Sexual competition stimulates premature and repeated ejaculation in a mammal

Changing tactics in the face of competition is a strategy in boardrooms--and bars--the world over. New research suggests that when it comes to mating, even the lowly house mouse has the ability to modify its approach in the face of competition. By comparing the behavior of wild house mice in the presence or absence of sexual rivals, new research shows that males of this species have evolved the ability to adapt their copulatory behavior according to the perceived risk that females will mate promiscuously. The findings, which shed light on the evolution of mammalian copulatory behavior, are reported in the April 4th issue of Current Biology by Brian Preston and Paula Stockley of the University of Liverpool.

The sexual behavior of mammals is strikingly diverse, and in many species it involves complex and protracted bouts of copulation, the evolutionary significance of which is not well understood. Protracted copulation can be important to numerous aspects of normal female reproduction; however, physiological studies have suggested that it may also provide males with an advantage in sexual competition by curbing females' re-mating behavior and increasing or spreading the transfer of sperm.

In the new work, researchers show that elevating the perceived risk that male house mice will encounter sexual competition causes them to adjust key aspects of their copulatory behavior. When a sexual competitor was present, males thrusted more vigorously during copulation, ejaculated after 50% less penile stimulation, and were nearly twice as likely to ejaculate on a second occasion. In doing so, males may ensure against the loss of insemination opportunities and are likely to increase their paternity share if females copulated with the rival males.

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Brian T. Preston and Paula Stockley of the University of Liverpool in Leahurst, United Kingdom.

Preston et al.: "Correspondence: The prospect of sexual competition stimulates premature and repeated ejaculation in a mammal." Publishing in Current Biology 16, R239-R241, April 4, 2006. www.current-biology.com


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