Behaviour 2019
Low nest fidelity underlies low within-group relatedness in a facultatively social bee 
Madeleine M Ostwald, Romain A Dahan, Zachary Shaffer, Jennifer H. Fewell. Arizona State University, Tempe, Arizona, United States

For the past half century, kin selection theory has served as the dominant paradigm for understanding the evolution of social behavior. However, many animal groups form among non-relatives, and gain no inclusive fitness benefits from cooperating. Carpenter bees are useful candidates for the study of non-kin social evolution due to their flexible sociality and tendency to drift among groups, potentially diluting group relatedness. In this study, we characterized the relatedness and dynamic group membership of the facultatively social carpenter bee, Xylocopa sonorina. We used microsatellite analysis to characterize female genetic relatedness and found no difference between the relatedness within and between groups. Further, we used mark-recapture techniques to assess nest fidelity and found that nest switching behavior was common in this population. Together, these results suggest that low nest fidelity drives association between non-kin, and that nest switching is the mechanism decreasing within-group relatedness. This study provides evidence that factors beyond inclusive fitness, such as ecological constraints, are likely to drive the evolution of social behavior in this species.