-layer organisation has been observed across animal species in which a relation between group sizes in different layers vary from nearly 2.5 in primates to about 3 for other mammals including humans 14 , 32 . This means that individuals are organised as multiples of 3, for example, in groups of 5 (layer 1), 15 (layer 2), 45 (layer 3), and so on. The model detailed below does not aim to reproduce all structures of the 611 analysed networks but focuses on the scaling exponents β .

The self-similar multi-layer group structure is mathematically represented as a branching tree with a group at layer h split into b sub-groups at layer h - 1 (Fig.  4 ). At the highest layer h max , all individuals belong to a single social group, i.e. N = b h max , and at the lowest layer ( h min = 0 ), each group is formed by a single unique individual. In this model, individuals i and j make a social contact ( i ,  j ) with probability p Δ h ( i , j ) dependent on the distance Δ h between the layers that separate them. Closer individuals (e.g. at distance Δ h = 1 because they are living in the same neighbourhood or belonging to the same social group) are more likely to interact than individuals living far apart (e.g. at distance Δ h = 2 because they are living in different cities or belonging to different social groups), i.e. p Δ h ( i , j ) decreases with Δ h . The multi-layer tree-like structure only defines the distance Δ h between the groups that is in turn used to form contacts in the social network (Fig.  4 ); the resulting social network only has tree-like structure for sparse networks, i.e. when E ≪ N 2 . The self-similarity between layers implies that p Δ h ( i , j ) / p Δ h - 1 ( i , j ) = c o n s t 33 . A power-law of the form p Δ h ∝ c - Δ h , with c > 1 , satisfies this relationship. The parameter c represents the cost to make social interactions across layers, that we assume is lower than the cost to create a new layer, i.e. c < b , because multiple contacts are necessary to establish a new layer. For a given individual i , the expected number of social connections ⟨ e ⟩ i is:

For 1 ≤ c < b , the sum converges:

Since N = b h max and c h max = b h max log b ( c ) , we get:

Therefore, the total number of social connections is:

The multi-layer model implies that β = 2 - log b ( c ) . Assuming that b = 2.5 14 , the cost of connections is thus c A = 1 for physical contact ( β A ≈ 2 ), c B = 1 for grooming ( β B ≈ 2 ), c C = 1.26 for group membership ( β C ≈ 1.75 ), c D = 1.58 for spatial proximity ( β D ≈ 1.5 ), c E = 1.26 for offline friendship ( β E ≈ 1.75 ) and c F = 1.99 for online friendship ( β F ≈ 1.25 ). This cost is associated to crossing (virtual) barriers between social groups that might cause the creation of larger groups. The low cost ( c = 1 ) for physical contact and grooming means that p Δ h = 1 , i.e. the probability to form connections is independent of the social distance Δ h , collapsing the assumption of multi-layer structure. For such types of social interactions, the connections within the same social group are favoured; individuals do not groom in different social groups nor make persistent physical contacts, except physical contacts for conflict that would not be reflected in our data. This effect is related to the high clustering coefficient reported in previous sections and may explain the relatively small size of such networks. The number of social contacts for such activities is limited within the same social group.

Multi-layer social model. The underlying multi-layer structure (left) defines the probability p Δ h ( i , j ) ∝ c - Δ h of forming connections between individuals i and j in the social network (right). If c = 1 , everyone interacts with everyone else leading to a fully connected network whereas for higher c , interactions between closer individuals (lower h ) are more common. For example, the distance Δ h A , B = 1 and Δ h A , D = 2 . With cost c = 1 , edges ( A ,  B ) and ( A ,  D ) are equally likely ( p 1 = p 2 ∝ 1 ), whereas with higher cost, e.g. c = 2 , edge ( A ,  B ) is more likely ( p 1 ∝ 1 / 2 ) to occur than edge ( A ,  D ) ( p 2 ∝ 1 / 4 ).

Online friendship, on the other hand, is costly ( c ≈ 1.99 ) in terms of crossing social boundaries to connect individuals from different social groups 34 , e.g. with different tastes, ideas, location, age, and so on. Socially closer individuals would be favoured here as well since it is harder to be friends with dissimilar people than with those similar to each other 30 . However, given that online connections are cheap to establish and maintain (i.e. do not need nurturing and resources), the multi-layer structure becomes relevant with a non-negligible number of socially distant connections being formed. Furthermore, online friendship typically mixes (real) friends, acquaintances, relatives, and co-workers, each belonging to different social groups, with some individuals acting as social brokers. For example, online friendship is more easily established between those studying in the same school than at different schools; however, inter-school friendship is facilitated by the online platform, though socially costly (lack of face-to-face interactions, no common friends, building trust). For networks derived from mobile phone communication in urban populations, a scaling exponent β = 1.15 has been reported 35 – 37 . Such mobile communication data sets mix professional and personal relations which possibly also leads to higher costs in the sense of crossing social boundaries. In one study, a constant clustering coefficient has been also observed suggesting that similar underlying principles may explain the formation of such social or communication structures 37 . The multi-layer structure becomes less relevant for offline friendship ( c ≈ 1.32 ) that are typically more spatially constrained in our data. For example, students or prison inmates will report friendship with those around them. In schools, from where most of our data come from, the social structure is seen at the class and school layers only. Given experimental limitations, it is often not possible to report friends outside the study setting, which could reveal higher social layers, e.g. neighbourhood friends. It is possible that the exponent β for friendship is thus between what we estimated for offline and online friendship if all layers of friends and not only those in the same study setting were reported.

Our analysis finds an intermediate exponent ( β = 1.5 ) and cost ( c ≈ 1.58 ) for spatial proximity. Spatial proximity is a particular type of social interaction. Grooming, physical contact and human friendship are well-defined interactions identified, respectively, by observing joint activities or by directly inquiring individuals. However, spatial proximity interactions are measured by sensors or direct observation and capture a mixture of social situations. Spatial proximity might reflect affinity, trust and friendship between individuals and animals sharing the same space 30 , e.g. persistent spatial proximity between pairs of cows 38 , or behavioural or trait similarity, i.e. homophily, as for example friends visiting a museum 39 or health-care workers in hospitals 40 . On the other hand, spatial proximity interactions might simply reflect spatial constrains forcing individuals and animals to be in close proximity during periods of time, e.g. a group of visitors of an art exhibition 39 or confined animals 38 . Nevertheless, also in the later, affinity and trust are reflected in the proximity contacts. As discussed above, it is possible that friendship at the society layer likely follows patterns intermediate to those observed in the online ( β = 1.25 ) and offline ( β = 1.75 ) categories. The existing literature associating friendship to time that individuals spent together 30 and the observation that spatial proximity contacts follow an intermediate exponent ( β = 1.5 ) suggest a potential link between these social interactions. We cannot make a strong association between the two types of social interactions due to lack of data of offline friendship in larger populations. Previous modelling exercises in urban populations suggest that β B = 1.5 can be explained by mobility ( H = 2 , where H is the Hausdorff dimension of a path in space) over two dimensional ( D = 2 ) spaces based on the assumption that fully-mixed populations may fully explore a given area 17 . While this assumption may hold within, e.g. schools, museums or barns, it does not apply on larger spatial areas since humans and animals are territorial and tend to spend most of time within certain locations 41 or with certain individuals 30 . On the other hand, the same model suggests that contacts per-capita scale as 0.25 (i.e. β = 1.25 ) under the same conditions (i.e. H = D = 2 ). This fits well to our findings for offline friendship, where people may virtually explore the whole social space and potentially interact with different individuals.

Conclusions

Our findings reveal key aspects of the organisation of animal social networks. Though primates and non-primates (including humans) are more represented than other animals in our data set, the universal scaling relations E = C N β between the number of social contacts E and size N suggest common organisation principles across animal species that can be explained by multi-layer models designed to maintain the functioning of the social groups 14 , 32 . Different scaling exponents following the general relation β = 1 + a / 4 , with a ≈ 1 , 2 , 3 , 4 allow us to distinguish types of social interactions and to infer network structures underlying those interactions. For all types of social interactions, the local clustering remains constant for increasing network sizes albeit having different intensity in each case. Physical contacts, grooming and group membership have similar constant median values that are higher than observed for spatial proximity, offline and online friendships. The average path-length is also constant and follow the small-world pattern (i.e. ⟨ l ⟩ ≪ N ) for most cases with the exception of spatial proximity and offline friendship where a quantitatively similar positive trend is observed with values below the small-world horizon of ⟨ l ⟩ ≈ 6 previously observed in social networks 23 .

One may argue that humans differ from other animals by developing more efficient social network structures, with relatively less contacts for larger network sizes, and thus lowering the scaling exponents. There is a quantifiable relationship with brain and group sizes, along with the complexity of the interactions. Humans are able to process the cognitive demand of other forms of relationships such as friendship, rather than mating and dominance relations that often occur within other animals and species 42 . The common scaling pattern observed across species and particularly for spatial proximity weakens the hypothesis that animals differ. Our results suggest that the type of social interaction, and to a lesser extent, the group size, are more relevant to determine the scaling exponents than the animal species. We reached this conclusion by combining data from different species. More statistical power could be achieved with a larger sample of network data for specific combinations of social interactions and species in order to study these relations separately. Given the multi-layer structure of social networks and experimental constraints, offline friendship data sets are limited to relatively small social circles 30 . If one could map higher social layers, the scaling exponent could decrease, likely to the same value as observed for spatial proximity. If this is confirmed in future studies, we will be able to infer that spatial proximity is a proxy of friendship across animals species 30 .

Physical contact, grooming and group membership are associated with more robust and topologically efficient networks (since clustering is higher and path-lengths are shorter) than friendship and proximity interactions. This social cohesion is a result of homophily and coordination to maintain group functioning, which likely creates smaller groups in these categories relative to friendship and proximity categories because of the cost of nurturing contacts. The frequency and number of social interactions leading to stable social contacts are also important to regulate diffusion processes such as communication 26 , innovation 16 , 17 , infectious diseases 19 , 43 and social phenomena 30 , 44 . Our results suggest that physical contacts and grooming are more efficient than proximity to facilitate spread phenomena at the population (network) level. Online friendships are associated to looser social structures easier to fragment as the groups increase in size. The relatively high cost of nurturing too many online social contacts across social layers restrains the opportunities to generate higher clustering or common friends, and create redundant structures, as observed in the smaller networks related to activities necessary to keep the group functioning.

