Molecular phylogenetics of allodapine bees, with implications for the evolution of sociality and progressive rearing

Allodapine bees have long been regarded as providing useful material for examining the origins of social behavior. Previous researchers have assumed that sociality arose within the Allodapini and have linked the evolution of sociality to a transition from mass provisioning to progressive provisioning of brood. Early phylogenetic studies of allodapines were based on morphological and life-history data, but critical aspects of these studies relied on small character sets, where the polarity and coding of characters is problematic. We used nucleotide sequence data from one nuclear and two mitochondrial gene fragments to examine phylogenetic structure among nine allodapine genera. Our data set comprised 1506 nucleotide positions, of which 402 were parsimony informative. Maximum parsimony, log determinant, and maximum likelihood analyses produced highly similar phylogenetic topologies, and all analyses indicated that the tropical African genus Macrogalea was the sister group to all other allodapines. This finding conflicts with that of previous studies, in which Compsomelissa + Halterapis formed the most basal group. Changing the basal node of the Allodapini has major consequences for understanding evolution in this tribe. Our results cast doubt on the previous hypotheses that progressive provisioning and castelike social behavior evolved among lineages leading to the extant allodapine taxa. Instead, our results suggest that mass provisioning in Halterapis is a derived feature and that social behavior is an ancestral trait for all allodapine lineages. The forms of social behavior present in extant allodapines are likely to have resulted from a long evolutionary history, which may help explain the complexity of social traits found in many allodapine bees.