Pseudo-penis

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A pseudo-penis is any structure found on an animal that, while superficially appearing to be a penis, is derived from a different developmental path.

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Mammals

Male and female reproductive systems of the spotted hyena Anatomischer Anzeiger (1922) (18006271698).jpg
Male and female reproductive systems of the spotted hyena

In mammals, all intact developmentally typical males have a penis, but the clitoris in the females of the following species is sufficiently enlarged that it is usually termed a pseudo-penis: spotted hyena, [1] [2] juvenile fossa, [3] binturong, [4] lemur [5] and spider monkey. The fossa's enlarged clitoris is supported by an os clitoridis, a bone similar to the male's os penis. [3] The juvenile female fossa's os clitoridis and pseudo-penis shrink as she grows, unlike that of other pseudo-penis species. [3]

The mammalian pseudo-penis appears to be simply for display, though the spotted hyena is an exception: the female spotted hyena urinates, copulates, and gives birth through her pseudo-penis. This prevents males from mating without the full co-operation of females, which means that mating preferences of the female are predominant. [6]

Spotted hyena - Addo Elephant National Park (33948058355).jpg
Female spotted hyenas urinate through a pseudo-penis. [7]

Spotted hyenas are a matriarchal society, where adult females dominate adult males [8] and are also more aggressive than males. When a male hyena leaves his natal clan, he behaves submissively to all newly encountered hyenas; as a result, when he settles down with a new clan as a breeding male, he is submissive to all natal clan members. [9] It was hypothesized that the male hyena erected his penis to show submissiveness. [10] During greetings, hyenas would stand parallel to each other and sniff or lick the erect penis or anal scent gland. [10]

Mating hyenas.jpg
The male spotted hyena inserts his penis into the female's pseudo-penis during copulation. [7]

The spotted hyena's pseudo-penis has severe reproductive costs. Nearly all of her first-born cubs are stillborn, as the placenta is not long enough for the extended penile birth canal. In addition, the first birthing process is time-consuming, as it requires the meatus of the pseudo-penis to tear, allowing the fetus to pass through; as a result, the first-born often die of hypoxia. [11]

The female spider monkey has a clitoris that is called a pseudo-penis because it is especially developed and has a shallow perineal groove that retains and distributes urine droplets as she moves around. [12] The clitoris of female Geoffroy's spider monkeys is large and protrudes, looking like a penis. [13] This organ, called a pendulous clitoris because of the way it dangles externally, is actually larger than the male flaccid penis. [14] As a result, females are sometimes mistaken for males by human observers. [13] The enlarged clitoris is believed to aid males in determining sexual receptiveness, allowing them to touch the clitoris and smell their fingers to pick up chemical or olfactory cues to the female's reproductive status. [14]

Birds

Only 3% of avian species have a phallus. The most common genitalia among birds is the cloaca; a direct tract for elimination and reproduction in both of the sexes.[ citation needed ] Certain bird species, such as the ratites, screamers, waterfowl, and cracids (a family of arboreal galliformes) exhibit a phallus in males. A notable example of a bird with a pseudo-penis is the red-billed buffalo weaver, which do not use their pseudo-penis for direct insertion during copulation; however it does play a part in successful mating and stimulation. [15] Similarly to the red-billed buffalo weaver, the cassowary, a ratite, exhibits a pseudo-penis in both males and females. The male's pseudo-phallus is used to "invaginate", or to push the female's pseudo-phallus inside-out, and then ejaculates from the cloaca to ensure a successful mating.[ failed verification ]

Insects

The only known example of a pseudo-penis to occur in the insects is found in the barklouse genus Neotrogla . In this genus, the pseudo-penis plays a part in their rarely-seen sexual reversal. In this case, the male has a vagina-like structure while the female has a pseudo-penis. Some may be confused, wondering why the individuals with a vagina-like structure are considered male while the ones with the pseudo-penis are considered female. [16] This is because even though they have visible outer structures of the opposite sex, their inner structures are consistent to their sex. More important, the males produce sperm and the females produce eggs.

