Sociality in Amphylaeus morosus (Hymenoptera : Colletidae : Hylaeinae)

To date, social nesting has been relatively unknown in the bee family Colle tidae. Same-generation females of the bee Amphylaeus morosus Smith frequent ly share tubular nests where only 1 brood cell can be provisioned at a time . In montane eucalypt forests of southern Australia A. morosus nests are co nstructed within naturally excised fronds of the rough tree fern, Cyathea a ustralis. In these habitats, the species is univoltine with adult eclosion occurring in late summer. Dispersal from overwintering nests and new nest i nitiation begins in spring, and all new nests contain only 1 adult female. However, a significant proportion of old, reused nests during the brood-rea ring phase contain 2 or 3 adult females that are mated with mature ovaries (approximate to 23% of all inhabited nests). Per capita brood production wa s statistically higher in reused. versus new nests, probably because the fo rmer start their cell provisioning earlier. Per capita brood production was not statistically higher in two- versus one-female reused nests, although there were trends in this direction and earlier adult female mortality may have obscured end-of-season patterns. Brood parasitization by a gasteruptii d wasp (Casteruption sp.) was statistically higher in new nests than two-fe male reused nests, but only marginally higher in one- versus two-female reu sed nests. Average relatedness among adult females in multifemale nests was quite low (r = 0.26 +/- 0.06 SE). Hence, kin selection is unlikely to be a major factor selecting for cooperative nesting in this species. Cell provi sioning patterns in A. morosus could lead to nestmates conflicting over for aging effort and reproduction. No evidence for reproductive division of lab or or foraging specialization among nestmates was found, however, and their relative body sizes, ovary sizes, and wing wear were not significantly dif ferent from statistical expectation. Therefore, sociality in A. morosus pro bably results from the benefits of sharing a valuable resource (i.e., a pre existing nest) and avoiding dispersal costs, rather than cooperation per se . Nevertheless, the prospects for nestmate cheating are high. High-resoluti on genetic studies could determine if the apparent lack of reproductive ske w, based on dissection data reflects brood maternity. Sociality in A. moros us provides an ideal opportunity to investigate reproductive skew theories.