Sperm competition
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Sperm competition is "competition between sperm of two or more males for the fertilization of an ova" (Parker 1970). Sperm competition is often compared to having tickets in a raffle; a male has a better chance of winning (i.e. fathering offspring) the more tickets he has (i.e. the more sperm he inseminates a female with). However, sperm are costly to produce (Olsson et al, 1997; Wedell et al, 2002) and the energy may be spent elsewhere such as defending a territory to the exclusion of other males; the distribution of resources are called strategies. The optimum amount is the evolutionarily stable strategy (ESS).
Sperm competition may lead to evolutionary adaptations for producing more sperm, such as larger testes. Such adaptations cost and so species with low sperm competition invest in mate competition instead. Other means of sperm competition could include improving the sperm itself or its packaging materials (spermatophore).
In primates Harcourt et al (1981) studied the relative size of testes compared to body mass against the mating system. They found that promiscuous chimpanzees have larger testes compared to polygynous gorillas.
The British biologist Geoffrey Parker proposed the concept of sperm competition in a 1970 paper.
See also
References
- Baker, Robin 1996. Sperm Wars: The Science of Sex ISBN 0788160044.
- Harcourt, A.H., Harvey, P.H., Larson, S.G., and Short, R.V. 1981. Testis weight, body weight and breeding system in primates, Nature 293: 55-57.
- Olsson, M., Madsen, T. & Shine, R. 1997. Is sperm really so cheap? Costs of reproduction in male adders, Vipera berus. Proceedings of the Royal Society of London B 264: 455-459.
- Parker, Geoffrey A. 1970. Sperm competition and its evolutionary consequences in the insects, Biological Reviews 45: 525-567.
- Shackelford, T. K. & Pound, N. 2005. Sperm Competition in Humans : Classic and Contemporary Readings ISBN 0387280367.
- Simmons, Leigh W. 2001. Sperm competition and its evolutionary consequences in the insects. Princeton University Press, ISBN 0-691-05988-8 and ISBN 0-691-05987-X
- Snook, Rhonda R. Postcopulatory reproductive strategies. Encyclopedia of Life Sciences http://www.els.net
- Wedell, N., Gage, M.J.G, & Parker, G. A. 2002. Sperm competition, male prudence and sperm-limited females. Trends in Ecology & Evolution, 7: 313-320.de:Spermienkonkurrenz