Females have a penis-like structure, called the gynosome that has a tube leading into their body to where their genitalia are located. [17] Neotrogla males have a structure resembling that of a vagina. However, on the inside of their body, they have male genitalia. When the female inserts her organ into the male, the tip of the pseudo penis inflates. When this tip inflates, species specific ridges and spines flare up that match up with the walls of the male's genital chamber. This serves two functions, to stimulate the male's reproductive organs, and to keep the male and female locked together. After they have been locked together, the only way to get the two to part would be to rip off the abdomen of the male. During the lengthy, 40- to 70-hour copulation process, these male genitalia structures ejaculate inside of the male's body. [18] The sperm is then deposited into the female's structure and then travels through a spermathecal duct to where it can fertilize the eggs.

Possible role of androstenedione

Androstenedione is a hormone that is converted to testosterone by enzymatic activity. [19] It is theorized that the dominance and morphological phenotype of a pseudo-penis observed in female hyenas is due to the presence of prenatal and postnatal androstenedione levels. Prenatal androgen levels dictate genitalia differences between male and female. Higher levels of androgen are observed in the second half of gestation which is theorized to cause masculinization in terms of dominance and aggression in hyenas. [20] Large amounts of androstenedione are produced in hyena ovarian tissues with little aromatase activity allowing the placenta to convert androstenedione to testosterone. [21] High concentrations of androgens is theorized to virilize the female hyena genitalia and kill ovarian follicles. [21] Postnatal androgen levels dictate growth in genitalia during puberty. Postnatal androgen levels are higher in females than males when they are younger; especially in infancy. [22] These high levels of androstenedione contribute to aggression and dominance and the masculinization of genitalia during puberty. [22]

See also

Related Research Articles

<span class="mw-page-title-main">Clitoris</span> Erectile female sexual organ

In amniotes, the clitoris is a female sex organ. In humans, it is the vulva's most erogenous area and generally the primary anatomical source of female sexual pleasure. The clitoris is a complex structure, and its size and sensitivity can vary. The visible portion, the glans, of the clitoris is typically roughly the size and shape of a pea and is estimated to have at least 8,000 nerve endings.

The glans is a vascular structure located at the tip of the penis in male mammals or a homologous genital structure of the clitoris in female mammals.

<span class="mw-page-title-main">Spotted hyena</span> Species of hyena

The spotted hyena, also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus Crocuta, native to sub-Saharan Africa. It is listed as being of least concern by the IUCN due to its widespread range and large numbers estimated between 27,000 and 47,000 individuals. The species is, however, experiencing declines outside of protected areas due to habitat loss and poaching. Populations of Crocuta, usually considered a subspecies of Crocuta crocuta, known as cave hyenas, roamed across Eurasia for at least one million years until the end of the Late Pleistocene. The spotted hyena is the largest extant member of the Hyaenidae, and is further physically distinguished from other species by its vaguely bear-like build, rounded ears, less prominent mane, spotted pelt, more dual-purposed dentition, fewer nipples, and pseudo-penis. It is the only placental mammalian species where females have a pseudo-penis and lack an external vaginal opening.

<span class="mw-page-title-main">Virilization</span> Biological development of male sex characteristics

Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens.

<span class="mw-page-title-main">Baculum</span> Bone in the penis

The baculum, also known as the penis bone, penile bone, os penis, os genitale, or os priapi, is a bone in the penis of many placental mammals. It is present in the penises of some primates, such as the gorilla and the chimpanzee. The baculum arises from primordial cells in soft tissues of the penis, and its formation is largely influenced by androgens. The bone lies above the urethra, and it aids sexual reproduction by maintaining stiffness during sexual penetration. The homologue to the baculum in female mammals is the baubellum, a bone in the clitoris.

<span class="mw-page-title-main">Clitoromegaly</span> Unusually large clitoris

Clitoromegaly is an abnormal enlargement of the clitoris that is mostly congenital; it is otherwise acquired through deliberately induced clitoral enlargement e.g. body modification by use of anabolic steroids, including testosterone. It can happen as part of a gender transition. It is not the same as normal enlargement of the clitoris seen during sexual arousal.

<span class="mw-page-title-main">Male reproductive system</span> Reproductive system of the human male

The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body, and within the pelvis.