Although we focus on temporally stable social networks 45 , the availability of temporal information and intensity of certain social interactions could also help to understand the formation and dissolution of social contacts and how particular network structures are formed. Future research should add a quality measure to social interactions (e.g. via weights or temporal dynamics) to investigate the varying importance of creating and maintaining particular structures 46 . Strong super-linear scaling implies prohibitive social costs to maintain larger groups for some types of social interactions. The questions on whether there is a maximum or optimal group size in which efficient groups can exist and fitness is maximised 47 , or whether more complex network structures are necessary to sustain larger groups, remain open.

The data sets used in this study were collected using public network data repositories. A list of repositories and a full list of the original references for the 611 data sets are available in the SI . The 6 types of social interactions: physical contact, grooming, group membership, spatial proximity, offline friendship and online friendship were identified and labelled in the original studies by domain experts via direct observation (animal interactions), questionnaires (offline friendship), electronic devices (spatial proximity), and online platforms (online friendship). All 611 networks were standardised for the analysis, including the removal of self-loops, edge directions, and edge weights.

A network G of size N is defined as a set of N nodes i and a set of E edges ( i ,  j ) connecting nodes i and j . A node represents either a person or an animal. An edge represents a social connection of a specific type. In an undirected network, edges are reciprocal, i.e. ( i , j ) = ( j , i ) . In a network without self-loops, there is no edge ( i ,  i ).

The clustering coefficient of a node i is given by:

where e i is the number of edges (connections) between the n i nodes directly connected to node i . The average clustering coefficient of the network G is thus:

The topological distance between the nodes i and j is the length of the shortest-path l ij in number of edges. It is calculated within the largest connected component of the network G . In the largest connected component, there is at least one path between any pairs of nodes i and j . The average shortest-path length is:

Supplementary Information

Acknowledgements.

The authors thank Luana de Freitas Nascimento for helpful discussions.

Author contributions

L.R. designed the research, made the analysis and wrote the draft; J.R., K.S., M.S. contributed with methods; All authors revised the manuscript.

Competing interests

The authors declare no competing interests.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

The online version contains supplementary material available at 10.1038/s41598-021-92025-1.

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

13.1: Introduction to Animal Reproduction

• Last updated
• Save as PDF
• Page ID 46229

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

What you’ll learn to do: Discuss methods and features of animal reproduction

Most animals are diploid organisms, meaning that their body (somatic) cells are diploid and haploid reproductive (gamete) cells are produced through meiosis. Some exceptions exist: for example, in bees, wasps, and ants, the male is haploid because it develops from unfertilized eggs. Most animals undergo sexual reproduction. This fact distinguishes animals from fungi, protists, and bacteria, where asexual reproduction is common or exclusive. However, a few groups, such as cnidarians, flatworm, and roundworms, undergo asexual reproduction, although nearly all of those animals also have a sexual phase to their life cycle.

Contributors and Attributions

• Introduction to Animal Reproduction. Authored by : Shelli Carter and Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution
• Biology. Provided by : OpenStax CNX. Located at : http://cnx.org/contents/[email protected] . License : CC BY: Attribution . License Terms : Download for free at http://cnx.org/contents/[email protected]

• Opening hours
• Entrance price
• Place to eat
• Gift and Souvenir Shops
• Information for people with reduced mobility (PRM)
• About the foundation
• Our projects
• Get involved
• Become a volunteer

Helping giant pandas in ensuring offspring

Fragments of forest as habitat.

Giant pandas once inhabited a vast territory in southern and eastern China. However, their original forests have been largely transformed by human activities for agriculture or forestry. The result? The species now only survives in small forest areas scattered across 6 mountain ranges in Southwest China. There are currently 1,864 giant pandas remaining in the wild. This fragmented habitat isolates giant panda populations from each other. This prevents them from breeding with each other and thus reduces the genetic diversity of the species.

A challenging reproduction

If the destruction of its habitat already makes the situation of the giant panda precarious, this is further exacerbated by a rather erratic reproduction. Indeed, the female is fertile only 1 to 3 days per year! Pregnancy is then complex, with a period of diapause during which the development of the embryo “pauses”, pseudo-pregnancies that are practically impossible to distinguish from “real” pregnancies, and sometimes loss of the fetus at the end of the pregnancy. The mechanisms behind these particular phenomena are largely still mysterious at present.

Why do they need our help? 

In addition to protecting its natural habitat, giant panda reproduction is a crucial issue for species conservation. In zoos, improving reproductive success contributes to producing a greater number of young pandas, which may eventually be reintroduced into the wild. Furthermore, knowledge of each individual’s genetic heritage enables the formation of pairs in a way that maximizes genetic diversity. In the long term, the insights gained from monitoring giant panda reproduction in zoos will benefit the monitoring of their wild counterparts’ reproduction.

What does the Pairi Daiza Foundation do?

The Pairi Daiza Foundation has supported a scientific research project from 2018 to 2021, led by Dr. Jella Wauters, a researcher at the Faculty of Veterinary Medicine of Ghent University. The main objectives were:

• Developing “pregnancy tests” to confirm gestation;
• Discovering the signals that regulate embryo diapause;
• Accurately predicting the fertile period and parturition.

On a daily basis, these studies involved collecting urine and fecal samples to measure biomarkers (including hormones), as well as long hours of observing the behavior of female giant pandas and closely monitoring their weight and digestion.

An international conservation program

The giant panda has been globally protected for over 30 years by an international conservation program established by China. This is manifested in a global breeding program (in which Pairi Daiza and its Foundation have been participating since 2014), as well as in the restoration of their habitat, the establishment of reserves, and the creation of corridors for them to move from one reserve to another. This is a long-term effort and a multidisciplinary commitment that is bearing fruit. From 1,200 in the 1980s, the population of wild giant pandas has now risen to over 1,800! Efforts must, of course, be continued.

Become a Pairi Daiza Member

From 105 euros/year.

Enjoy Pairi Daiza as many times as you like, with its gardens changing with the seasons and its activities, for 365 days, with the exception of the few days it’s closed in January and February. And enjoy many other benefits and discounts!

• Pairi Daiza L.L.C.
• Pairi Daiza Experiences
• Pairi Daiza Resort
• Our mission
• General Data Protection Policy
• Cookie Policy
• For families
• For companies
• For schools

Pairi Daiza

Domaine de Cambron 7940 Brugelette Belgique

+32 (0) 68 250 850 [email protected]

Our applications

Subscribe to our newsletter

• Pairi Daiza Regulations
• > Cookies settings

Copyright © Pairi Daiza 2024

• Biotechnology
• Biochemistry
• Microbiology
• Cell Biology
• Cell Signaling
• Diversity in Life Form
• Molecular Biology
• Asexual Reproduction In Plants
• Types of Asexual Reproduction
• How Animals Reproduce?
• Difference Between Sexual And Asexual Reproduction
• How Reproduction is Happening in Humans?
• Reproductive Health Class Notes Biology
• What is Reproduction?
• Sexual Reproduction: An Overview
• Sexual Reproduction in Plants
• Chasmogamy - Examples and Reproductive Mechanism
• NCERT Notes for Class 8 Science Chapter 6: Reproduction in Animals
• Migration in Animals, Birds, and Fishes
• NCERT Solution for Class 8 Science Chapter 6 Reproduction in Animals
• Infertility of Reproductive Health Biology Class 12
• Reaching The Age Of Adolescence - Reproductive Health
• Diagram of Female Reproductive System
• Gemmule - Formation, Structure and Role in Sponge Reproduction
• Which is a Better Mode of Reproduction & Why?
• Diagram of Male Reproductive System

Asexual Reproduction in Animals

Asexual reproduction in animals involves the production of offspring without the involvement of gametes (sperm and egg). Common methods include budding, fragmentation, and parthenogenesis. Some invertebrates, such as starfish, flatworms, and certain species of insects, utilize asexual reproduction as a means of population growth and survival in stable environments.

It results in rapid population growth and colonization of new habitats without the need for a mate. However, it limits genetic variation, making populations susceptible to environmental changes. In this article, we will study Asexual Reproduction Animals, including their features and types, with examples.

Types of Asexual Reproduction in Plants

Table of Content

• What is Asexual Reproduction in Animals?

Features of Asexual Reproduction

Examples of asexual reproduction in animals , new mexico whiptail lizards, planarian flatworms, types of asexual reproduction , binary fission, fragmentation, parthenogenesis, advantages of asexual reproduction, disadvantages of asexual reproduction, conclusion: asexual reproduction animals, what is asexual reproduction in animals .

Asexual reproduction in animals involves the production of offspring without the fusion of gametes (sperm and egg). Various methods include budding, where a new organism grows as an outgrowth of the parent; fragmentation, where an organism breaks into pieces, each capable of regenerating into a new individual; and parthenogenesis , where unfertilized eggs develop into offspring. This process allows for rapid population growth and colonization of new habitats but limits genetic diversity, reducing adaptability to changing environments.

Features of Asexual Reproduction are:

• Lack of Gametes: Asexual reproduction doesn’t involve the fusion of gametes (sex cells) from two parents.
• Single Parent: Offspring are produced from a single-parent organism.
• Genetic Uniformity: Since only one parent is involved, offspring are genetically identical to the parent, resulting in clones.
• Rapid Reproduction: Asexual reproduction allows for rapid population growth.
• Common in Simple Organisms: Asexual reproduction is common in simpler organisms like bacteria , yeast, and some plants and animals.
• Mitosis: Cell division occurs through mitosis, where a parent cell divides into two identical daughter cells.
• Lack of Genetic Variation: Since offspring are genetically identical to the parent, there’s limited genetic variation within populations undergoing asexual reproduction.
• Clonal Colonies: Asexual reproduction can lead to the formation of clonal colonies, where interconnected individuals arise from the same parent.

