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Letters to Nature
Nature 355, 440 - 441 (30 January 2002); doi:10.1038/355440a0

Why do female adders copulate so frequently?

Thomas Madsen*, Richard Shine, Jon  Loman* & Thomas Håkansson§

*Department of Animal Ecology, University of Lund, S 223 62 Lund, Sweden
Zoology Department, The University of Sydney, New South Wales 2006, Australia
§ Department of Anthropology, University of Kentucky, Lexington, Kentucky 40506, USA
To whom all correspondence should be addressed.

MALES of most animal species will enhance their reproductive success if they mate often and with many different partners, whereas promiscuous mating is unlikely to increase a female's reproductive success. Why then is multiple copulation by females so common1–6? Many theoreticians have suggested that multiple copulations might enhance the viability of a female's offspring, either because of inadequate quantities of sperm from the first mating1,7, additional nutrients derived from the seminal fluid7,8 or some genetic advantage9–14. Our field studies on Swedish adders provide the first empirical evidence that multiple copulations, with different partners each time, increase offspring viability. This advantage apparently results from more intense sperm competition in the female's reproductive tract, resulting in a higher proportion of her ova being fertilized by genetically superior males.



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