<span class="mw-page-title-main">Human reproductive system</span> Organs involved in reproduction

The human reproductive system includes the male reproductive system, which functions to produce and deposit sperm, and the female reproductive system, which functions to produce egg cells and to protect and nourish the fetus until birth. Humans have a high level of sexual differentiation. In addition to differences in nearly every reproductive organ, there are numerous differences in typical secondary sex characteristics.

Sexual mimicry occurs when one sex mimics the opposite sex in its behavior, appearance, or chemical signalling.

<span class="mw-page-title-main">Sexual differentiation in humans</span> Process of development of sex differences in humans

Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. Sexual differentiation includes development of different genitalia and the internal genital tracts and body hair plays a role in sex identification.

Pseudohermaphroditism is an outdated term for when an individual's gonads were mismatched with their internal reproductive system and/or external genitalia. The term was contrasted with "true hermaphroditism", a condition describing an individual with both female and male reproductive gonadal tissues. Associated conditions includes Persistent Müllerian duct syndrome and forms of androgen insensitivity syndrome.

<span class="mw-page-title-main">Urinary meatus</span> Orifice of the urethra

The urinary meatus, also known as the external urethral orifice, is the opening of the urethra where urine exits the penis or vulva during urination. It is where semen exits the penis during ejaculation. The meatus has varying degrees of sensitivity to touch.

<span class="mw-page-title-main">Penis</span> Primary sexual organ of male animals

A penis is a male sex organ that is used to inseminate female or hermaphrodite animals during copulation. Such organs occur in both vertebrates and invertebrates, but not in all male animals.

The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.

An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs externally, although there are exceptions. For many species in the animal kingdom, the male intromittent organ is a hallmark characteristic of internal fertilization.

<span class="mw-page-title-main">Penile spines</span> Pointed structures on the penile glans and/or shaft

Many mammalian species have developed keratinized penile spines along the glans and/or shaft, which may be involved in sexual selection. These spines have been described as being simple, single-pointed structures (macaques) or complex with two or three points per spine (strepsirrhines). Penile spine morphology may be related to mating system.

<span class="mw-page-title-main">Prader scale</span> Rating system for the degree of virilization of human genitalia

The Prader scale or Prader staging, named after Andrea Prader, is a coarse rating system for the measurement of the degree of virilization of the genitalia of the human body and is similar to the Quigley scale. It primarily relates to virilization of the female genitalia in cases of congenital adrenal hyperplasia (CAH) and identifies five distinct stages, but in recent times has been used to describe the range of differentiation of genitalia, with normal infant presentation being shown on either end of the scale, female on the left (0) and male on the right (6).

The Phall-O-meter is a satirical measure that critiques medical standards for normal male and female phalluses. The tool was developed by Kiira Triea based on a concept by Suzanne Kessler and is used to demonstrate concerns with the medical treatment of intersex bodies.

The clitoris is a female sex organ present in mammals, ostriches and other amniotes.

