Sperm competition tactics shape paternity: adaptive role of extremely long copulations in a wolf spider

Abstract

Polyandry may occur in many species. In spiders when multiple males mate sequentially, conservative anatomical female traits largely, although not entirely, determine whether the first or last male gains precedence in siring the offspring. More flexible behavioural traits show remarkable variation among spiders, including the occurrence of extremely long copulation times. In the wolf spider Pardosa agrestis copulations can last several hours, even though complete fertilization of the female's eggs requires a small fraction of this time. We tested the hypothesis that long copulations in P. agrestis may be a way to overcome a strict first-male precedence, expected from the genital anatomy of female entelegyne spiders. In a large number of mating tests we observed complete and interrupted copulations in both positions of a double mating set-up. Using the sterile male technique we found that paternity was not exclusively determined by the mating order of males; interruption of mating had a dramatic effect on paternity, but did not affect offspring number in a single mating scenario (i.e. the copulation duration was sufficient for the fertilization of all eggs). Females that had an uninterrupted mating were less willing to mate again and became choosy, while females whose first mating was interrupted behaved similarly to virgin females. Also, males seemed to adjust copulation duration to female reproductive status, mating for less time with nonvirgin females, irrespective of whether the female's first mating was interrupted or not. We conclude that extremely long copulations are likely to be an adaptive behaviour manipulating female reproductive behaviour and enabling males to overcome phylogenetically determined limitations in paternity.