Social Biology of Two Malagasy Halterapis: Evidence That Eusociality Is Plesiomorphic for an Ancient Allodapine Lineage

Abstract The social biology of many species of allodapine bees from diverse genera has been well studied. However, to infer major evolutionary trends within this tribe as well as plesiomorphic traits in deeper phylogenetic nodes, gaps in our knowledge of social strategies within the poorly understood genus Halterapis must first be investigated. The Malagasy members of this genus comprise 17 described species, but nesting and social biology of only one of these species has been described. Here, we present accounts of the social biology of two other species within this clade, namely, Halterapis isaloensis Brooks and Pauly and Halterapis seyrigi (Benoist). Colony sizes ranged from single-female nests to a seven female nest in H. seyrigi and a nine female nest in H. isaloensis. Nests of both species most commonly contained one to three females and approximately one-half of all colonies collected were multifemale. Both species display strong size-based reproductive skew within multifemale nests and seem to hav...