References

  1. ↑ Place, Ned J.; Glickman, Stephen E. (2004). "Masculinization of Female Mammals: Lessons from Nature". Hypospadias and Genital Development. Advances in Experimental Medicine and Biology. Vol. 545. pp. 243–253. CiteSeerX   10.1.1.501.721 . doi:10.1007/978-1-4419-8995-6_15. ISBN   978-1-4613-4752-1. PMID   15086031.
  2. ↑ ADW: Crocuta crocuta: Information
  3. 1 2 3 Goodman S (2009). "Family Eupleridae (Madagascar Carnivores)". In Wilson D; Mittermeier R (eds.). Handbook of the Mammals of the World. Volume 1: Carnivores. Barcelona: Lynx Edicions. ISBN   978-84-96553-49-1. Archived from the original on 2011-07-25. Retrieved 2010-05-21.
  4. ↑ Archived May 16, 2006, at the Wayback Machine
  5. ↑ Angier 1999 , pp.  68–69 ; Hall 2005 , p.  344 ; Goodman 2009 .
  6. ↑ Owen, James (15 August 2007). "Hyenas Encourage Sex With Strangers to Prevent Incest". National Geographic News. Archived from the original on 8 February 2008.
  7. 1 2 Szykman, M.; Van Horn, R. C.; Engh, A.L.; Boydston, E. E.; Holekamp, K. E. (2007). "Courtship and mating in free-living spotted hyenas" (PDF). Behaviour. 144 (7): 815–846. CiteSeerX   10.1.1.630.5755 . doi:10.1163/156853907781476418. Archived from the original (PDF) on 30 November 2012. Retrieved 24 December 2011.
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  9. ↑ Holekamp, Kay E.; Dantzer, Ben; Stricker, Gregory; Shaw Yoshida, Kathryn C.; Benson-Amram, Sarah (May 2015). "Brains, brawn and sociality: a hyaena's tale". Animal Behaviour. 103: 237–248. doi:10.1016/j.anbehav.2015.01.023. PMC   4493912 . PMID   26160980.
  10. 1 2 East, MarionL.; Hofer, Heribert; Wickler, Wolfgang (December 1993). "The erect 'penis' is a flag of submission in a female-dominated society: greetings in Serengeti spotted hyenas". Behavioral Ecology and Sociobiology. 33 (6): 355–370. doi:10.1007/BF00170251. JSTOR   4600895. S2CID   23727803.
  11. ↑ Glickman, Stephen E.; Cunha, Gerald R.; Drea, Christine M.; Conley, Alan J.; Place, Ned J. (November 2006). "Mammalian sexual differentiation: lessons from the spotted hyena". Trends in Endocrinology & Metabolism. 17 (9): 349–356. doi:10.1016/j.tem.2006.09.005. PMID   17010637. S2CID   18227659.
  12. ↑ Dixson, Alan F. (2012). Primate Sexuality: Comparative Studies of the Prosimians, Monkeys, Apes, and Humans. Oxford University Press. p. 364. ISBN   978-0-19-954464-6 . Retrieved 2012-11-22.
  13. 1 2 Wainwright, M. (2002). The Natural History of Costa Rican Mammals. Zona Tropical. pp. 146–149. ISBN   0-9705678-1-2.
  14. 1 2 Campbell, C. & Gibson, K. (2008). "Spider monkey reproduction and sexual behavior". In Campbell, C. (ed.). Spider Monkeys. Cambridge University Press. pp. 266–283. ISBN   978-0-521-86750-4.
  15. ↑ Winterbottom, M.; Burke, T.; Birkhead, T. R. (May 1999). "A stimulatory phalloid organ in a weaver bird". Nature. 399 (6731): 28. Bibcode:1999Natur.399...28W. doi: 10.1038/19884 . S2CID   4431318.
  16. ↑ Ed Yong (April 17, 2014). "In This Insect, Females Have Penises And Males Have Vaginas". Not Exactly Rocket Science. National Geographic. Archived from the original on April 20, 2014.
  17. ↑ Yoshizawa, Kazunori; Ferreira, Rodrigo L.; Kamimura, Yoshitaka; Lienhard, Charles (May 2014). "Female Penis, Male Vagina, and Their Correlated Evolution in a Cave Insect". Current Biology. 24 (9): 1006–1010. doi: 10.1016/j.cub.2014.03.022 . hdl: 2115/56857 . PMID   24746797.
  18. ↑ Jason G. Goldman (April 17, 2014). "Scientists Discover the Gynosome, a New Kind of Sexual Organ". Gizmodo.
  19. ↑ Skinner, J. D.; Chimimba, Christian T. (2005-11-15). The Mammals of the Southern African Sub-region. Cambridge University Press. ISBN   9781107394056.
  20. ↑ French, Jeffrey A.; Mustoe, Aaryn C.; Cavanaugh, Jon; Birnie, Andrew K. (5 December 2013). "The influence of androgenic steroid hormones on female aggression in 'atypical' mammals". Philosophical Transactions of the Royal Society B: Biological Sciences. 368 (1631): 20130084. doi:10.1098/rstb.2013.0084. PMC   3826213 . PMID   24167314.
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  22. 1 2 Glickman, S E; Frank, L G; Davidson, J M; Smith, E R; Siiteri, P K (May 1987). "Androstenedione may organize or activate sex-reversed traits in female spotted hyenas". Proceedings of the National Academy of Sciences of the United States of America. 84 (10): 3444–3447. Bibcode:1987PNAS...84.3444G. doi: 10.1073/pnas.84.10.3444 . PMC   304887 . PMID   3472215.
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