Some examples of asexual reprodutcion in animals are:

Bacteria reproduce asexually through a process called binary fission , where a single parent cell divides into two identical daughter cells. This rapid form of reproduction contributes to their ability to quickly develop antibiotic resistance.

Binary Fission in Bacteria

All New Mexico whiptail lizards are females and can reproduce independently. They reproduce through a process called parthenogenesis, where eggs develop into offspring without fertilization by a male gamete. This unique reproductive strategy has allowed them to form a self-sustaining population.

Hydra, a freshwater organism, reproduces asexually through budding . A small bud develops on the body of the parent and detaches to form a new individual. This process allows for rapid population growth in favorable conditions.

Planarian flatworms are capable of regenerating lost body parts, allowing them to reproduce asexually through fragmentation . If a flatworm is cut into pieces, each fragment has the potential to regenerate into a complete organism, resulting in multiple offspring from a single parent.

Planaria Reproducing Asexually

Aphids, small insects that feed on plant sap, reproduce asexually through a process called parthenogenesis. Female aphids can produce offspring without mating with a male, allowing for rapid population growth under favorable environmental conditions.

Asexual reproduction includes several distinct mechanisms by which organisms can produce offspring without the need for gametes (sex cells) or mating. The main types of asexual reproduction are:

• Common in single-celled organisms like bacteria and protists.
• Parent cell divides into two identical daughter cells.
• Each daughter cell receives a copy of the genetic material.
• Rapid method of reproduction contributing to bacterial population growth.
• Genetic uniformity among offspring as they are clones of the parent.
• Simple binary fission (e.g., amoeba )
• Longitudinal binary fission (e.g., flagellates like Euglena)
• Transverse binary fission (e.g., Paramecium, Planaria, Diatoms, bacteria)
• Oblique binary fission (e.g., Cerium).
• Found in multicellular organisms like Hydra, yeast, and some plants.
• Parent organism produces a small outgrowth or bud.
• The bud gradually develops into a new individual.
• The bud detaches from the parent to live independently.
• Offspring are genetically identical to the parent organism.
• Exogenous/external budding (bud grows on the surface and detaches)
• Endogenous/internal budding (buds formed within the parent’s body, e.g., some marine sponges)
• Strobilation (repeated budding forming segments, e.g., Aurelia).
• Observed in certain animals like planarian flatworms.
• Parent organism breaks into fragments, each capable of developing into a new individual.
• Regeneration occurs from each fragment, forming multiple offspring.
• Each offspring retains genetic similarity to the parent organism.
• Fragmentation helps in rapid reproduction and colonization.
• Seen in various animals including insects (e.g., aphids), reptiles (e.g., some lizards), and fish.
• Females produce offspring without fertilization by a male.
• Eggs develop into embryos without genetic contribution from a male gamete.
• Offspring are genetically identical to the mother.
• Commonly occurs in environments with limited access to mates.

Advantages of Asexual reproduction includes:

• Asexual reproduction is faster than sexual reproduction because it does not require the complexities of mating and the production of gametes.
• Organisms can rapidly increase their population size under favorable conditions, as each individual can produce offspring independently.
• Offspring are genetically identical to the parent, ensuring uniformity in traits and adaptations that are well-suited to stable environments.
• Asexual reproduction eliminates the need to find a mate, which can be challenging in some environments or for organisms with low population densities.
• Organisms do not need to invest energy in finding mates or producing specialized reproductive structures like flowers or courtship displays.
• Asexual reproduction allows organisms to quickly colonize new habitats or recover from disturbances, as they can reproduce rapidly without waiting for specific environmental cues.
• Since there is no need to produce and maintain specialized reproductive organs, more energy and resources can be allocated to growth, survival, and other activities.
• If a parent organism possesses favorable traits for survival and reproduction, asexual reproduction allows for the direct transmission of these traits to offspring without dilution through genetic recombination.

Also Read: Genetic Diversity

Disadvantages of Asexual Reproduction are:

• Offspring produced through asexual reproduction are genetically identical to the parent, leading to reduced genetic diversity within populations.
• This limits their ability to adapt to changing environments and increases susceptibility to diseases and environmental stressors.
• Mutations that occur in the parent organism can be passed on to all of its offspring, leading to the accumulation of harmful genetic mutations over successive generations.
• Lack of genetic diversity makes populations less resilient to environmental changes, such as fluctuations in temperature, availability of resources, or the introduction of new predators or pathogens.
• Asexual reproduction restricts the ability of organisms to undergo evolutionary changes through genetic recombination and natural selection , as there is no mixing of genetic material from different individuals.
• Continuous reproduction through asexual means can lead to inbreeding depression, where deleterious recessive alleles become more prevalent in the population, resulting in reduced fitness and reproductive success.
• Organisms that depend on asexual reproduction may become dependent on specific environmental conditions or resources, making them vulnerable to changes in their habitat or the loss of key resources.
• In populations where asexual reproduction is common, individuals may compete more directly with their genetic clones for resources, leading to increased competition and potentially reduced overall fitness.

In conclusion, asexual reproduction in animals offers advantages such as rapid population growth and colonization of new habitats without the need for a mate. However, it limits genetic diversity, reducing adaptability to changing environments. Various methods like budding, fragmentation, and parthenogenesis enable animals to reproduce asexually, resulting in offspring genetically identical to the parent. Despite its drawbacks, asexual reproduction is a common strategy observed in organisms inhabiting stable environments or exhibiting rapid growth strategies.

Also Read: How Animals Reproduce – Sexual and Asexual Reproduction Types of Asexual Reproduction Asexual Reproduction in Plants 

FAQs on Asexual Reproduction Animals

What animals have asexual reproduction.

Animals such as certain species of bacteria, protozoans like amoeba, and invertebrates like planarians and some insects exhibit asexual reproduction.

What are the 7 Types of Asexual Reproduction in Animals?

The seven types of asexual reproduction in animals include binary fission, fragmentation, budding, parthenogenesis, gemmules, regeneration, and strobilation.

What is the Process of Binary Fission and What are its Drawbacks?

Binary fission is a form of asexual reproduction where an organism divides into two equal parts; its drawbacks include limited genetic variation and susceptibility to environmental stressors.

What is External Fertilization in Animals?

External fertilization in animals occurs outside the body, typically in water, where eggs and sperm are released and fertilization takes place externally.

 What is Natural Vegitative Propagation ?

Natural vegetative propagation is a form of asexual reproduction in plants where new individuals grow from vegetative parts such as roots, stems, or leaves.

 What is Sporogenesis in plants?

Sporogenesis in plants is the process of producing spores through meiosis in sporangia, leading to the formation of reproductive structures like pollen grains and spores.

Please Login to comment...

Similar reads.

• School Biology
• School Learning

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

• Search Menu
• Sign in through your institution
• Advance articles
• Editor's Choice
• Author Guidelines
• Submission Site
• Reasons to Publish
• Open Access
• About the European Society of Human Reproduction and Embryology
• Editorial Board
• Advertising and Corporate Services
• Journals Career Network
• Self-Archiving Policy
• Journals on Oxford Academic
• Books on Oxford Academic

Article Contents

Introduction, materials and methods, supplementary data, data availability, acknowledgements, authors’ roles, conflict of interest, in vivo effect of vaginal seminal plasma application on the human endometrial transcriptome: a randomized controlled trial.

• Article contents
• Figures & tables
• Supplementary Data

Laura Catalini, Mark Burton, Dorte L Egeberg, Tilde V Eskildsen, Mads Thomassen, Jens Fedder, In vivo effect of vaginal seminal plasma application on the human endometrial transcriptome: a randomized controlled trial, Molecular Human Reproduction , Volume 30, Issue 5, May 2024, gaae017, https://doi.org/10.1093/molehr/gaae017

• Permissions Icon Permissions

Studies in humans and animals suggest that seminal plasma, the acellular seminal fluid component, stimulates the endometrium to promote immune tolerance and facilitate implantation. We designed a randomized, double-blinded, placebo-controlled trial to investigate changes in the endometrial transcriptomic profile after vaginal application of seminal plasma. The study participants were randomized into two groups. Five women received a vaginal application of seminal plasma, and four received a placebo application with saline solution. The application was performed 2 days after HCG-triggered ovulation in an unstimulated cycle. After 5–8 days, an endometrial biopsy was collected to analyze differences in the endometrial transcriptomic profile using microarray analyses. A differential gene expression analysis and a gene set analysis were performed. The gene set enrichment analysis showed a positive enrichment of pathways associated with the immune response, cell viability, proliferation, and cellular movement. Moreover, pathways involved in implantation, embryo development, oocyte maturation, and angiogenesis were positively enriched. The differential gene expression analysis, after adjusting for multiple testing, showed no significantly differentially expressed genes between the two groups. A comparative analysis was also performed with similar studies conducted in other animals or in vitro using human endometrial cells. The comparative analysis showed that the effect of seminal plasma effect on the endometrium is similar in pigs, mice, and in vitro human endometrial cells. The present study provides evidence that seminal plasma might impact the endometrium during the implantation window, with potential to affect endometrial receptivity and embryo development.

Despite the great advancements in ART, the low Implantation rate is still a critical limiting factor. In particular, poor endometrial receptivity is considered a major cause of implantation failure, and its improvement is fundamental to further increase the success rate of treatments ( Fatemi and Popovic-Todorovic, 2013 ).

A correctly timed interaction between a viable embryo and a receptive endometrium is required for successful implantation ( Massimiani et al. , 2019 ). During the menstrual cycle, the endometrium goes through several morphological and functional changes and exhibits only a short period of receptivity, known as the implantation window, spanning between Days 20 and 24 of the menstrual cycle ( Achache and Revel, 2006 ; Diedrich et al. , 2007 ).

Estrogen and progesterone are the major players in the endometrial transition toward the receptive phase ( Marquardt et al. , 2019 ; Paria et al. , 2000 ). However, additional factors derived from semen might play a role in this transition ( Schjenken and Robertson, 2020 ). For example, it has been suggested that seminal plasma, the acellular seminal fluid component, stimulates the endometrium to promote immune tolerance and facilitate implantation ( Robertson and Sharkey, 2016 ). Experiments in mice, livestock animals, and in vitro studies in human endometrial cells have demonstrated that seminal plasma induces substantial transcriptomic changes related to cell migration, proliferation, and viability, as well as the immune response ( Chen et al. , 2014 ; Schjenken et al. , 2015 ; Martinez et al. , 2019 ; Bogacki et al. , 2020 ). Moreover, an in vitro study on human endometrial stromal fibroblasts showed that seminal plasma promoted decidualization ( George et al. , 2020 ).

