Intersex (biology)

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Intersex is a general term for an organism that has sex characteristics that are between male and female. [1] It typically applies to a minority of members of gonochoric animal species such as mammals (as opposed to hermaphroditic species in which the majority of members can have both male and female sex characteristics). [2] Such organisms are usually sterile. [3]

Contents

Intersexuality can occur due to both genetic and environmental factors [4] and has been reported in mammals, fishes, nematodes, and crustaceans.

Mammals

Intersex can occur in mammals such as pigs, with it being estimated that 0.1% to 1.4% of pigs are intersex. [5] In Vanuatu, Narave pigs are sacred intersex pigs that are found on Malo Island. An analysis of Narave pig mitochondrial DNA by Lum et al. (2006) found that they are descended from Southeast Asian pigs. [6] [7] [8]

At least six different mole species have an intersex adaption where by the female mole has an ovotestis, "a hybrid organ made up of both ovarian and testicular tissue. This effectively makes them intersex, giving them an extra dose of testosterone to make them just as muscular and aggressive as male moles". The ovarian part of the ovotestis is reproductively functional. [9] [10]

Intersexuality in humans is relatively rare. Depending on the definition, the prevalence of intersex among humans has been reported to range around a figure of 0.018%. [11] [12]

Nematodes

Intersex is known to occur in all main groups of nematodes. Most of them are functionally female. Male intersexes with female characteristics have been reported but are less common. [13]

Fishes

Gonadal intersex occurs in fishes, where the individual has both ovarian and testicular tissue. Although it is a rare anomaly among gonochoric fishes, it is a transitional state in fishes that are protandric or protogynous. [14] Intersexuality has been reported in 23 fish families. [15]

Crustaceans

The oldest evidence for intersexuality in crustaceans comes from fossils dating back 70 million years ago. [4] Intersex has been reported in gonochoric crustaceans as early as 1729. A large amount of literature exists on intersexuality for isopoda and amphipoda, with there being reports of both intersex males and intersex females. [16]

See also

Related Research Articles

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<span class="mw-page-title-main">Sex-determination system</span> Biological system that determines the development of an organisms sex

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.

<span class="mw-page-title-main">Gonad</span> Gland that produces sex cells

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

Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.

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A hermaphrodite is an organism that possesses both male and female reproductive organs during its life.

Pseudohermaphroditism is an outdated term for when an individuals gonads was 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.

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An ovotestis is a gonad with both testicular and ovarian aspects. In humans, ovotestes are an infrequent anatomical variation associated with gonadal dysgenesis. The only mammals where ovotestes are not symptomatic of a disorder are moles, wherein females possess ovotestes along with a masculinized clitoris. These ovotestes in nonpregnant female moles secrete eight times as much testosterone as the ovotestes of pregnant moles. In invertebrates that are normally hermaphroditic, such as most gastropods in the clade Eupulmonata, an ovotestis is a common feature of the reproductive anatomy.

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References

  1. ↑ "intersex | Definition & Facts". Encyclopædia Britannica. Retrieved 2021-07-10. Intersex, in biology, an organism having physical characteristics intermediate between a true male and a true female of its species.
  2. ↑ Farrell A (2011-06-01). Encyclopedia of Fish Physiology: From Genome to Environment. Academic Press. ISBN   978-0-08-092323-9. Thus, strictly speaking, all hermaphrodites are intersex at one time point, but not all intersexes are hermaphrodites. This definition is usually applied to gonochoristic species to describe those individuals that are not normal for the species.
  3. ↑ "Malformation – Sexual anomalies". Encyclopedia Britannica. Encyclopædia Britannica, Inc. Retrieved 19 July 2021.
  4. 1 2 Ford, Alex T. (February 2012). "Intersexuality in Crustacea: an environmental issue?". Aquatic Toxicology (Amsterdam, Netherlands). 108: 125–129. doi:10.1016/j.aquatox.2011.08.016. ISSN   1879-1514. PMID   22265612.
  5. ↑ Hunter, R. H. F.; Hunter, Ronald Henry Fraser (1995-03-09). Sex Determination, Differentiation and Intersexuality in Placental Mammals. Cambridge University Press. p. 157. ISBN   978-0-521-46218-1.
  6. ↑ Lum, J. Koji; McIntyre, James K.; Greger, Douglas L.; Huffman, Kirk W.; Vilar, Miguel G. (November 14, 2006). "Recent Southeast Asian domestication and Lapita dispersal of sacred male pseudohermaphroditic "tuskers" and hairless pigs of Vanuatu". Proceedings of the National Academy of Sciences. 103 (46): 17190–17195. doi: 10.1073/pnas.0608220103 . PMC   1859908 . PMID   17088556.
  7. ↑ "Intersex Pigs". Southwest Pacific Research Project. Retrieved 2023-03-07.
  8. ↑ "Pigs in Paradise". Penn State University. Retrieved 2023-03-07.
  9. ↑ https://www.cbc.ca/radio/quirks/oct-17-coronavirus-and-pain-sampling-an-asteroid-intersex-moles-and-more-1.5763905/female-moles-are-intersex-they-have-testicle-like-tissue-that-helps-them-grow-big-and-tough-1.5763925,CBC Radio, accessed 2023-04-13
  10. ↑ M. Real, Francisca; Haas, Stefan A.; Franchini, Paolo; Xiong, Peiwen; Simakov, Oleg; Kuhl, Heiner; Schöpflin, Robert; Heller, David; Moeinzadeh, M-Hossein; Heinrich, Verena; Krannich, Thomas; Bressin, Annkatrin; Hartmann, Michaela F.; Wudy, Stefan A.; Dechmann, Dina K. N. (2020). "The mole genome reveals regulatory rearrangements associated with adaptive intersexuality". Science. 370 (6513): 208–214. doi:10.1126/science.aaz2582. PMC   8243244 . PMID   33033216.
  11. ↑ Leonard Sax (1 August 2002). "How common is intersex? a response to Anne Fausto-Sterling". Journal of Sex Research . 39 (3): 174–178. doi:10.1080/00224490209552139. ISSN   0022-4499. PMID   12476264. Wikidata   Q34163911.
  12. ↑ Selma Feldman Witchel (2018). "Disorders of Sex Development". Best Practice & Research. Clinical Obstetrics & Gynaecology. 48: 90–102. doi:10.1016/j.bpobgyn.2017.11.005. ISSN   1521-6934. PMC   5866176 . PMID   29503125. The estimated frequency of genital ambiguity is reported to be in the range of 1:2000-1:4500
  13. ↑ El-Bawab, Fatma (2020-01-18). Invertebrate Embryology and Reproduction. Academic Press. p. 431. ISBN   978-0-12-814115-1.
  14. ↑ Norris, David O.; Lopez, Kristin H. (2010-11-25). Hormones and Reproduction of Vertebrates. Academic Press. pp. 249–251. ISBN   978-0-08-095809-5.
  15. ↑ Pandian, T. J. (2010-09-15). Sexuality in Fishes. CRC Press. p. 38. ISBN   978-1-4398-4669-8.
  16. ↑ Cothran, Rickey; Thiel, Martin (2020-04-24). The Natural History of the Crustacea: Reproductive Biology: Volume VI. Oxford University Press. pp. 395–396. ISBN   978-0-19-068855-4.
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