Copulation (zoology)

In zoology, copulation is animal sexual behavior in which a male introduces sperm into the female's body, especially directly into her reproductive tract.[1][2] This is an aspect of mating. Many animals that live in water use external fertilization, whereas internal fertilization may have developed from a need to maintain gametes in a liquid medium in the Late Ordovician epoch. Internal fertilization with many vertebrates (such as reptiles, some fish, and most birds) occur via cloacal copulation, known as cloacal kiss (see also hemipenis), while mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization.[3][4]

In non-primate mammals (rodents, canines, felines, bovines, and equines), the anatomy of the reproductive organs and some circuits of the nervous system are specifically organized for heterosexual copulation.[5] On the other hand, human sexual intercourse stems from a change in biological factors that controls the copulation of mammals, and is mainly learned.[6]

In spiders and insects

Spiders are often confused with insects, but they are not insects; instead, they are arachnids.[7][8] Spiders have separate male and female sexes. Before mating and copulation, the male spider spins a small web and ejaculates on to it. He then stores the sperm in reservoirs on his large pedipalps, from which he transfers sperm to the female's genitals. The females can store sperm indefinitely.[9]

For primitive insects, the male deposits spermatozoa on the substrate, sometimes stored within a special structure; courtship involves inducing the female to take up the sperm package into her genital opening, but there is no actual copulation.[10][11] In groups that have reproduction similar to spiders, such as dragonflies, males extrude sperm into secondary copulatory structures removed from their genital opening, which are then used to inseminate the female. In dragonflies, it is a set of modified sternites on the second abdominal segment.[12] In advanced groups of insects, the male uses its aedeagus, a structure formed from the terminal segments of the abdomen, to deposit sperm directly (though sometimes in a capsule called a spermatophore) into the female's reproductive tract.[13]

In mammals

Non-primate mammals

Some scientific studies show that the general neuroanatomic organization of non-primate mammals is specifically designed for heterosexual copulation.[14] By simplifying, there are three major hardwired neurobiological circuits, controlled by hormones: A) The olfactory circuits (red arrows, diagram below), which underlie sexual arousal and sexual orientation; B) The circuits of sexual reflexes (lordosis, erection, ejaculation ... orange arrows), which allow copulation; C) The circuits of sexual rewards (reward system associated with penis / clitoris - blue arrows), which are involved in sexual learning (especially sexual motivation).[15]

Simplified diagram of the neurobiological circuits that control reproductive behavior in non-primate female mammals. By simplifying, the hormones control the activity of these innate circuits. They activate the secretion of pheromones and their detection,[16] and disinhibit the lordosis reflex.[17] The pheromones of the male (1) are detected and treated by the olfactory circuits (2 - red arrows). They trigger sexual arousal in the female, stimulate hippocampal neurogenesis,[18] and, via the hypothalamus, facilitate the lordosis reflex.[19] The mount by the male stimulates the rump of the female (3) which triggers the lordosis reflex (4 - orange arrows).[17] The arching of the back induces the presentation of the vagina to the male (5). Then the clitoral sensations during penetration (6) trigger ovulation in some species (and in all ancestral species[20]); activate the reward system (7 - blue arrows), inducing the learning of sexual motivations[21] and to stay close to the copulation partner (attachment).[22]

Particularly in the female, copulation is controlled by several innate neurobiological processes, including the motor sexual reflex of lordosis[17] (see diagram below).

Simplified diagram of the neurobiological circuits of the lordosis reflex, specific to female mammals, and indispensable to the realization of copulation. This complex motor sexual reflex is hardwired in the spinal cord and receives modulatory afferents from the forebrain.[17][15][23] Caption: a) Median preoptic nucleus; b) Anterior hypothalamic nucleus; c) Ventromedial hypothalamic nucleus; d) Midbrain reticular formation; e) Vestibulo-spinal tract; f) Reticulo-spinal tract; g) Dorsal roots L1, L2, L5, L6 and S1. NB: The neural circuit is bilateral. The diagram is simplified for greater clarity.

By simplifying, the female can not have any other sexual activity than lordosis.

In the male, the realization of copulation is more complex, because some learning is necessary. Nevertheless, the innate processes (retrocontrol of penis intromission in the vagina, rhythmic movement of the pelvis, detection of female pheromones ...) are specific to copulation. These innate processes direct learning to heterosexual copulation.[24]

Thus, through the coordination of hormones, pheromones and sexual reflexes, there is a true reproductive behavior in non-primate mammals.