The function of seminal plasma in reproduction is highly conserved through evolution ( Schjenken and Robertson, 2020 ). Indeed, it is involved in at least five important reproductive processes: (i) delivery and nourishment of spermatozoa; (ii) uterine removal of superfluous sperm and microorganisms introduced at mating; (iii) induction of alloimmunization: maternal tolerance towards paternal antigens to protect the fetus; (iv) tissue remodeling associated with endometrial receptivity and decidualization; and (v) stimulation of preimplantation embryo development ( Schjenken and Robertson, 2020 ). However, there might be some variations in the reactions elicited by seminal plasma across different species, influenced by the reproductive strategy and anatomy of the female reproductive system. For example, in humans, seminal plasma is delivered in the vaginal vault, and it mainly contacts and directly stimulates the ectocervix ( Sharkey et al. , 2012 ), while in other species, like mice and pigs, seminal plasma directly accesses the uterine cavity ( Schjenken and Robertson, 2020 ).

Routinely, only the spermatozoa are used during ART, while the remaining seminal fluid is eliminated. However, interest in seminal plasma has grown in recent years, and several studies, both in human and animal models, have been performed to investigate its role in implantation and pregnancy development ( Robertson, 2007 ; Crawford et al. , 2015 ; Ata et al. , 2018 ; Saccone et al. , 2019 ). Experiments in mice and livestock animals have shown increased implantation and pregnancy rates after exposure to seminal plasma ( Johansson et al. , 2004 , O’Leary et al. , 2004 , 2006 ). Human ART trials of seminal plasma application around ovulation are promising but not conclusive and more studies have to be performed ( Bellinge et al. , 1986 ; Qasim et al. , 1996 ; Tremellen et al. , 2000 ; Aflatoonian et al. , 2009 ; von Wolff et al. , 2009 ; Chicea et al. , 2013 ; Friedler et al. , 2013 ; von Wolff et al. , 2013 ; Mayer et al. , 2015 ). Two meta-analyses have critically evaluated these studies, demonstrating that seminal plasma exposure significantly improves the clinical pregnancy rate. The live birth rate is also increased but without reaching statistical significance, primarily due to the limited number of studies examining this outcome and the insufficiently large study populations ( Crawford et al. , 2015 ; Saccone et al. , 2019 ). A Cochrane review, including two supplementary studies, corroborated these observations. However, it also pointed out that the quality of evidence was low and suggested additional studies to support this preliminary evidence ( Ata et al. , 2018 ). It is important to note that 4 of the 11 studies included used the whole seminal fluid, while the other 7 only used the seminal plasma fraction.

This study aimed to investigate endometrial transcriptomic changes during the implantation window induced by vaginal application of seminal plasma. We hypothesized that seminal plasma application increases endometrial receptivity, modulating the female immune system. Since no other transcriptomic studies have been performed in humans, we compared our results with similar studies in other animals and in vitro ( Chen et al. , 2014 ; Schjenken et al. , 2015 ; Martinez et al. , 2019 ; Bogacki et al. , 2020 ).

Study design and setting

This was a single-center, two parallel-groups, 1:1 ratio, randomized, double-blinded, placebo-controlled clinical trial conducted at the fertility clinic, Odense University Hospital, Denmark, from 2020 to 2023.

Data management

The project was approved by the Scientific Ethics Committee (Project-ID: S-20190157) and the Data Protection Agency (Journal number 20/5793) of the Region of Southern Denmark. The project was also registered in ClinTrials.Gov (NCT ID: 04286425) on 24 February 2020.

All the sensitive data collected during the study were stored in the Redcap database via OPEN's server (Odense patient data exploration network), which was also used for the randomization process. The first patient was enrolled on 28 August 2020.

Participants

Women without a male partner undergoing gonadotropin-releasing hormone agonist long protocol treatments at our clinic from 2020 were eligible for this study. Inclusion criteria were no male partner and age between 20 and 40 years old. The exclusion criteria were: abnormal concentrations of FSH (normal range 3–9 IU/l); genital infections; severe endometriosis; severe polycystic ovarian syndrome; and chronic metabolic, immune, and/or neurocognitive diseases. Information was collected from their medical history and journal records.

Women with a male partner were excluded from this study to reduce the confounder effect of the partner’s seminal plasma. To be assessed for eligibility, women had to give their written informed consent.

Intervention

Eligible patients were randomly divided into two groups: a group receiving vaginal application of seminal plasma and a control group receiving a placebo saline solution application.

The patients received two applications of seminal plasma or placebo on two occasions during two consecutive cycles. The second application was the same type as the first application ( Fig. 1 ).

Intervention schedule.

The first application was performed during an unstimulated cycle the month before the scheduled IVF treatment, 2 days (36 h) after ovulation was triggered by an injection of HCG. The patients were monitored via transvaginal ultrasound, and ovulation was triggered by HCG administration when at least one follicle reached a diameter of >18 mm.

An endometrial biopsy was collected for analysis 5–8 days after the seminal plasma or placebo application.

The second application was made at the same time in the cycle as the first application, immediately after oocyte retrieval following GnRH agonist long protocol stimulation. The second application was offered only for the benefit of the patients. No tissue was collected for analysis after this application.

The study’s primary outcome was evaluation of the endometrial transcriptomic profile after vaginal seminal plasma application. The planned secondary outcome was a measure endometrial leukemia inhibitory factor (LIF) concentration.

Sample size

Since no comparable studies were available, the sample size was calculated according to changes in endometrial LIF concentration. LIF was selected as a reference for its role in the modulation of endometrial receptivity ( Salleh and Giribabu, 2014 ). We hypothesized no change in LIF concentration after application of placebo solution, 0 pg/ml (estimated standard deviation ≈5 pg/ml) and a change in LIF concentration between 6 and 15 pg/ml (estimated standard deviation ≈7 pg/ml) after application of seminal plasma. Given a type I error of 5% and a power of 80%, 20 women per group were needed to detect the least change in concentrations.

We based our estimation from the observation made by Comba et al. (2015) , in which the LIF concentration was compared between women with recurrent pregnancy loss and fertile women.

Randomization and blinding

The allocation list was created using https://sealedenvelope.com/ with block randomization method with random variables blocks of 4 and 6 and no stratification. To each allocation outcome, a random three-character alpha-numerical code was given to conceal the allocation until intervention. At the time of intervention, the application type was listed A or B and Identical CBS High-Security Sperm Straws (CryoBioSystem, L'Aigle, France) were used for seminal plasma and placebo. Only at the end of the data analysis, the application type was unblinded.

With this setting, the participants and the clinic personnel who performed the procedures and analyzed the data were blinded for the application type. The random generated allocation sequence was created by the responsible data manager at OPEN (Open Patient data Explorative Network). The participants were enrolled by the research nurse at the fertility clinic supported by the researcher following the project that also assigned the participant to the intervention.

Seminal plasma/placebo preparation and application

Seminal plasma was provided by the European Sperm Bank. To reduce variability, seminal plasma samples from four different donors were pooled together to reach the required amount to treat all women in the study.

Seminal plasma was collected from donors with normal sperm parameters who had consented to their semen being used for research purposes.

Seminal plasma was isolated from semen by centrifugation (3000 g , 10 min) followed by filtering through first a 1.2-µm filter (Sarstedt, Helsingborg, Sweden) and next a 0.45-µm filter. Samples were stored in the fridge at 4°C for 7–14 days before pooling. After being pooled together, the seminal plasma was further filtered through a 0.2-µm filter and checked by microscopy for the absence of cells. CBS High-Security Sperm Straws were filled with 500 μl of seminal plasma and kept in liquid nitrogen until use. Seminal plasma was released only after Nucleic Acid Amplification Testing to exclude HIV1, HIV2, Hepatitis B, Hepatitis C, Syphilis, Chlamydia, and Gonorrhea. Donors’ risk behavior and travel history were recorded at every donation. Moreover, from 2020, extra precautions concerning sperm donation and COVID-19 were implemented following the guidelines issued by the Danish Patient Safety Authority ( https://en.stps.dk/covid-19 ) and European Centre for Disease Prevention and Control ( https://www.ecdc.europa.eu/en/covid-19 ).

Sterile saline solution was used as a placebo solution. CBS High-Security Sperm Straws were filled with 500 μl of saline solution and kept in liquid nitrogen until use.

The CBS High-Security Sperm Straws containing seminal plasma/placebo solution were thawed 30 min before application. Then for the last 10 min before application, the samples were kept at 35°C. A FLEXI IUI catheter (Allwin Medical Devices, Anaheim, CA, USA) was used to apply 500 μl of seminal plasma/placebo solution in the posterior fornix and vaginal vault.

Endometrial biopsy collection

The endometrial biopsy was collected 5–8 days after the first seminal plasma or placebo application.

The endometrial biopsy was obtained using a curette with Vacu-Lok syringe (CooperSurgical, Trumbull, CT, USA) inserted into the uterus and scratching the uterine lining. The procedure was performed without anesthesia. The endometrial biopsy was extracted from the tube using cold saline solution. The saline solution was removed by centrifugation (1000 g , 5 min), and the remaining endometrial sample was snap-frozen in liquid nitrogen and stored at −80°C until further analysis.

Total RNA isolation

Total RNA was purified using the miRNeasy Mini Kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions.

Total RNA concentration and RNA purity were measured with a Lunatic spectrometer (Unchained labs, Pleasanton, CA, USA), while RNA integrity was evaluated using an Agilent 2100 Bioanalyzer (Agilent Technologies, Santa Clara, CA, USA).

