Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection

The nuptial prey gift in the spider Pisaura mirabilis has been suggested to function as a male protection against sexual cannibalism during courtship and mating. This hypothesis together with two alternatives-male mating effort and paternal investment hypotheses-were tested in a laboratory experiment with sexually inexperienced males and females. One group of males offered no gift to the female while three groups of males offered small, medium, or large sized gifts, respectively. No male was cannibalized among 82 trials. Aggression was observed only in encounters where a gift was presented. Males without a gift courted females, and 40% of these males managed to copulate, compared to 90% of males offering a gift. The copulation duration was positively correlated with gift size. In general, the female terminated the copulation and ran away with the gift. The proportion of eggs fertilized increased with copulation time. Presence or size of the nuptial gift did not affect female fecundity or spiderling size significantly. The results refute the hypotheses of sexual cannibalism and paternal investment. The nuptial gift represents a male mating effort; it entices the female to copulate, facilitates coupling during copulation, and by prolonging copulation it may increase the amount of sperm transferred. I conclude that the nuptial prey gift in Pisaura mirabilis is maintained by sexual selection.