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.
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