Microarray analyses and bioinformatics

Microarray analysis was performed using Clariom D Array (Applied Biosystems, Waltham, MA, USA) for human samples. The total RNA was processed and labeled using the GeneChip Whole Transcript PLUS reagent kit according to manufactuer’s instructions (Applied Biosystems). Background correction, normalization, and gene expression index calculation of probe intensities were performed using the robust multi-array average method embedded in the Transcriptome Analysis Console (TAC) Software (version 4.0.3.14) (Thermo Fisher Scientific, WA, USA). Next, all probes, defined by TAC as being not expressed, were removed from further analysis.

All subsequent calculations were performed using the open source R-environment (R version 4.2.2) ( http://cran.r-project.org/ ).

First, the normalized probe expression matrix was collapsed by gene symbol using maximal probe intensity, thus providing one gene expression value per sample per gene and potential experiment batch-effects were removed using the ComBat function from the sra R-package. Based on the genes with top 500 most variable expression, the samples were clustered by principal component analysis (PCA) and visualized in a PCA-plot, and the associated gene expression levels were shown in a gene expression heatmap. The heatmap was created using the heatmap function embedded in the ComplexHeatmap R-package ( Gu et al ., 2016 ), while the principal components were calculated using prcomp function from the stats R-package and visualized in a three-dimensional PCA plot using the plot3d function from the rgl R-package.

Then, a differential gene expression analysis and a gene set enrichment analysis (GSEA) were performed. The differential gene expression analysis between seminal plasma and placebo-treated women was performed by using an unpaired limma t -test embedded in the limma R-package ( Ritchie et al ., 2015 ). All comparisons were adjusted for multiple testing using the false discovery rate (FDR), and genes with FDR ≤0.05 were considered as being significantly differentially expressed between the compared groups.

The GSEA was performed using the clusterProfiler R-package. GSEA was run on pre-ranked individual expressed genes using the Log2 fold change as ranking metric. The collection of human KEGG (Kyoto Encyclopedia of Genes and Genomes, http://www.genome.jp/kegg/ ), BIOCARTA, and Reactome ( https://reactome.org/ ) defined gene sets were used as input for the analysis. The GSEA was conducted using 1000 permutations, and minimum and maximum gene sets size were set to 15 and 500, respectively. Gene sets with FDR ≤0.05 were considered as being statistically significantly enriched.

To obtain an overview of the identified gene sets function, a manual search was performed to register how the pathways were classified and indexed in the selected databases. After this, a list of the most common categories was created and the pathways were manually attributed to the different categories.

For identification of intersections between the lists of up-regulated and down-regulated genes in our study and in the animals and in vitro studies ( Chen et al. , 2014 ; Schjenken et al. , 2015 ; Martinez et al. , 2019 ; Bogacki et al. , 2020 ), we used the get.venn.partitions function from the VennDiagram R-package. We also performed a manual comparison of our gene sets and the one listed in the compared studies.

Continuous variables were expressed as mean and 95% CI, and categorical variables as numbers (n).

A two-tailed un-paired Student’s t -test and the Chi-squared test were used to compare continuous variables and categorical variables, respectively. For all analyses, P  < 0.05 was considered statistically significant. STATA (StataCorp. 2019. Stata Statistical Software: Release 16. College Station, TX, USA: StataCorp LLC) was used for statistical analysis.

Study population

The participants’ recruitment started in 2020 until January 2023 with significant delays due to the COVID-19 pandemic. The planned study end date was March 2023, so the study was terminated even though the number of included participants did not reach the estimated sample size but for this reason, we decided to only perform analysis on the primary outcome.

In total, 30 women undergoing IVF treatments were invited to participate. Of them, 17 women declined to participate, and 1 woman wanted to participate, but the study was terminated before she could be included. Twelve women gave their written consent to participate. They were assessed for eligibility and then randomized into two groups. Seven women were allocated to receive a seminal plasma application, and five women were allocated to receive a placebo application. Two women in the seminal plasma group did not receive the seminal plasma application because they had an anovulatory cycle and did not participate again in the study. Due to a failed endometrial biopsy collection, one woman in the placebo group was excluded from the analysis. In summary, five women in the seminal plasma group and four in the placebo group were analyzed ( Fig. 2 ). No significant differences regarding age, BMI, smoking, drinking habits, and number of previous IVF attempts were observed between the two groups, as shown in Table 1 . Two women receiving seminal plasma had a live birth after the IVF treatment. All the other participants had a failed treatment without embryo transfer.

Flow diagram showing the enrollment of participants, treatment allocation, and analysis.

Patients’ characteristics.

Microarray analyses

The two transcriptomic analyses of endometrial samples showed that seminal plasma changed the endometrial gene expression profile.

The differential gene expression analysis showed a total of 565 genes, which were regulated by seminal plasma; 351 genes were upregulated by seminal plasma compared to placebo, and 241 genes were downregulated. However, after adjusting for multiple testing, there was no significantly differentially expressed genes (DEGs) between the two groups. The top 10 upregulated and the top 10 downregulated DEGs are listed in Table 2 . Among the listed top genes, some were related to extracellular matrix organization, cell growth, differentiation, and immune response. The complete list of DEGs is presented in Supplementary Table S1 .

Top 10 upregulated and downregulated differentially expressed genes between seminal plasma and placebo.

In the GSEA, all genes were ranked by the log2 fold change (seminal plasma versus placebo) and used as input to test if any gene sets or biological pathways were de-regulated between the two groups. Using the BIOCARTA, KEGG, and REACTOME databases, we identified 417 gene sets as significantly differentially enriched between the seminal plasma and the placebo group. Specifically, 18 pathways from BIOCARTA database, 85 pathways from the KEGG database, and 313 gene sets from REACTOME database were positively enriched. One gene set from REACTOME database was negatively enriched. The entire list of identified gene sets is presented in Supplementary Table S2 .

A substantial number of enriched gene sets were associated with metabolic processes, signal transduction, and the immune system but also, gene sets associated with cell viability, proliferation, and cellular movement were significantly enriched ( Fig. 3 ). Additionally, the analysis also found gene sets associated with disease processes, especially infectious diseases and cancer as being significantly enriched.

Differentially enriched pathways’ functional distribution.

A selection of relevant differentially enriched gene pathways is shown in Table 3 , including immunoregulatory gene pathways, cell proliferation, metabolism, and survival gene pathways. Gene pathways involved in implantation, embryo development, oocyte maturation, and angiogenesis are also present, such as the angiogenesis related VEGF signaling pathway, the embryonic development associated Hedgehog signaling pathway, and the oocyte maturation and meiosis signaling pathways.

Selection of relevant differentially enriched pathways in the three different databased used.

The comparison analysis between our study and studies performed in pigs, mice, and in vitro human endometrial cells ( Chen et al. , 2014 ; Schjenken et al. , 2015 ; Martinez et al. , 2019 ; Bogacki et al. , 2020 ) showed common gene pathways ( Table 4 ) and commonly expressed genes ( Supplementary Table S3 ) affected by seminal plasma.

List of comparable pathways between our study and animals and in vitro studies.

The arrows indicate the activation state in the compare studies and if the pathway was positively or negatively enriched in our study. For the study of Martinez et al. , it was not possible to collect information regarding the pathway regulation.

This study suggests that seminal plasma application around ovulation has a prolonged effect on the endometrial gene expression profile that might influence embryo implantation and pregnancy progression. To our knowledge, this is the first study in humans investigating endometrial transcriptional modifications induced by seminal plasma application. This study found pathways and gene sets showing an effect of seminal plasma on the endometrium.

It is known that after exposure to seminal plasma, there is an initial pro-inflammatory response in the endometrium with the recruitment of immune cells and the release of proinflammatory cytokines to remove microorganisms and superfluous sperm, and to initiate an adaptive immune response. Then during the implantation, there is a shift toward a more anti-inflammatory condition with the production of regulatory T cells (Treg), to promote tolerance toward the implanting embryo and promote its development ( Schjenken and Robertson, 2020 ; Ahmadi et al. , 2022 ). To our knowledge, this is one of the first studies in humans evaluating endometrial transcriptomic changes after seminal plasma application during the implantation window. Another study from 2012 assessed the effect of seminal fluid in the human ectocervix delivered by intercourse during the peri-ovulatory phase ( Sharkey et al. , 2012 ). In this study, seminal fluid exposure induced the production of proinflammatory cytokines and chemokines and the recruitment of macrophages, dendritic cells, and memory T cells. Moreover, it stimulated the expression of genes and gene pathways related to inflammation and immune response ( Sharkey et al. , 2012 ).

Similarly, in our study, 16% of the identified gene pathways were related to the immune system. All the pathways in our study were positively enriched except one. Some of the most relevant positively enriched pathways were related to the activation of T lymphocytes, both effector and Treg, like the CTLA4, Csk, and Tob signaling pathways, and immunoregulation.

Interestingly, the transforming growth factor (TGF) Beta signaling pathway, which plays an important role in Treg cell development and regulation, was positively enriched ( Li and Flavell, 2008 ). Pro-inflammatory response pathways, like the Natural killer cell-mediated cytotoxicity, the toll-like receptor, and Il12 signaling pathways, were also positively enriched. Indeed, a balance between pro- and anti-inflammatory responses is necessary to achieve implantation and successful pregnancy development ( Pantos et al. , 2022 ).

Other positively enriched pathways were related to proliferation, cell survival, cell–cell communication, and angiogenesis, like the MAPK family signaling cascades and VEGF signaling pathways, which promote endometrial receptivity and implantation ( Imajo et al. , 2006 ; Guo et al. , 2021 ). The signaling by WNT and TGF beta receptor in epithelial to mesenchymal transition, involved in the decidualization process, were also positively enriched ( Owusu-Akyaw et al. , 2019 ). Seminal plasma also stimulated oocyte maturation and embryo development. Indeed, pathways involved in embryo development, such as the Hedgehog signaling pathway, were positively enriched ( Briscoe and Thérond, 2013 ).

The only negatively enriched pathway in our study was the triglyceride metabolism pathway, which is coherent with the positive enrichment of the PPAR-alpha pathway, which reduces triglyceride levels and regulates energy homeostasis and inflammation ( Tyagi et al. , 2011 ).

