The adaptive advantage of prolonged mating: a test of alternative hypotheses

When a female can mate with more than one male, males are thought to reduce intrasexual competition by prolonging mating, that is, mating longer than necessary for sperm release. Two principal hypotheses have been proposed to explain the advantage of prolonged mating. The extended mate guarding hypothesis suggests that with longer mating, the female is less likely to be inseminated by another male. The ejaculate transfer hypothesis suggests that with longer mating, more of the male's sperm are stored. To our knowledge, this is the first study to test these alternatives simultaneously by manipulating duration of mating and examining effects on sperm release, storage and female polyandry. We found support for the mate guarding hypothesis in the golden orb-weaving spider Nephila clavipes; the longer the mating with the first male, the lower the likelihood of the female copulating with another male. This was not due to influence on female receptivity but on the ability of subsequent males to couple. Inconsistent with the ejaculate transfer hypothesis was the observation that duration of mating with the first male did not linearly correlate with release or storage of its sperm. We suggest that prolonged mating does not result in sexual conflict in this species.