Anisogamy

Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a sperm cell, whereas the larger gamete is female, typically an egg cell. Anisogamy is predominant among multicellular organisms.^[1] In both plants and animals, gamete size difference is the fundamental difference between females and males.^[2]

Anisogamy most likely evolved from isogamy.^[3] Since the biological definition of male and female is based on gamete size, the evolution of anisogamy is viewed as the evolutionary origin of male and female sexes.^[4]^[5] Anisogamy is an outcome of both natural selection and sexual selection,^[6] and led the sexes to different primary and secondary sex characteristics^[7] including sex differences in behavior.^[8]

Geoff Parker, Robin Baker, and Vic Smith were the first to provide a mathematical model for the evolution of anisogamy that was consistent with modern evolutionary theory.^[4] Their theory was widely accepted but there are alternative hypotheses about the evolution of anisogamy.^[9]^[1]

^ ^a ^b Lehtonen, J.; Kokko, Hanna; Parker, Geoff A. (October 2016). "What do isogamous organisms teach us about sex and the two sexes?". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 371 (1706). doi:10.1098/rstb.2015.0532. PMC 5031617. PMID 27619696.
^ Davies, Nicholas B.; Krebs, John R. (2009-07-17). An Introduction to Behavioural Ecology. John Wiley & Sons. pp. 175–206. ISBN 978-1-4443-1402-1. Archived from the original on 2024-03-28. Retrieved 2021-06-15.
^ Cite error: The named reference Pitnick-2008 was invoked but never defined (see the help page).
^ ^a ^b Lehtonen, Jussi (2021-03-05). "The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness". Cells. 10 (3): 573. doi:10.3390/cells10030573. ISSN 2073-4409. PMC 7998237. PMID 33807911.
^ Togashi, Tatsuya; Bartelt, John L.; Yoshimura, Jin; Tainaka, Kei-ichi; Cox, Paul Alan (2012-08-21). "Evolutionary trajectories explain the diversified evolution of isogamy and anisogamy in marine green algae". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): 13692–13697. Bibcode:2012PNAS..10913692T. doi:10.1073/pnas.1203495109. ISSN 0027-8424. PMC 3427103. PMID 22869736.
^ Leonard, Janet; Cordoba-Aguilar, Alex (2010-07-19). The Evolution of Primary Sexual Characters in Animals. Oxford University Press, USA. pp. 18–20. ISBN 978-0-19-532555-3. Archived from the original on 2024-03-28. Retrieved 2021-08-19.
^ Encyclopedia of Animal Behavior. Vol. 2. Academic Press. 2019-01-21. p. 7. ISBN 978-0-12-813252-4. Archived from the original on 2024-03-28. Retrieved 2021-11-27.
^ Andersson, Malte (2019-12-31). Sexual Selection. Princeton University Press. ISBN 978-0-691-20727-8. Archived from the original on 2024-03-28. Retrieved 2021-11-27.
^ Majerus, M. E. N. (2003). Sex Wars: Genes, Bacteria, and Biased Sex Ratios. Princeton University Press. pp. 7–8. ISBN 978-0-691-00981-0. Archived from the original on 2024-03-28. Retrieved 2021-08-19.

[Lehtonen-2016-1] Lehtonen, J.; Kokko, Hanna; Parker, Geoff A. (October 2016). "What do isogamous organisms teach us about sex and the two sexes?". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 371 (1706). doi:10.1098/rstb.2015.0532. PMC 5031617. PMID 27619696.

[2] Davies, Nicholas B.; Krebs, John R. (2009-07-17). An Introduction to Behavioural Ecology. John Wiley & Sons. pp. 175–206. ISBN 978-1-4443-1402-1. Archived from the original on 2024-03-28. Retrieved 2021-06-15.

[Pitnick-2008-3] Cite error: The named reference Pitnick-2008 was invoked but never defined (see the help page).

[Lehtonen-2021-4] Lehtonen, Jussi (2021-03-05). "The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness". Cells. 10 (3): 573. doi:10.3390/cells10030573. ISSN 2073-4409. PMC 7998237. PMID 33807911.

[5] Togashi, Tatsuya; Bartelt, John L.; Yoshimura, Jin; Tainaka, Kei-ichi; Cox, Paul Alan (2012-08-21). "Evolutionary trajectories explain the diversified evolution of isogamy and anisogamy in marine green algae". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): 13692–13697. Bibcode:2012PNAS..10913692T. doi:10.1073/pnas.1203495109. ISSN 0027-8424. PMC 3427103. PMID 22869736.

[6] Leonard, Janet; Cordoba-Aguilar, Alex (2010-07-19). The Evolution of Primary Sexual Characters in Animals. Oxford University Press, USA. pp. 18–20. ISBN 978-0-19-532555-3. Archived from the original on 2024-03-28. Retrieved 2021-08-19.

[7] Encyclopedia of Animal Behavior. Vol. 2. Academic Press. 2019-01-21. p. 7. ISBN 978-0-12-813252-4. Archived from the original on 2024-03-28. Retrieved 2021-11-27.

[8] Andersson, Malte (2019-12-31). Sexual Selection. Princeton University Press. ISBN 978-0-691-20727-8. Archived from the original on 2024-03-28. Retrieved 2021-11-27.

[9] Majerus, M. E. N. (2003). Sex Wars: Genes, Bacteria, and Biased Sex Ratios. Princeton University Press. pp. 7–8. ISBN 978-0-691-00981-0. Archived from the original on 2024-03-28. Retrieved 2021-08-19.

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