SOCIAL-BEHAVIOR IN AN AUSTRALIAN ALLODAPINE BEE EXONEURA (BREVINEURA)XANTHOCLYPEATA (HYMENOPTERA, APIDAE)

The allodapine bees are well suited for comparative studies of social evolution because of the wide variation in social behaviour within and between genera. There are three main clades in the endemic Australian genus Exoneura. Two groups (Exoneura sensu stricto and Exoneurella) h ave received extensive study. In this paper we provide the first detai led study of social behaviour in the third group, Brevineura, based on a heathland population of Exoneura (B.) xanthoclypeata Rayment. This species has two seasonal pulses of egg-laying and brood rearing occurs throughout most of the year, including winter. This extended period o f egg-laying and brood development differs from the two other Australi an Exoneura subgenera and provides extensive opportunities for eusocia l like sib-rearing. Dissection data indicate that reproductive differe ntiation among adult nestmates is well developed and dependent on body size, with smaller females being mostly or entirely non-reproductive. Per capita brood production is dramatically higher in multi-female ne sts than in single-female nests and relatedness between adult nestmate s is moderately high (r approximate to 0.5). These two factors suggest that local fitness enhancement may be occurring and our limited sex a llocation data suggest female-biased ratios. Because of the opportunit ies for sib-rearing in this species, local fitness enhancement has the potential to lower selective thresholds for eusociality.