Sperm competition: Difference between revisions
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The goal of evolution for all organisms is reproduction to ensure their genes are inherited by the next generation. From the male’s perspective, they face many struggles when attempting this. Males transfer sperm to the female that are inexpensive to produce. This means that males have the capacity of producing large numbers of sperm and can fertilize a large number of eggs as well. |
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In certain situations males might have limited access to females and those females may also be promiscuous, then the result is competition with other males. This competition will not only be for access to those females but also to fertilise the eggs of the females they mate with. This concept is referred to as is Sperm Competition. |
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'''Sperm competition''' is "[[competition (biology)|competition]] between [[sperm]] of two or more [[males]] for the [[fertilization]] of an [[ovum]]" (Parker 1970). Sperm competition is often compared to having [[ticket]]s 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). Male fruit flies have been shown to release 250% more sperm when another male is present, compared to being alone with the female (Gage 1991). |
'''Sperm competition''' is "[[competition (biology)|competition]] between [[sperm]] of two or more [[males]] for the [[fertilization]] of an [[ovum]]" (Parker 1970). Sperm competition is often compared to having [[ticket]]s 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). Male fruit flies have been shown to release 250% more sperm when another male is present, compared to being alone with the female (Gage 1991). |
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== References == |
== References == |
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*Hartnup, Katie. "Sperm Competition in the Fruit Fly". Drosophilia pseudoobscura. |
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* Alcock, John 1998. ''Animal Behavior''. Sixth Edition. 429-519. |
* Alcock, John 1998. ''Animal Behavior''. Sixth Edition. 429-519. |
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* Baker, Robin 1996. ''Sperm Wars: The Science of Sex'' ISBN 0-7881-6004-4. |
* Baker, Robin 1996. ''Sperm Wars: The Science of Sex'' ISBN 0-7881-6004-4. |
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Revision as of 22:52, 1 April 2008
The goal of evolution for all organisms is reproduction to ensure their genes are inherited by the next generation. From the male’s perspective, they face many struggles when attempting this. Males transfer sperm to the female that are inexpensive to produce. This means that males have the capacity of producing large numbers of sperm and can fertilize a large number of eggs as well. In certain situations males might have limited access to females and those females may also be promiscuous, then the result is competition with other males. This competition will not only be for access to those females but also to fertilise the eggs of the females they mate with. This concept is referred to as is Sperm Competition. Sperm competition is "competition between sperm of two or more males for the fertilization of an ovum" (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). Male fruit flies have been shown to release 250% more sperm when another male is present, compared to being alone with the female (Gage 1991).
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). These sorts of competition can occur within a single male, if they involve genes that are expressed in the haploid sperm itself. The male black-winged damselfly provides a prime example of sperm competition. Female black-winged damselflies are known to mate with several males over the span of a only a few hours and therefore posses a receptacle known as a spermatheca which stores the sperm. During the process of mating the male damselfly will pump his abdomen up and down using his specially adapted penis which acts as a scrub brush to remove the sperm of another male. This method proves quite succesful and the male damselfly has been known to remove 90-100 percent of the competing sperm (Alcock 1998).
Sperm competition has led to other adaptations such as larger ejaculates, prolonged copulation, deposition of a copulatory plug, or the application of pheromones that reduce the female's attractiveness.
The adaptation of sperm traits, such as length, viability and velocity might be constrained by the influence of cytoplasmic DNA (i.e. mitochondrial DNA) (Dowling et al 2007).
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
External links
References
- Hartnup, Katie. "Sperm Competition in the Fruit Fly". Drosophilia pseudoobscura.
- Alcock, John 1998. Animal Behavior. Sixth Edition. 429-519.
- Baker, Robin 1996. Sperm Wars: The Science of Sex ISBN 0-7881-6004-4.
- Eberhard, William 1996 Female Control: Sexual Selection by Cryptic Female Choice ISBN 0691010846
- Dowling, Damian K., Larkeson Nowostawski, Albert & Arngqvist, Göran 2007. Effects of cytoplasmic genes on sperm viability and sperm morphology in a seed beetle: implications for sperm competition theory? Journal of Evolutionary Biology 20: 358-368.
- Harcourt, A.H., Harvey, P.H., Larson, S.G., & 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 0-387-28036-7.
- 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.
- Freeman, Scott; Herron, Jon C.; (2007). Evolutionary Analysis (4th ed.). Pearson Education, Inc. ISBN 0-13-227584-8.
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