Knowing who's who: nestmate recognition in the facultatively social carpenter bee, Xylocopa virginica

Abstract

When animals live in groups, the ability to discriminate group members from nonmembers allows individuals to adjust their behaviour in ways that enhance both individual and group fitness. In social insects, especially bees, this kind of recognition has mainly been studied with reference to colony-based social interactions, but they also interact in other kinds of group contexts. In the facultatively social carpenter bee, Xylocopa virginica, individuals of both sexes interact repeatedly, in such activities as cooperative brood raising by females, territorial competition by males, and matings near nest entrances. In light of these varied interactions, in which the ability to discriminate familiar from unfamiliar individuals might be advantageous, the aim of our study was to determine whether X. virginica adults are capable of nestmate recognition. Nestmates were defined operationally as bees that were caught at the same nest entrance after spending the night together, whereas non-nestmates were from different nests. We used circle tube assays of male–male, female–female and male–female dyads to compare rates of aggressive (pushing, biting and C-postures) and tolerant/cooperative (head-to-head touching and passing) behaviour in nestmates versus non-nestmates. In general, aggression occurred sooner and more frequently among non-nestmates than among nestmates, whereas tolerance was more common among nestmates. This indicates that male and female bees can recognize familiar individuals of both sexes and adjust their behaviour accordingly. Since tested individuals may have been nestmates for less than 24 h, this further suggests that both female and male bees may learn the identities of their nestmates quickly.