Simultaneous hermaphroditism explained

Simultaneous hermaphroditism is one of the two types of hermaphroditism, the other type being sequential hermaphroditism. In this form of hermaphroditism an individual has sex organs of both sexes and can produce both gamete types^[1] even in the same breeding season.^[2]

The distinction between simultaneous hermaphroditism and sequential hermaphroditism is not always clear.^[3] But unlike sequential hermaphrodites, simultaneous hermaphrodites are both male and female at sexual maturity. Also sex determination does not apply to simultaneous hermaphrodites (except in species with mix mating systems).^[4] In simultaneous hermaphrodites, self-fertilization is possible in some species, where in others it is absent.

Evolution

The evolution of anisogamy possibly contributed to the evolution of Simultaneous hermaphroditism.^[5] It is known that simultaneous hermaphroditism that exclusively reproduces through self-fertilization has evolved many times in plants and animals, but it might not last long evolutionarily.^[6]

The primary model explaining the evolution of simultaneous hermaphroditism from gonochorism in animals is the low density model.^[7] This model explains simultaneous hermaphroditism as a reproductive adaptation to limited mating opportunities. This is advantageous to simultaneous hermaphrodites that can self-fertilize, because they are able to reproduce even if they fail to find a sexual partner. The low density model is helpful for understanding the development of simultaneous hermaphroditism in many animal species. For example, in crustaceans simultaneous hermaphroditism can be found in groups that are sessile or live in environments with limited mating opportunities.^[8]

Plants

Most plants are simultaneous hermaphrodites^[9] with it occurring in 80% of angiosperms.

Animals

Simultaneous hermaphroditism is one of the most common sexual systems in animals.^[10] The majority of Cocculinoidea are simultaneous hermaphrodites^[11] and it occurs in over 67% of coral species.^[12]

Notes and References

1. Book: Cabej, Nelson R.. Building the Most Complex Structure on Earth: An Epigenetic Narrative of Development and Evolution of Animals. 2013-04-01. Newnes. 978-0-12-401729-0. 101. en.
2. Book: Charnov, Eric L. . The Theory of Sex Allocation. (MPB-18), Volume 18 . 2020-03-31 . Princeton University Press . 978-0-691-21005-6 . 7 . en.
3. Book: Ponder. Winston Frank. Biology and Evolution of the Mollusca, Volume 1. Lindberg. David R.. Ponder. Juliet Mary. 2019-11-18. CRC Press. 978-1-351-11565-0. 439. en.
4. Book: Fusco. Giuseppe. The Biology of Reproduction. Minelli. Alessandro. 2019-10-10. Cambridge University Press. 978-1-108-49985-9. 299–300. en.
5. Schärer L . February 2017 . The varied ways of being male and female . Molecular Reproduction and Development . 84 . 2 . 94–104 . 10.1002/mrd.22775 . 28032683 . free.
6. Book: Transitions Between Sexual Systems: Understanding the Mechanisms of, and Pathways Between, Dioecy, Hermaphroditism and Other Sexual Systems . Leonard JL . 2019-05-21 . Springer . 978-3-319-94139-4 . en.
7. Ghiselin . Michael . 1969 . The evolution of hermaphroditism among animals . The Quarterly Review of Biology . 44 . 2 . 189–208 . 10.1086/406066 . 4901396 . 38139187 . JSTOR.
8. Book: Beukeboom . Leo . The Evolution of Sex Determination . Perrin . Nicolas . 2014-06-12 . OUP Oxford . 978-0-19-163139-9 . 29–30 . en.
9. Book: Doust. Jon Lovett. Plant Reproductive Ecology: Patterns and Strategies. Doust. Lesley Lovett. 1988. Oxford University Press. 978-0-19-506394-3. 142. en.
10. Book: The Evolution of Primary Sexual Characters in Animals. Leonard J, Cordoba-Aguilar A. 2010-07-19. Oxford University Press, USA. 978-0-19-532555-3. 20. en.
11. Book: Leonard . Janet . The Evolution of Primary Sexual Characters in Animals . Cordoba-Aguilar . Alex . 2010-07-16 . Oxford University Press . 978-0-19-971703-3 . 130 . en.
12. Book: Avise, John C. . Hermaphroditism: A Primer on the Biology, Ecology, and Evolution of Dual Sexuality . 2011-03-18 . Columbia University Press . 978-0-231-52715-6 . 83 . en.