Sperm Competition in a Nuptial Feeding Spider, Pisaura Mirabilis

Abstract

Abstract The paper tests two hypotheses about sperm priority in the spider Pisaura mirabilis. A 'phylogenetic constraints hypothesis' states that since the females have conduit spermathecae, first male priority should prevail. On the other hand, males offer nuptial prey to the females and females mate with multiple males. The evolution of these traits is most easily understood if late mating males also have a substantial fertilization success. The results indicate a compromise solution. Sterile-male technique with double-mated females indicated a first male priority pattern (P1 = ca 70%, after adjusting for sterilization damage and experimental mortality). However, the success of the fourth male of quadroublemated females was unexpectedly high (adjusted P4 = ca 24%, not different from P of 2 two-male matings). This lends support to a supplementary hypothesis of constant last male success, which may turn an initial first-male advantage into a last-male advantage, when the number of males mating with a female raises above a certain number. Independent of mating order, males may increase their share of fertilizations by long copulation times. It was tested whether female choice for symmetric males might account for differential male success. However, fluctuating asymmetry (FA) in male leg length showed no relationships with fertilization success or copulation duration.