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Meaningless sex? Male mounting reduces sexual promiscuity of females

Fakery is seen throughout the animal kingdom and is especially evident in the realm of mate selection and mating behavior. A puzzling behavior frequently observed in many species is copulation between males and females without the delivery of semen. In a world where reproduction is key to a species, survival, such behavior poses a real mystery. In a study that sheds new light on the evolution of sexual behavior, researchers have utilized a novel technique to reveal that in feral chickens, the simple stimulus generated by male mounting--in the absence of actual insemination--reduces the sexual promiscuity of a hen, indicating that even copulations that do not result in semen transfer may be crucial to defend the paternity of a male.

Females of many species often copulate with multiple males, leading to the phenomenon of sperm competition--the competition between the ejaculates of different males to successfully fertilize eggs. The battles of sperm competition occur at the cellular and molecular levels and involve the production of sperm-associated substances that boost the competitiveness of a male's sperm; however, the production of these substances comes at an energetic cost to males. Males who can avoid such costs--and still successfully mate--may be at a reproductive advantage. Therefore, in some species, males may avoid sperm competition by preventing females from mating with other males. However, previous studies have not fully considered the possibility that female promiscuity may be inhibited by stimuli generated by the simple act of male mounting.

In the new study, a team of researchers led by Dr. Tommaso Pizzari of the University of Oxford tested this idea in the feral chicken, a sexually promiscuous species. By using a novel but technologically simple technique--fitting some hens with a light plastic harness covering their cloaca and thus preventing insemination--the researchers were able to separate the effect of insemination products fro
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Contact: Heidi Hardman
hhardman@cell.com
1-617-397-2879
Cell Press
11-Jul-2005


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