Evolution of Testis Size

Science  16 Feb 2001:
Vol. 291, Issue 5507, pp. 1159
DOI: 10.1126/science.291.5507.1159d

When female animals are inseminated by more than one male, competition amongst sperm ensues. Strength in numbers is key: males that produce more sperm tend to achieve more fertilizations in these contests. Theory predicts that larger testis size should evolve where the risk of sperm competition is greatest. Hosken and Ward test this prediction in the yellow dung fly Scathophaga stercoraria, a species which is to sperm competition what Drosophila is to genetics. Flies were bred for ten generations in either polygamous (polyandrous) or monogamous conditions. Under polyandrous conditions, where sperm competition was greater, there was, independent of body size, an increase in testis size. — AMS

Ecol. Lett.4, 10 (2001).

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