Phylogenetic relationships of corbiculate bees (Hymenoptera: Apidae: Apini)

Abstract

Bees are aculeate hymenopterans which, all together, comprise approximately 19,000 valid species, which are divided into seven families, among which Apidae is one of the best known groups and that hosts, for example, the honey-bee (genus Apis). In addition to the species richness of bees, a remarkable diversity of social behaviors is known to exist within this group, comprising species that are obligatorily solitary (over 80% of all bee species), taxa with some level of social interaction, and groups showing highly sophisticated behaviors related to life in society. One of the most fascinating groups of bees in this respect is that of corbiculate bees (Apidae: Apinae: Apini), subdivided into four subtribes, three of which are eusocial, characterized by division of labor, cooperative brood care, caste differentiation, and superposition of generations. The name "corbiculate bees" refers to a morphological trait exclusive to the tribe Apini, the corbicula, a modification of female hind-legs important for pollen transport to the nest. The four subtribes of Apini are the following: Apina (honey-bees), Meliponina (stingless bees), Bombina (bumble-bees), and Euglossina (orchid-bees). Among these taxa, Apina and Meliponina comprise the so-called "advanced eusocial" groups. Phylogenetic relationships among corbiculate bees have been under intense controversy for the last two decades, thus hampering a robust understanding of evolution of eusociality. Overall, most hypotheses based on morphological and behavioral data point to a monophyletic group that unites Apina and Meliponina together, therefore indicating a single origin of advanced eusocial behaviors. Molecular datasets (DNA sequence data, primarily), on the other hand, consistently indicated independent origins for this behavior. The main goal of this project is to re-evaluate the phylogenetic relationships among the major lineages of corbiculate bees. This will be pursued by assembling a comprehensive morphological data-set, including traditional characters as well as new data from the internal skeletal morphology, a rich but largely neglected source of phylogenetic information. Novel morphological characters generated in this study will also be cladistically analyzed simultaneously with previously proposed morphological characters, molecular and behavioral data sets. This research will make possible a deeper and more robust understanding of the origin and evolution of eusocial behavior within the corbiculate bee clade. (AU)