Gonochorism

In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female.[1] The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.[2]: 212–222 

Not to be confused with sexual dimorphism.

Gonochorism contrasts with simultaneous hermaphroditism but it may be hard to tell if a species is gonochoric or sequentially hermaphroditic. (e.g. Parrotfish, Patella ferruginea).[3] However, in gonochoric species individuals remain either male or female throughout their lives.[4] Species that reproduce by thelytokous parthenogenesis and do not have males can still be classified as gonochoric.[5]

Terminology
Look up gonochorism, gonochory, or unisexualism in Wiktionary, the free dictionary.

The term is derived from Greek (gone, generation) + (chorizein, to separate).[6] The term gonochorism originally came from German gonochorismus.[7]

Gonochorism is also referred to as unisexualism or gonochory.

Evolution
Main article: Evolution of sexual reproduction
For evolution of dioecy in plants, see Dioecy § Evolution of dioecy.

Gonochorism has evolved independently multiple times[8] and is very evolutionarily stable in animals.[9] Its stability and advantages have received little attention.[10]: 46  Its origin owes to the evolution of anisogamy,[11] but it is unclear if the evolution of anisogamy first led to hermaphroditism or gonochorism.[2]: 213 

Gonochorism is thought to be ancestral in polychaetes,[9]: 126  hexacorallia,[12]: 74  nematodes,[13]: 62  and hermaphroditic fishes. Gonochorism is thought to be ancestral in hermaphroditic fishes because it is widespread in basal clades of fish and other vertebrate lineages.[14]

Two papers from 2008 have suggested that transitions between hermaphroditism and gonochorism or vice versa have occurred in certain animal taxonomy groups between 10 and 20 times.[15] In a 2017 study involving 165 taxon groups, more evolutionary transitions from gonochorism to hermaphroditism were found than the reverse.[16]

Use across species

Animals

The term is most often used with animals, in which the species are usually gonochoric.

Gonochorism has been estimated to occur in 95% of animal species.[17] It is very common in vertebrate species, 99% of which are gonochoric.[18][19] 98% of fishes are gonochoric.[20] Mammals (including humans[21][22]) and birds are solely gonochoric.[23]

Tardigrades are almost always gonochoric.[24] 75% of snails are gonochoric.[25]

Most arthropods are gonochoric.[26] For example a majority of crustaceans are gonochoric.[27]

In animals, sex is most often genetically determined, but may be determined by other mechanisms. For example, alligators use temperature-dependent sex determination during egg incubation.

Plants

Plants which have single-sex individuals are typically called dioecious (vascular plants) or dioicous (bryophytes) instead of gonochoric. In flowering plants, individual flowers may be hermaphroditic (i.e. with both stamens and ovaries) or dioecious (unisexual), having either no stamens (i.e. no male parts) or no ovaries (i.e. no female parts). Among flowering plants with unisexual flowers, some also produce hermaphrodite flowers, and the three types may occur in different arrangements on the same or separate plants. Plant species can thus be hermaphrodite, monoecious, dioecious, trioecious, polygamomonoecious, polygamodioecious, andromonoecious, or gynomonoecious.

Unlike most flatworms, schistosomes are gonochoric. The narrow female can be seen emerging from the thicker male's gynecophoral canal below his ventral sucker.

Examples of species with gonochoric or dioecious pollination include hollies and kiwifruit. In these plants the male plant that supplies the pollen is referred to as the pollenizer.

Other reproductive strategies

Gonochorism stands in contrast to other reproductive strategies such as asexual reproduction and hermaphroditism. Closely related taxa can have differing sexual strategies – for example, the genus Ophryotrocha contains species that are gonochoric and species that are hermaphrodites.[28]

The sex of an individual may also change during its lifetime – this sequential hermaphroditism can, for example, be found in parrotfish[29][30] and cockles.

