Phylogenetic comparative skeletal morphology of bees (Hymenoptera: Apoidea: Anthophila)

Bees represent a radiation of hymenopteran insects with about 20,000 valid species, and more than 100 million years of evolution, reflected in an impressive morphological and behavioral disparity among its representatives. Despite contributions of previous studies to the current knowledge of bee phylogeny and classification, there still are many taxa in need of deeper investigation. Previous morphological phylogenetic studies relied mostly on characters from the external anatomy, despite internal structures providing relevant information. The present study aimed to explore the wealth of information from external and internal skeletal anatomy of bees in an explicit phylogenetic context. We discussed overall patterns of morphological evolution across bees and the hypothesized morphology of the protobee. A phylogenetic analysis was conducted with 116 species representing all families, subfamilies, 56 tribes, and 111 genera of bees plus 8 apoid wasp outgroups. The morphological study resulted in 394 characters, with about 26% from the internal anatomy. A summary of the main results obtained is presented herein: (Stenotritidae + Colletidae) + (Andrenidae + Halictidae + (Melittidae + (Apidae + Megachilidae))). The morphological evidence supports Melittidae as the sister-group of LT-Bees and Colletidae + Stenotritidae as the sister to all the remaining bees. The placement of these lineages is critical to interpret the evolution of some important morphological complexes and understand the suite of traits probably present in the ancestral protobee. Finally, our results allowed us to provide an updated list of synapomorphies for all recognized families and discuss some key morphological changes across distinct lineages of bees.