Oogamy

Oogamy in animals: small, motile sperm on the surface of an ovum

Oogamy is a form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete (also known as ovum) is immotile, while the small male gamete (also known as spermatozoon) is mobile.^[1] Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous.

Oogamy is found in most sexually reproducing species, including all vertebrates, land plants, and some algae. The ancestral state of sexual reproduction is believed to be isogamy, with oogamy evolving through anisogamy. Once oogamy evolves, males and females typically differ in various aspects. Internal fertilization may have originated from oogamy, although some studies suggest ^[2]: 37 that oogamy in certain species may have evolved before the transition from external to internal fertilization. In streptophytes, oogamy occurred before the split from green algae.

Occurrence

Oogamy is found in almost all animal species that reproduce sexually.^[3][4] There are exceptions, such as the opiliones that have immobile sperm.^[5]

Oogamy is found in all land plants,^[6] and in some red algae, brown algae and green algae.^[7]: 309 Oogamy is favored in land plants because only one gamete has to travel through harsh environments outside the plant.^[7]: 376 Oogamy is also present in oomycetes.^[8]

Etymology

The term oogamy was first used in the year 1888.^[9] It derives from the Greek noun "oon" (ΩΟΝ = egg) and the Greek verb "gameo" (ΓΑΜΕΩ -> ΓΑΜΩ = to have sex/to reproduce) and eventually means "reproduction through eggs".

Evolution

Main article: Evolution of sexual reproduction

It is generally accepted that isogamy is the ancestral state^[10] and that oogamy evolves from isogamy through anisogamy.^{[11][4]: 309 [12]} When oogamy has evolved, males and females typically differ in many aspects. Oogamy evolved before the transition from external to internal fertilization.^{[2]: 37 [4]: 326}

In streptophytes, oogamy occurred before the split from green algae.^[13]

See also

• Gamete
• Anisogamy
• Isogamy

References

1. Fusco, Giuseppe; Minelli, Alessandro (2019-10-10). The Biology of Reproduction. Cambridge University Press. pp. 111–112. ISBN 978-1-108-49985-9. Retrieved 29 March 2021.
2. Nozaki, H; Yamada, TK; Takahashi, F; Matsuzaki, R; Nakada, T (2014). "New "missing link" genus of the colonial volvocine green algae gives insights into the evolution of oogamy". BMC Evolutionary Biology. 14 (1): 37. Bibcode:2014BMCEE..14...37N. doi:10.1186/1471-2148-14-37. PMC 4015742. PMID 24589311.
3. Bell, Graham (2019-11-28). The Masterpiece of Nature: The Evolution and Genetics of Sexuality. Routledge. p. 63. ISBN 978-1-000-49744-1.
4. Dusenbery, David B. (2009). Living at Micro Scale: The Unexpected Physics of Being Small. Harvard University Press. p. 32. ISBN 978-0-674-06021-0.
5. Leonard, Janet; Cordoba-Aguilar, Alex (2010-07-19). The Evolution of Primary Sexual Characters in Animals. Oxford University Press, USA. pp. 18–19. ISBN 978-0-19-532555-3.
6. Simpson, Michael G. (2010-07-19). Plant Systematics. Academic Press. p. 58. ISBN 978-0-08-092208-9.
7. Raven, Peter H.; Evert, University Ray F.; Evert, Ray F.; Eichhorn, Susan E.; Eichhorn, University Susan E. (2005). Biology of Plants. W. H. Freeman. ISBN 978-0-7167-1007-3.
8. Buaya, Anthony T.; Thines, Marco (2020). "An overview on the biology and phylogeny of the early-diverging oomycetes". Philippine Journal of Systematic Biology. 14 (1): 1-20. doi:10.26757/pjsb2020a14004.
9. "Definition of OOGAMY". Merriam-Webster. Retrieved 2021-09-14.
10. Pitnick, Scott S.; Hosken, Dave J.; Birkhead, Tim R. (2008-11-21). Sperm Biology: An Evolutionary Perspective. Academic Press. pp. 43–44. ISBN 978-0-08-091987-4.
11. Kumar, Awasthi & Ashok. Textbook of Algae. Vikas Publishing House. p. 363. ISBN 978-93-259-9022-7.
12. Hörandl, Elvira; Hadacek, Franz (August 2020). "Oxygen, life forms, and the evolution of sexes in multicellular eukaryotes". Heredity. 125 (1): 1–14. doi:10.1038/s41437-020-0317-9. ISSN 1365-2540. PMC 7413252. PMID 32415185.
13. Geng, Sa; De Hoff, Peter; Umen, James G. (2014-07-08). "Evolution of Sexes from an Ancestral Mating-Type Specification Pathway". PLOS Biology. 12 (7): e1001904. doi:10.1371/journal.pbio.1001904. ISSN 1544-9173. PMC 4086717. PMID 25003332.