Evolution of copulation control in hominids

Evolution of the main neurobiological factors that control the sexual behavior of mammals.[15]

In the case of mammals with a highly developed brain (chimpanzee, bonobo, Orangutans, and dolphins), the cerebral structure has evolved. As a result of these evolved differences, the human intercourse depends on another type of neurobiological control:[6]

  • Female lordosis behaviour became secondary in hominidae and is apparently non-functional in humans.[25] Sexual stimuli no longer trigger immobilization or reflex arching of the back. If a woman gets onto all fours, curves her back and remains still, it is no longer a reflex movement triggered by sexual stimuli, but a voluntary movement.[15]
  • Pheromones become secondary. 90% of sex pheromone receptor genes become pseudogens,[26] and the vomeronasal organ is altered.[27]
  • The sexual activities are gradually dissociated from the hormonal cycles,[25] especially in pan paniscus[28] and humans.
  • Sexual learning, induced by sexual rewards and the reward system, become a major factor in hominids.[14][29]
  • The major development of the cortex in hominids leads to the gradual emergence of complex cognitive abilities, which have enabled the human species to develop culture.[30]

Thus, the functional dynamics of the copulation behavior has been modified in hominids: the reproductive behavior becomes an erotic behavior.[6] Vaginal coitus is still practiced in humans, but it is no longer a reflex motor activity, guided by pheromones and controlled by hormones. It is rather an erotic activity, among others, carried out voluntarily to obtain cerebral reward (sexual pleasure [29]).[15]

Further reading

  • Peter J Chenoweth; Steven Lorton (30 April 2014). Animal Andrology: Theories and Applications. CABI. ISBN 978-1-78064-316-8.
  • Møller, A. P., and T. R. Birkhead. "Copulation behaviour in mammals: evidence that sperm competition is widespread." Biological Journal of the Linnean Society 38.2 (1989): 119-131.
  • Birkhead, Timothy R., L. Atkin, and A. P. Møller. "Copulation behaviour of birds." Behaviour 101.1 (1987): 101-138.
  • Anders Agmo Functional and dysfunctional sexual behavior Elsevier 2007
  • (in French) Wunsch S. (2014) To understand the origins of human sexuality. Neurosciences, ethology, anthropology. Comprendre les origines de la sexualité humaine. Neurosciences, éthologie, anthropologie. L'Esprit du Temps.
  • Richard Sadleir (2 December 2012). The Reproduction of Vertebrates. Elsevier Science. ISBN 978-0-323-15935-7.
  • Broom, D.M.; Fraser, A.F. Domestic Animal Behaviou... CABI. pp. 155–. ISBN 978-1-78064-053-2.
  • P. Bateson (29 June 2013). Perspectives in Ethology. Springer Science & Business Media. pp. 12–. ISBN 978-1-4615-7572-6.
  • Roger L. Gentry (14 July 2014). Behavior and Ecology of the Northern Fur Seal. Princeton University Press. pp. 172–. ISBN 978-1-4008-6472-0.
  • Richard Estes (1991). The Behavior Guide to African Mammals: Including Hoofed Mammals, Carnivores, Primates. University of California Press. ISBN 978-0-520-08085-0.
  • Carlson, Debra A. Reproductive biology of the coyote (Canis latrans): integration of behavior and physiology. Utah State University, 2008.
  • Castro, Ana Mafalda Lopes Sardica Velez. Mexican gray wolf courtship and mating: behavior & basic endocrinology during breeding season. Diss. Universidade de Lisboa. Faculdade de Medicina Veterinária, 2016.
  • Szykman, Micaela, et al. "Courtship and mating in free-living spotted hyenas." Behaviour 144.7 (2007): 815-846.
  • Dixson, Alan F. "Baculum length and copulatory behavior in primates." American Journal of Primatology 13.1 (1987): 51-60.

References

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  2. "Copulation". Dorland's Medical Dictionary for Health Consumers, 2007/TheFreeDictionary.com for various dictionary definitions. Retrieved September 6, 2012.
  3. Cecie Starr; Christine Evers; Lisa Starr (2010). Cengage Advantage Books: Biology: A Human Emphasis. Cengage Learning. pp. 630–631. ISBN 1133170056. Retrieved December 9, 2010.
  4. Edward J. Denecke Jr. (2006). New York State Grade 8 Intermediate Level Science Test. Barron's Educational Series. p. 105. ISBN 0764134337. Retrieved December 9, 2014.
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  11. Franz Engelmann (2013). The Physiology of Insect Reproduction: International Series of Monographs in Pure and Applied Biology: Zoology. Elsevier. pp. 58–59. ISBN 1483186539. Retrieved December 9, 2014.
  12. Janet Leonard; Alex Cordoba-Aguilar (2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. p. 334. ISBN 0199717036. Retrieved December 9, 2014.
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  16. Lin H.H., Cao D.S., Sethi S., Zeng Z., Chin J.S., Chakraborty T.S., Shepherd A.K., Nguyen C.A., Yew J.Y., Su C.Y., Wang J.W. Hormonal modulation of pheromone detection enhances male courtship success. Neuron, 90(6):1272-1285, 2016
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