Similar studies investigating the effect of seminal plasma on the endometrium have been performed in pigs, mice, and in vitro human endometrial cells ( Chen et al. , 2014 ; Schjenken et al. , 2015 ; Martinez et al. , 2019 ; Bogacki et al. , 2020 ). Two pig studies evaluated endometrial transcriptomic changes 6 days after intrauterine seminal plasma application ( Martinez et al. , 2019 ; Bogacki et al. , 2020 ). One study in mice examined endometrial transcriptomic changes 8 h after mating with seminal fluid-deficient mice ( Schjenken et al. , 2015 ). Finally, one in vitro study investigated seminal plasma’s effect on human endometrial epithelial cells and stromal fibroblasts ( Chen et al. , 2014 ).

Comparing our results with the above-mentioned studies, we found several common pathways affected by seminal plasma. Most of the pathways were related to the immune system, cell survival, and movement. We also compared the available list of genes in these studies with our results, and we discovered several genes present in both our study and the pig and mouse studies. The functions of these genes are related to the immune system, cell proliferation, and cell survival. No common genes were found when comparing our results with the in vitro human study ( Chen et al. , 2014 ). However, for the in vitro study, we could not find the complete list of genes but only a reduced list, which might be the reason why we did not find any commonly expressed genes between our studies.

Our results, in accordance with the above-mentioned studies, suggest the role of seminal plasma in modulating the maternal immune system and its involvement in ovulation, embryo development, and endometrial receptivity ( Chen et al. , 2014 ; Schjenken et al. , 2015 ; Martinez et al. , 2019 ; Bogacki et al. , 2020 ). Another in vitro study on human endometrial stromal and epithelial cells evaluating the effect of seminal plasma on decidualization showed that seminal plasma promoted decidualization through the action of seminal proteins, especially interleukin 11. Interestingly, similar to our study, this study also found that seminal plasma activated pathways related to cell survival, cell morphology, cellular development, cellular movement, and gene expression ( George et al. , 2020 ).

Seminal plasma might stimulate the endometrium through direct or indirect effects. Indeed, in humans, most of seminal plasma is delivered in the ectocervix after intercourse and only a small amount reaches the endometrium thought uterine peristaltic contractions or attached to the sperm surface ( Schjenken and Robertson, 2020 ). Studies in mice showed that seminal fluid activates and expands the population of Treg in the lymph nodes draining the uterus, which are then recruited into the uterus and contribute to the immune tolerance toward the implanting embryo ( Robertson et al. , 2009 ; Guerin et al. , 2011 ). In humans, a similar observation has been made. Indeed, seminal fluid exposure stimulates an immune response in the ectocervix and the recruitment of Treg and other immune cells in the lymph nodes draining the genital tract ( Sharkey et al. , 2012 ). A change in the pool of available immune cells could indirectly affect the endometrium, attenuating the repertoire of immune cells available for recruitment from peripheral blood to the uterus during the luteal phase.

The results of the current study were limited by the small number of included participants. Although 565 genes were found to be differentially regulated by seminal plasma, no significant difference was found after FDR correction. Maybe a larger study could have revealed specific genes of relevance. Moreover, it was not always possible to collect the endometrial samples after the exact same number of days from the seminal plasma application, due to practical limitations at the clinic. The samples were collected between Days 5 and 8 from the seminal plasma/placebo application, corresponding to the menstrual cycle’s mid-secretory phase. The secretory phase is characterized by elevated gene expression changes to prepare the endometrium for implantation ( Ruiz-Alonso et al. , 2012 ). For this reason, samples collected on Days 5 and 8 might express different gene sets.

The study was undertaken in women registered at the clinic without a male partner undergoing fertility treatments, whom we assumed had low chances of being exposed to seminal plasma during treatments. For this reason, the results cannot be generalized to the entire population of women undergoing ART. The comparison analysis with animals and in vitro studies also had some limitations. Indeed, the studies presented major differences in treatment, sample collection timing, seminal plasma location application, and species-specific physiology characteristics, which limited the chances of finding similarities with our results. For example, in the mouse study ( Schjenken et al. , 2015 ), the samples were collected only after 8 h from seminal plasma exposure. Moreover, pig and mouse reproductive anatomy differs from human anatomy since seminal fluid directly contacts the endometrium. The studies also used different microarray platforms and pathway analysis tools, decreasing the chances of finding comparable results.

One final consideration regarding our study design is that we only investigated the effect of seminal plasma on the endometrium without sperm. However, it is possible that also sperm affect the endometrial transcriptome, considering that in humans, it is mostly the sperm that have access to the higher reproductive tract. Studies in humans and animals showed that both sperm and seminal plasma have a role in stimulating the female reproductive tract and their combined exposure elicit the maximal effect ( Schjenken and Robertson, 2020 ).

In conclusion, finding similar endometrial transcriptomic modifications across species and in vitro human endometrial cells provide additional evidence that seminal plasma plays an active role in reproduction, which is highly conserved throughout evolution, and is not merely a transportation medium for spermatozoa. Even though ART success rates indicate that seminal plasma is not required for implantation and pregnancy development, studies in animals and humans showed it increases embryo quality and implantation ( Schjenken and Robertson, 2020 ; Ahmadi et al. , 2022 ). The clinical trials performed in humans have been promising, but the study populations have been too small to observe significant differences ( Crawford et al. , 2015 ; Ata et al. , 2018 ; Saccone et al. , 2019 ). Our study aligns with these studies and shows that also in humans, seminal plasma might be a valuable tool to increase the implantation rate. New randomized controlled studies should be performed to assess the beneficial effect of using seminal plasma during ART treatments. Its use might be particularly beneficial for donor sperm treatments of women with no male partner, where it might be assumed that the woman is not exposed to seminal plasma during the entire treatment period.

Supplementary data are available at Molecular Human Reproduction online.

The microarray results have been submitted to GEO with ID GSE241134. Other relevant data produced in this study will be shared upon request to the corresponding author.

The authors are grateful to the study nurse Karina Blach for all her help throughout the entire project. We also want to thank Professor Chunsen Wu for the statistical support provided and all the staff, doctors, nurses, lab technicians, and secretaries at the Fertility Clinic and genetics department of Odense University Hospital.

L.C made substantial contributions to the study design and the acquisition, analysis and interpretation of the data, and drafted the manuscript. M.B made substantial contributions in the analysis and interpretation of the data and revision of the manuscript. D.L.E. made substantial contribution to the development of laboratory procedures and revised the article. T.V.E. made substantial contribution to the study design and the revision of manuscript. M.T. made substantial contributions to the study design, interpretation of the data, and revision of the article. J.F. made substantial contributions to the study design, interpretation of the data, and revision of the manuscript. All authors approved the final manuscript.

A.P. Møller Fonden (project number 3177052), the Faculty of Health Sciences of Southern Denmark University, and the Region of Southern Denmark (project number 2171696).

D.L.E. holds shares of the European Sperm Bank. The other authors have nothing to declare.

Achache H , Revel A. Endometrial receptivity markers, the journey to successful embryo implantation . Hum Reprod Update 2006 ; 12 : 731 – 746 .

Google Scholar

Aflatoonian A , Ghandi S , Tabibnejad N. The effect of intercourse around embryo transfer on pregnancy rate in assisted reproductive technology cycles . Int J Fertil Steril 2009 ; 2 : 169 – 172 .

Ahmadi H , Csabai T , Gorgey E , Rashidiani S , Parhizkar F , Aghebati-Maleki L. Composition and effects of seminal plasma in the female reproductive tracts on implantation of human embryos . Biomed Pharmacother 2022 ; 151 : 113065 .

Ata B , Abou-Setta AM , Seyhan A , Buckett W. Application of seminal plasma to female genital tract prior to embryo transfer in assisted reproductive technology cycles (IVF, ICSI and frozen embryo transfer) . Cochrane Database Syst Rev 2018 ; 2 : Cd011809 .

Bellinge BS , Copeland CM , Thomas TD , Mazzucchelli RE , O’Neil G , Cohen MJ. The influence of patient insemination on the implantation rate in an in vitro fertilization and embryo transfer program . Fertil Steril 1986 ; 46 : 252 – 256 .

Bogacki M , Jalali BM , Wieckowska A , Kaczmarek MM. Prolonged effect of seminal plasma on global gene expression in porcine endometrium . Genes (Basel) 2020 ; 11 : 11 .

Briscoe J , Thérond PP. The mechanisms of Hedgehog signalling and its roles in development and disease . Nat Rev Mol Cell Biol 2013 ; 14 : 416 – 429 .

Chen JC , Johnson BA , Erikson DW , Piltonen TT , Barragan F , Chu S , Kohgadai N , Irwin JC , Greene WC , Giudice LC et al.  Seminal plasma induces global transcriptomic changes associated with cell migration, proliferation and viability in endometrial epithelial cells and stromal fibroblasts . Hum Reprod 2014 ; 29 : 1255 – 1270 .

Chicea R , Ispasoiu F , Focsa M. Seminal plasma insemination during ovum-pickup—a method to increase pregnancy rate in IVF/ICSI procedure. A pilot randomized trial . J Assist Reprod Genet 2013 ; 30 : 569 – 574 .

Comba C , Bastu E , Dural O , Yasa C , Keskin G , Ozsurmeli M , Buyru F , Serdaroglu H. Role of inflammatory mediators in patients with recurrent pregnancy loss . Fertil Steril 2015 ; 104 : 1467 – 1474.e1461 .

Crawford G , Ray A , Gudi A , Shah A , Homburg R. The role of seminal plasma for improved outcomes during in vitro fertilization treatment: review of the literature and meta-analysis . Hum Reprod Update 2015 ; 21 : 275 – 284 .

Danish Patient Safety Authority . Covid 19 guidelines.  https://en.stps.dk/covid-19 (April 2020, date last accessed).

Diedrich K , Fauser BC , Devroey P , Griesinger G ; Evian Annual Reproduction (EVAR) Workshop Group . The role of the endometrium and embryo in human implantation . Hum Reprod Update 2007 ; 13 : 365 – 377 .

European Centre for Disease Prevention and Control. Covid-19 guidelines. https://www.ecdc.europa.eu/en/covid-19 (April 2020, date last accessed).

