Comprehensive phylogeny of apid bees reveals the evolutionary origins and antiquity of cleptoparasitism.

Apidae is the most speciose and behaviorally diverse family of bees. It includes solitary, eusocial, socially parasitic, and an exceptionally high proportion of cleptoparasitic species. Cleptoparasitic bees, which are brood parasites in the nests of other bees, have long caused problems in resolving the phylogenetic relationships within Apidae based on morphological data because of the tendency for parasites to converge on a suite of traits, making it difficult to differentiate similarity caused by common ancestry from convergence. Here, we resolve the evolutionary history of apid cleptoparasitism by conducting a detailed, comprehensive molecular phylogenetic analysis of all 33 apid tribes (based on 190 species), including representatives from every hypothesized origin of cleptoparasitism. Based on Bayesian ancestral state reconstruction, we show that cleptoparasitism has arisen just four times in Apidae, which is fewer times than previously estimated. Our results indicate that 99% of cleptoparasitic apid bees form a monophyletic group. Divergence time estimates reveal that cleptoparasitism is an ancient behavior in bees that first evolved in the late Cretaceous 95 Mya [95% highest posterior density (HPD) = 87-103]. Our phylogenetic analysis of the Apidae sheds light on the macroevolution of a bee family that is of evolutionary, ecological, and economic importance.