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13 April 2006
Mammals Adapt To Win The Sperm Wars
by George Atkinson 
The animal world has lent a whole range of descriptive terms to the language of sexual behavior. Having sex frequently means you're "doing it like rabbits", and our canine companions have, of course, contributed the term "doing it doggie style". But the myriad ways that male mammals choose to copulate is all geared toward one outcome - achieving successful fertilization of the female. Sexual competition is fierce in the animal world and scientists have just discovered a hitherto unknown tactic employed by male mice to increase their sperm's chances of creating a new life. The researchers, from the University of Liverpool in England, have been studying the behavior of wild house mice either in the presence, or absence, of sexual rivals. Their findings, published in the journal Current Biology, show that the male mice have evolved the ability to adapt their mating behavior according to the perceived risk that the females will mate with other males. The researchers say that when male mice perceive sexual competition (other males near the female), they will adjust key aspects of their copulatory behavior. When a sexual competitor was present, males thrusted more vigorously during copulation, ejaculated after 50 percent less penile stimulation, and were nearly twice as likely to ejaculate on a second occasion. All these modification to the sexual act, say the researchers, are aimed at increasing the likelihood of a successful fertilization; and in the final analysis, passing on their genes to another generation. Based on material from Current Biology
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