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Roosters have a “sperm budget” and can be picky in allocating their limited resources, Tommaso Pizzari and his colleagues at the University of Leeds report in the Nov. 6 Nature. They have discovered that roosters give more sperm to a new mate than to a familiar one, more to females with larger combs, and more when rival males are present.

It’s been assumed that males have a simple sexual strategy of just mating with as many different females as possible, but their behavior has been found to be much more complex to help them maximize their reproductive chances. Females with larger combs lay superior eggs and more of them, and females with suitors also are judged to be better reproductive bets. To up their chances of fertilization, males deposit more sperm with these females.

Pizzari and his colleagues studied feral chickens and red jungle fowl, both species in which females mate with several males. The authors write: “Our results indicate that female promiscuity leads to the evolution of sophisticated male sexual behavior.” How the roosters are able to control the amounts doled out is still unknown, but the problem of fowl sperm collection has obviously been solved.

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 11/11/2003.
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