Fatemi HM , Popovic-Todorovic B. Implantation in assisted reproduction: a look at endometrial receptivity . Reprod Biomed Online 2013 ; 27 : 530 – 538 .

Friedler S , Ben-Ami I , Gidoni Y , Strassburger D , Kasterstein E , Maslansky B , Komarovsy D , Bern O , Ron-El R , Raziel A. Effect of seminal plasma application to the vaginal vault in in vitro fertilization or intracytoplasmic sperm injection treatment cycles-a double-blind, placebo-controlled, randomized study . J Assist Reprod Genet 2013 ; 30 : 907 – 911 .

George AF , Jang KS , Nyegaard M , Neidleman J , Spitzer TL , Xie G , Chen JC , Herzig E , Laustsen A , Marques de Menezes EG et al.  Seminal plasma promotes decidualization of endometrial stromal fibroblasts in vitro from women with and without inflammatory disorders in a manner dependent on interleukin-11 signaling . Hum Reprod 2020 ; 35 : 617 – 640 .

Gu Z , , Eils R , , Schlesner M. Complex heatmaps reveal patterns and correlations in multidimensional genomic data . Bioinformatics 2016 ; 32 : 2847 – 2849 .

Guerin LR , Moldenhauer LM , Prins JR , Bromfield JJ , Hayball JD , Robertson SA. Seminal fluid regulates accumulation of FOXP3+ regulatory T cells in the preimplantation mouse uterus through expanding the FOXP3+ cell pool and CCL19-mediated recruitment . Biol Reprod 2011 ; 85 : 397 – 408 .

Guo X , Yi H , Li TC , Wang Y , Wang H , Chen X. Role of vascular endothelial growth factor (VEGF) in human embryo implantation: clinical implications . Biomolecules 2021 ; 11 : 11 .

Imajo M , Tsuchiya Y , Nishida E. Regulatory mechanisms and functions of MAP kinase signaling pathways . IUBMB Life 2006 ; 58 : 312 – 317 .

Johansson M , Bromfield JJ , Jasper MJ , Robertson SA. Semen activates the female immune response during early pregnancy in mice . Immunology 2004 ; 112 : 290 – 300 .

Li MO , Flavell RA. TGF-beta: a master of all T cell trades . Cell 2008 ; 134 : 392 – 404 .

Marquardt RM , Kim TH , Shin J-H , Jeong J-W. Progesterone and Estrogen Signaling in the Endometrium: What Goes Wrong in Endometriosis? . IJMS 2019 ; 20 : 3822 .

Martinez CA , Cambra JM , Parrilla I , Roca J , Ferreira-Dias G , Pallares FJ , Lucas X , Vazquez JM , Martinez EA , Gil MA et al.  Seminal plasma modifies the transcriptional pattern of the endometrium and advances embryo development in pigs . Front Vet Sci 2019 ; 6 : 465 .

Massimiani M , Lacconi V , La Civita F , Ticconi C , Rago R , Campagnolo L. Molecular Signaling Regulating Endometrium–Blastocyst Crosstalk . IJMS 2019 ; 21 : 23 .

Mayer RB , Ebner T , Yaman C , Hartl J , Sir A , Krain V , Oppelt P , Shebl O. Influence of intracervical and intravaginal seminal plasma on the endometrium in assisted reproduction: a double-blind, placebo-controlled, randomized study . Ultrasound Obstet Gynecol 2015 ; 45 : 132 – 138 .

O’Leary S , Jasper MJ , Robertson SA , Armstrong DT. Seminal plasma regulates ovarian progesterone production, leukocyte recruitment and follicular cell responses in the pig . Reproduction 2006 ; 132 : 147 – 158 .

O’Leary S , Jasper MJ , Warnes GM , Armstrong DT , Robertson SA. Seminal plasma regulates endometrial cytokine expression, leukocyte recruitment and embryo development in the pig . Reproduction 2004 ; 128 : 237 – 247 .

Owusu-Akyaw A , Krishnamoorthy K , Goldsmith LT , Morelli SS. The role of mesenchymal-epithelial transition in endometrial function . Hum Reprod Update 2019 ; 25 : 114 – 133 .

Pantos K , Grigoriadis S , Maziotis E , Pistola K , Xystra P , Pantou A , Kokkali G , Pappas A , Lambropoulou M , Sfakianoudis K et al.  The Role of Interleukins in Recurrent Implantation Failure: A Comprehensive Review of the Literature . IJMS 2022 ; 23 : 2198 .

Paria BC , Lim H , Das SK , Reese J , Dey SK. Molecular signaling in uterine receptivity for implantation . Semin Cell Dev Biol 2000 ; 11 : 67 – 76 .

Qasim SM , Trias A , Karacan M , Shelden R , Kemmann E. Does the absence or presence of seminal fluid matter in patients undergoing ovulation induction with intrauterine insemination? Hum Reprod 1996 ; 11 : 1008 – 1010 .

Ritchie ME , , Phipson B , , Wu DI , , Hu Y , , Law CW , , Shi WEI , , Smyth GK. limma powers differential expression analyses for RNA-sequencing and microarray studies . Nucleic Acids Res 2015 ; 43 : e47 .

Robertson SA. Seminal fluid signaling in the female reproductive tract: lessons from rodents and pigs . J Anim Sci 2007 ; 85 : E36 – 44 .

Robertson SA , Guerin LR , Bromfield JJ , Branson KM , Ahlström AC , Care AS. Seminal fluid drives expansion of the CD4+CD25+ T regulatory cell pool and induces tolerance to paternal alloantigens in mice . Biol Reprod 2009 ; 80 : 1036 – 1045 .

Robertson SA , Sharkey DJ. Seminal fluid and fertility in women . Fertil Steril 2016 ; 106 : 511 – 519 .

Ruiz-Alonso M , Blesa D , Simón C. The genomics of the human endometrium . Biochim Biophys Acta 2012 ; 1822 : 1931 – 1942 .

Saccone G , Di Spiezio Sardo A , Ciardulli A , Caissutti C , Spinelli M , Surbek D , von Wolff M. Effectiveness of seminal plasma in in vitro fertilisation treatment: a systematic review and meta-analysis . BJOG 2019 ; 126 : 220 – 225 .

Salleh N , Giribabu N. Leukemia inhibitory factor: roles in embryo implantation and in nonhormonal contraception . ScientificWorldJournal 2014 ; 2014 : 201514 .

Schjenken JE , Glynn DJ , Sharkey DJ , Robertson SA. TLR4 signaling is a major mediator of the female tract response to seminal fluid in mice . Biol Reprod 2015 ; 93 : 68 .

Schjenken JE , Robertson SA. The female response to seminal fluid . Physiol Rev 2020 ; 100 : 1077 – 1117 .

Sharkey DJ , Tremellen KP , Jasper MJ , Gemzell-Danielsson K , Robertson SA. Seminal fluid induces leukocyte recruitment and cytokine and chemokine mRNA expression in the human cervix after coitus . J Immunol 2012 ; 188 : 2445 – 2454 .

Tremellen KP , Valbuena D , Landeras J , Ballesteros A , Martinez J , Mendoza S , Norman RJ , Robertson SA , Simón C. The effect of intercourse on pregnancy rates during assisted human reproduction . Hum Reprod 2000 ; 15 : 2653 – 2658 .

Tyagi S , Gupta P , Saini AS , Kaushal C , Sharma S. The peroxisome proliferator-activated receptor: a family of nuclear receptors role in various diseases . J Adv Pharm Technol Res 2011 ; 2 : 236 – 240 .

von Wolff M , Rösner S , Germeyer A , Jauckus J , Griesinger G , Strowitzki T. Intrauterine instillation of diluted seminal plasma at oocyte pick-up does not increase the IVF pregnancy rate: a double-blind, placebo controlled, randomized study . Hum Reprod 2013 ; 28 : 3247 – 3252 .

von Wolff M , Rösner S , Thöne C , Pinheiro RM , Jauckus J , Bruckner T , Biolchi V , Alia A , Strowitzki T. Intravaginal and intracervical application of seminal plasma in in vitro fertilization or intracytoplasmic sperm injection treatment cycles—a double-blind, placebo-controlled, randomized pilot study . Fertil Steril 2009 ; 91 : 167 – 172 .

Email alerts

Citing articles via.

• Contact ESHRE
• Recommend to your Library

Affiliations

• Online ISSN 1460-2407
• Copyright © 2024 European Society of Human Reproduction and Embryology
• About Oxford Academic
• Publish journals with us
• University press partners
• What we publish
• New features  
• Open access
• Institutional account management
• Rights and permissions
• Get help with access
• Accessibility
• Advertising
• Media enquiries
• Oxford University Press
• Oxford Languages
• University of Oxford

Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide

• Copyright © 2024 Oxford University Press
• Cookie settings
• Cookie policy
• Privacy policy
• Legal notice

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

Tiny Tales from Africa: The Animals I (Gibbs)

• Last updated
• Save as PDF
• Page ID 127427

• Laura Gibbs
• University of Oklahoma

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

Welcome to Tiny Tales from Africa: The Animals (volume 1). This is a collection of two hundred stories from Africa featuring animal characters, and each story is just 100 words long. 

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• My Account Login
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• Matters Arising
• Open access
• Published: 27 May 2024

Animal magnetic sensitivity and magnetic displacement experiments

• Kenneth J. Lohmann   ORCID: orcid.org/0000-0003-1068-148X 1 ,
• Nathan F. Putman   ORCID: orcid.org/0000-0001-8485-7455 2 ,
• Sönke Johnsen 3 &
• Catherine M. F. Lohmann   ORCID: orcid.org/0000-0003-3767-0967 1  

Communications Biology volume  7 , Article number:  650 ( 2024 ) Cite this article

Metrics details

• Animal behaviour
• Animal migration

Matters Arising to this article was published on 27 May 2024

The Original Article was published on 20 February 2023

arising from W. T. Schneider et al. Communications Biology https://doi.org/10.1038/s42003-023-04530-w (2023)

Compelling evidence that animals use magnetic maps for navigation comes from magnetic displacement experiments in which animals are exposed to magnetic signatures (combinations of magnetic intensity, inclination, and occasionally, declination) that exist in different geographic regions 1 , 2 , 3 . Diverse species respond to magnetic displacements as if they have been geographically displaced. In a recent paper, Schneider et al. 4 argue that, if one assumes that sensitivity to variations in magnetic fields is low, then most magnetic signatures mark larger areas than researchers expect, and the same signatures might exist at multiple geographic locations. (Note that they use ‘sensitivity’ to mean the ability to discriminate between similar signals rather than the ability to detect a minimal signal). In their view, most magnetic signatures used previously are too ambiguous for animals to interpret. This opinion is puzzling, because, if true, then animals would presumably respond to these ‘ambiguous’ magnetic signatures with confusion and disorientation, rather than with directed movements that make sense in the context of their movement ecology, as is observed. This apparent contradiction can be resolved by recognizing that the sensitivity used by Schneider et al. 4 deviates significantly from estimates derived empirically. Here we discuss evidence from the literature that animals may be considerably more sensitive to magnetic field parameters than analyses by Schneider et al. 4 assume.

