PREY SIZE, SOCIAL COMPETITION, AND THE DEVELOPMENT OF REPRODUCTIVE DIVISION-OF-LABOR IN SOCIAL SPIDER GROUPS

It has been suggested that the cooperatively social spider, Anelosimus eximius, is eusocial. It has overlapping generations and cooperative brood care, and some females in colonies never reproduce. The hypothesis that the reproductive division of labor arises because of social competition over large prey was tested. Groups of sibling females were provided two types of prey that differed primarily in size. The absolute amount of each type of prey provided fell into three categories. The timing of molt to adulthood and subsequent production of egg sacs was monitored. More spiders molted to adulthood on small fruit flies than on larger house-flies, but the spiders that made it to adulthood in the groups fed larger prey grew larger and produced more egg sacs than the adults on fruit flies at all prey levels. These data suggest that the cooperative capture of large prey in natural colonies influences the formation of a dominant-subordinate dichotomy in which dominants are able to monopolize the resources and secure sufficient resources to reproduce. This system may be important to colony survival because it allows some reproduction to take place even at low prey availability. Likewise, it is possible to envisage such a system's being important to the evolution of the more complex reproductive division of labor with fixed reproductive and nonreproductive castes.