Multiple molecular data sets suggest independent origins of highly eusocial behavior in bees (Hymenoptera:Apinae)

Abstract

Different views of the pattern of social evolution among the highly eusocial bees have arisen as a result of discordance between past molecular and morphology-based phytogenies. Here we present new data and taxa for four molecular data sets and reassess the morphological characters available to date. We show there is no significant character incongruence between four molecular data sets (two nuclear and two mitochondrial), but highly significant character incongruence leads to topological incongruence between the molecular and morphological data. We investigate the effects of using different outgroup combinations to root the estimated tree. We also consider various ways in which biases in the sequence data could be misleading, using several maximum likelihood models, LogDet corrections, and spectral analyses. Ultimately, we concede there is strong discordance between the molecular and morphological data partitions and appropriately apply the conditional combination approach in this case. We also find two equally well supported placements of the root for the molecular trees, one supported by 16S and 28S sequences, the other supported by cytochrome b and opsin. The strength of the evidence leads us to accept two equally well supported hypotheses based on analyses of the molecular data sets. These are the most rigorously supported hypotheses of corbiculate bee relationships at this time, and frame our argument that highly eusocial behavior within the corbiculate bees evolved twice independently.