Schneider et al. 4 base their analyses on what they say is “the highest likely level of sensitivity to magnetic parameters in animals”. Without providing justification, they assume that animals can detect no less than 0.5 degrees of inclination and no less than 200 nT of intensity. In reality, magnetic sensitivity has not been established definitively in any animal, but numerous studies imply considerably higher sensitivity (Tables  1 and 2 ).

For example, the assumption that 0.5 degrees of inclination represents the highest sensitivity of animals conflicts with two recent studies on birds, both of which suggest exceptional sensitivity to this magnetic parameter (Table  1 ). In the first, Wynn et al. 5 demonstrate that small changes in inclination angle along a coastline are correlated with changes in nesting locations of shearwaters ( Puffinus puffinus ); of the 109 birds that changed location, the majority did so when the field changed by 0.02 degrees or less. In the second, Wynn et al. 6 present evidence that migratory reed warblers ( Acrocephalus scirpaceus ) use specific, presumably learned, inclination angle values to mark the endpoint of their return migrations. Because recovery sites of adult birds differed on average by about 5 km from the locations predicted by the inclination model, the results are consistent with an ability to detect inclination differences of at least 0.04–0.05 degrees. Similarly, an assumption of low magnetic sensitivity is difficult to reconcile with growing evidence that some animals, such as lobsters and newts, use magnetic maps over distances of only 4–37 km 7 , 8 .

The assumption that 200 nT represents the limits of intensity detection in animals is also contradicted by many studies (Table  2 ). In two species of salmon, for example, subtle changes in field intensity have been correlated with changes in the proportion of fish that take one of two migratory routes around Vancouver Island to arrive at the Fraser River 9 . For sockeye salmon ( Oncorhynchus nerka ), every ~31 nT increase is correlated with another 10% of the salmon shifting their migratory route north 9 . For pink salmon ( Oncorhynchus gorbuscha ), every ~22 nT increase is correlated with another 10% of salmon shifting their migratory route north 9 .

Accumulating evidence thus suggests that animal magnetic sensitivity is significantly higher, and possibly even a full order of magnitude better, than Schneider et al. 4 assume, both for inclination (Table  1 ) and for intensity (Table  2 ). This casts doubt on the validity of their analysis and, in particular, on their critiques of previously published papers, especially given that these new analyses do not change the interpretation of earlier studies 10 .

In effect, Schneider et al. 4 reimagine the world as it might appear to an animal with poor magnetic sensitivity and a global knowledge of geography, an approach that inverts what is known and unknown. We know from magnetic displacements how an animal responds to a specific magnetic field. We do not know the animal’s magnetic sensitivity or whether the animal is aware, as Schneider et al. 4 worry, that a similar field exists far away in a place it never goes. We do not know how large an area the signature represents to the animal (a localized area or a broad region), or whether the animal imagines itself to be anywhere at all. We do not know how sensitivity to magnetic fields is distributed within animal populations, i.e., whether population-level responses reflect the sensitivity of most individuals, or of just some particularly accurate individuals, or, instead, represent wisdom-of-the-crowd effects in which weakly sensitive individuals collectively appear to display higher sensitivity 11 . In the absence of such information, we favor a more conservative approach in which experiments reveal responses of animals, and data, rather than assumptions, shape discussion.

The emerging vision of magnetic maps is expansive, encompassing diverse strategies, the use of different magnetic parameters by different animals, and the recognition that natural selection is indifferent to whether a navigation system is perfect or fits human conceptions 1 . The precision of a map is much less important than its utility to the organism. Natural selection will favor even a rough map if it enhances survival. Indeed, some animal maps may consist entirely of simple rules that prevent animals from straying out of a favorable geographic range 1 , 2 , 3 .

In sum, there is general agreement that sensitivity is one factor that influences the specificity of an animal’s magnetic map 12 , 13 , 14 , but we find no basis for disparaging earlier work. Magnetic displacement is a robust technique for determining whether animals derive positional information from Earth’s magnetic field. We encourage our fellow researchers to eschew assumptions regarding sensitivity, focus on strong experimental design, and simply let the animals show us what they can do.

Lohmann, K. J., Goforth, K. M., Mackiewicz, A. G., Lim, D. S. & Lohmann, C. M. F. Magnetic maps in animal navigation. J. Comp. Physiol. A 208 , 41–67 (2022).

Article   Google Scholar  

Lohmann, K. J., Lohmann, C. M. F. & Putman, N. F. Magnetic maps in animals: nature’s GPS. J. Exp. Biol. 210 , 3697–3705 (2007).

Article   PubMed   Google Scholar  

Putman, N. F. Marine migrations. Curr. Biol. 28 , R972–R976 (2018).

Article   CAS   PubMed   Google Scholar  

Schneider, W. T., Packmor, F., Lindecke, O. & Holland, R. A. Sense of doubt: inaccurate and alternate locations of virtual magnetic displacements may give a distorted view of animal magnetoreception ability. Comm. Biol. 6 , 187 (2023).

Wynn, J., Padget, O., Mouritsen, H., Perrins, C. & Guilford, T. Natal imprinting to the Earth’s magnetic field in a pelagic seabird. Curr. Biol. 30 , 2869–2873.e2 (2020).

Wynn, J. et al. Magnetic stop signs signal a European songbird’s arrival at the breeding site after migration. Science 375 , 446–449 (2022).

Boles, L. C. & Lohmann, K. J. True navigation and magnetic maps in spiny lobsters. Nature 421 , 60–63 (2003).

Diego-Rasilla, F. J. & Phillips, J. B. Evidence for the use of a high-resolution magnetic map by a short-distance migrant, the Alpine newt ( Ichthyosaura alpestris ). J. Exp. Biol. 224 , jeb238345 (2021).

Putman, N. F., Jenkins, E. S., Michielsens, C. G. J. & Noakes, D. L. G. Geomagnetic imprinting predicts spatio-temporal variation in homing migration of pink and sockeye salmon. J. R. Soc. Interface 11 , 20140542–20140542 (2014).

Article   PubMed   PubMed Central   Google Scholar  

Lohmann, K. J., Putman, N. F., Johnsen, S. & Lohmann, C. M. F. Misconceptions about magnetic maps. Preprint at https://doi.org/10.5281/zenodo.10052196 (2023).

Brothers, J. R. & Lohmann, K. J. Evidence for geomagnetic imprinting and magnetic navigation in the natal homing of sea turtles. Curr. Biol. 25 , 392–396 (2015).

Gould, J. L. The map sense of pigeons. Nature 296 , 205–211 (1982).

Lohmann, K. J. & Lohmann, C. M. F. Detection of magnetic field intensity by sea turtles. Nature 380 , 59–61 (1996).

Article   CAS   Google Scholar  

Komolkin, A. V. et al. Theoretically possible spatial accuracy of geomagnetic maps used by migrating animals. J. R. Soc. Interface 14 , 20161002 (2017).

Rodda, G. H. The orientation and navigation of juvenile alligators: evidence of magnetic sensitivity. J. Comp. Physiol. A 154 , 649–658 (1984).

Keeton, W. T., Larkin, T. S. & Windsor, D. M. Normal fluctuations in the earth’s magnetic field influence pigeon orientation. J. Comp. Physiol. 95 , 95–103 (1974).

Dennis, T. E., Rayner, M. J. & Walker, M. M. Evidence that pigeons orient to geomagnetic intensity during homing. Proc. R. Soc. B: Biol. Sci. 274 , 1153–1158 (2007).

Southern, W. E. Gull orientation by magnetic cues: a hypothesis revisited. Ann. N. Y. Acad. Sci. 188 , 295–309 (1971).

Walker, M. M. & Bitterman, M. E. Honeybees can be trained to respond to very small changes in geomagnetic field intensity. J. Exp. Biol. 145 , 489–494 (1989).

Kirschvink, J. L. & Gould, J. L. Biogenic magnetite as a basis for magnetic field detection in animals. Biosystems 13 , 181–201 (1981).

Download references

Author information

Authors and affiliations.

Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA

Kenneth J. Lohmann & Catherine M. F. Lohmann

LGL Ecological Research Associates, Bryan, TX, USA

Nathan F. Putman

Department of Biology, Duke University, Durham, NC, USA

Sönke Johnsen

You can also search for this author in PubMed   Google Scholar

Contributions

K.J.L. and C.M.F.L. wrote the initial manuscript. S.J. and N.F.P. contributed to the development of the ideas and assisted with writing.

Corresponding author

Correspondence to Kenneth J. Lohmann .

Ethics declarations

Competing interests.

The authors declare no competing interests.

Peer review

Peer review information.

Communications Biology thanks John Phillips, and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Christina Karlsson Rosenthal.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/ .

Reprints and permissions

About this article

Cite this article.

Lohmann, K.J., Putman, N.F., Johnsen, S. et al. Animal magnetic sensitivity and magnetic displacement experiments. Commun Biol 7 , 650 (2024). https://doi.org/10.1038/s42003-024-06269-4

Download citation

Received : 28 May 2023

Accepted : 28 April 2024

Published : 27 May 2024

DOI : https://doi.org/10.1038/s42003-024-06269-4

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

By submitting a comment you agree to abide by our Terms and Community Guidelines . If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.