Why do female adders copulate so frequently?
Thomas Madsen*†, Richard Shine†‡, Jon
Loman* & Thomas Håkansson§
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,
‡To whom all correspondence should be
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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