Social trait definitions influence evolutionary inferences: a phylogenetic approach to improving social terminology...

The comparative method relies not only on a good understanding of the phylogenetic relationships among taxa, but also on consistent terminology for describing phenotypes. Clear and consistent terminology allows similar phenotypes to be described and phylogenetically analyzed in different organisms, whereas inconsistent terminology is a major impediment to comparisons, even for taxonomically restricted groups such as bees. Here, I propose that the usefulness of social terminology can be judged by its value in phylogenetic trait-mapping aimed at uncovering evolutionary transitions between solitary and social behavior. I propose a four-step approach to evaluate and update social terminology, in which definitions are first updated based on recent behavioral studies (step 1), mapped onto a phylogeny (step 2), evaluated for their utility in the trait-mapping exercise (step 3), and then, if necessary, revised (step 4). To demonstrate the approach, I define four terms important for understanding social evolution in bees (solitary, social, eusocial, and hypersocial) and map them onto a very recent phylogeny of Apidae. This not only illustrates an objective method for evaluating social terminology, but also provides novel inferences about social evolution in Apidae, including support for a parasocial origin of eusociality and at least two Major Evolutionary Transitions to hypersociality.