Male size does not affect territorial behaviour and life history traits in a sphecid wasp

Abstract

The optimum maternal investment per offspring is determined by the relationship between the investment per offspring and offspring fitness. In the European beewolf, Philanthus triangulum, a solitary mass-provisioning sphecid wasp, offspring size correlates with the amount of provisions. We investigated whether the reproductive success of adult males depends on body size in a way that would influence the allocation of parental investment. Since the mating success ofP.triangulum males cannot be determined by observation in the field, we assessed the influence of male size on characteristics of their territories, territorial behaviour and life history traits. Territory size was weakly correlated with male size, but a measure of territory quality (number of female nests in the vicinity) was independent of male size. Neither the duration of ownership nor the intensity of scent marking was correlated with male size. Territory owners were slightly smaller than nonterritorial males. The absolute amount of fat was positively correlated with size but, owing to allometric relationships, the energetic equivalent of the fat store appeared to be independent of size. Life span was not significantly influenced by body size under four different conditions (with and without food in the laboratory, in an outdoor flight cage and in the field). We discuss the discrepancy between these results and other studies that have mostly reported advantages to large males. We suggest that in noncontact male–male interactions, as seen in the European beewolf, body size might not be the key determinant for success in contests. We conclude that there is no evidence for a strong size dependence of male reproductive success. Thus the reproductive success of male progeny probably does not depend on parental investment in a way that would influence the investment allocation of females.