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

The optimum maternal investment per offspring is determined by the relation ship between the investment per offspring and offspring fitness. In the Eur opean beewolf, Philanthus triangulum, a solitary mass-provisioning sphecid wasp, offspring size correlates with the amount of provisions. We investiga ted whether the reproductive success of adult males depends on body size in a way that would influence the allocation of parental investment. Since th e mating success of P. 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. Territor y size was weakly correlated with male size, but a measure of territory qua lity (number of female nests in the vicinity) was independent of male size. Neither the duration of ownership nor the intensity of scent marking was c orrelated with male size. Territory owners were slightly smaller than nonte rritorial males. The absolute amount of fat was positively correlated with size but, owing to allometric relationships, the energetic equivalent of th e fat store appeared to be independent of size. Life span was not significa ntly influenced by body size under four different conditions (with and with out 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 ma le-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 n o evidence for a strong size dependence of male reproductive success. Thus the reproductive success of male progeny probably does not depend on parent al investment in a way that would influence the investment allocation of fe males. (C) 2000 The Association for the Study of Animal Behaviour.