Behaviour: 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 have strongly female-based sex allocation. When added to previous studies, our findings show that sociality is well developed in all major clades of the allodapines, adding support to the notion that sociality is an ancestral trait of the allodapines. This indicates that extant members of the Allodapini do not represent early stages of social evolution and that forms of sociality have frequently reached very complex levels within the tribe. © 2007 Entomological Society of America.