See also

References
  1. King RC, Stansfield WD, Mulligan PK (2006-07-27). "Gonochorism". A Dictionary of Genetics. Oxford University Press. p. 187. ISBN 978-0-19-976957-5.
  2. Kliman RM (2016). "Hermaphrodites". In Schärer L, Ramm S (eds.). Encyclopedia of Evolutionary Biology. Vol. 2. Academic Press. ISBN 978-0-12-800426-5. Archived from the original on 2019-10-20.
  3. Holub AM, Shackelford TK (2020). "Gonochorism". In Vonk J, Shackelford TK (eds.). Encyclopedia of Animal Cognition and Behavior (PDF). Cham: Springer International Publishing. pp. 1–3. doi:10.1007/978-3-319-47829-6_305-1. ISBN 978-3-319-47829-6. S2CID 240938739.
  4. West S (2009-09-28). Sex Allocation. Princeton University Press. p. 1. ISBN 978-1-4008-3201-9.
  5. Fusco G, Minelli A (2019-10-10). The Biology of Reproduction. Cambridge University Press. pp. 116–117. ISBN 978-1-108-49985-9.
  6. Winn, Philip (2003-09-02). Dictionary of Biological Psychology. Routledge. p. 698. ISBN 978-1-134-77815-7.
  7. "Definition of GONOCHORISM". www.merriam-webster.com. Retrieved 2021-09-29.
  8. Bachtrog, Doris; Mank, Judith E.; Peichel, Catherine L.; Kirkpatrick, Mark; Otto, Sarah P.; Ashman, Tia-Lynn; Hahn, Matthew W.; Kitano, Jun; Mayrose, Itay; Ming, Ray; Perrin, Nicolas (2014-07-01). "Sex Determination: Why So Many Ways of Doing It?". PLOS Biology. 12 (7): e1001899. doi:10.1371/journal.pbio.1001899. ISSN 1544-9173. PMC 4077654. PMID 24983465.
  9. Leonard, Janet L. (2013-10-01). "Williams' Paradox and the Role of Phenotypic Plasticity in Sexual Systems". Integrative and Comparative Biology. 53 (4): 671–688. doi:10.1093/icb/ict088. ISSN 1540-7063. PMID 23970358.
  10. Leonard JL (2019-05-21). Transitions Between Sexual Systems: Understanding the Mechanisms of, and Pathways Between, Dioecy, Hermaphroditism and Other Sexual Systems. Springer. ISBN 978-3-319-94139-4.
  11. Barnes, R. S. K.; Hughes, R. N. (1999-06-02). An Introduction to Marine Ecology. John Wiley & Sons. p. 202. ISBN 978-0-86542-834-8.
  12. Dubinsky, Zvy; Stambler, Noga (2010-12-02). Coral Reefs: An Ecosystem in Transition. Springer Science & Business Media. ISBN 978-94-007-0114-4.
  13. Schmidt-Rhaesa, Andreas (2013-12-18). Nematoda. Walter de Gruyter. ISBN 978-3-11-027425-7.
  14. Erisman BE, Petersen CW, Hastings PA, Warner RR (October 2013). "Phylogenetic perspectives on the evolution of functional hermaphroditism in teleost fishes". Integrative and Comparative Biology. 53 (4): 736–54. doi:10.1093/icb/ict077. PMID 23817661.
  15. Weeks, Stephen C. (18 June 2012). "The Role of Androdioecy and Gynodioecy in Mediating Evolutionary Transitions Between Dioecy and Hermaphroditism in the Animalia". Evolution. 66 (12): 3670–3686. doi:10.1111/j.1558-5646.2012.01714.x. PMID 23206127. S2CID 3198554.
  16. Sasson DA, Ryan JF (December 2017). "A reconstruction of sexual modes throughout animal evolution". BMC Evolutionary Biology. 17 (1): 242. doi:10.1186/s12862-017-1071-3. PMC 5717846. PMID 29207942.
  17. Muyle A, Bachtrog D, Marais GA, Turner JM (June 2021). "Epigenetics drive the evolution of sex chromosomes in animals and plants". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 376 (1826): 20200124. doi:10.1098/rstb.2020.0124. PMC 8059572. PMID 33866802.
  18. Skinner M (2018-06-29). "Evolution of Sex Determining Genes in Fish". In Pan Q, Guiguen Y, Herpin A (eds.). Encyclopedia of Reproduction. Academic Press. p. 168. ISBN 978-0-12-815145-7.
  19. Kuwamura T, Sunobe T, Sakai Y, Kadota T, Sawada K (2020-07-01). "Hermaphroditism in fishes: an annotated list of species, phylogeny, and mating system". Ichthyological Research. 67 (3): 341–360. doi:10.1007/s10228-020-00754-6. ISSN 1616-3915.
  20. Pandian, T. J. (2011-09-02). Sex Determination in Fish. CRC Press. p. 8. ISBN 978-1-4398-7919-1.
  21. Pierce BA (2012). Genetics: A Conceptual Approach. Macmillan. p. 75. ISBN 978-1-4292-3252-4.
  22. Muehlenbein MP (2010-07-29). Jones J (ed.). Human Evolutionary Biology. Cambridge University Press. p. 74. ISBN 978-0-521-87948-4.
  23. Kobayashi K, Kitano T, Iwao Y, Kondo M (June 2018). Reproductive and Developmental Strategies: The Continuity of Life. Springer. p. 290. ISBN 978-4-431-56609-0.
  24. Thorp, James H.; Covich, Alan P. (2010). Ecology and Classification of North American Freshwater Invertebrates. Academic Press. p. 468. ISBN 978-0-12-374855-3.
  25. Encyclopedia of Evolutionary Biology. Vol. 4. Academic Press. 2016-04-14. p. 50. ISBN 978-0-12-800426-5.
  26. Giribet, Gonzalo; Edgecombe, Gregory D. (2020-03-03). The Invertebrate Tree of Life. Princeton University Press. p. 249. ISBN 978-0-691-19706-7.
  27. Subramoniam, Thanumalaya (2016-09-27). Sexual Biology and Reproduction in Crustaceans. Academic Press. pp. 57–58. ISBN 978-0-12-809606-2.
  28. Prevedelli D, N'Siala GM, Simonini R (January 2006). "Gonochorism vs. hermaphroditism: relationship between life history and fitness in three species of Ophryotrocha (Polychaeta: Dorvilleidae) with different forms of sexuality". The Journal of Animal Ecology. 75 (1): 203–12. doi:10.1111/j.1365-2656.2006.01040.x. PMID 16903057.
  29. Bester C. "Stoplight parrotfish". Florida Museum of Natural History, Ichthyology Department. Archived from the original on 6 December 2009. Retrieved 15 December 2009.
  30. Afonso P, Morato T, Santos RS (2008). "Spatial patterns in reproductive traits of the temperate parrotfish Sparisoma cretense". Fisheries Research. 90 (1–3): 92–99. doi:10.1016/j.fishres.2007.09.029.
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