Abstract
Many groups of animals have evolved social behaviours in different forms, from intimate familial associations to the complex eusocial colonies of some insects. The subfamily Xylocopinae, including carpenter bees and their relatives, is a diverse clade exhibiting a wide range of social behaviours, from solitary to obligate eusociality with distinct morphological castes, making them ideal focal taxa in studying the evolution of sociality. We used ultraconserved element data to generate a broadly sampled phylogeny of the Xylocopinae, including several newly sequenced species. We then conducted ancestral state reconstructions on the evolutionary history of sociality in this group under multiple coding models. Our results indicate solitary origins for the Xylocopinae with multiple transitions to sociality across the tree and subsequent reversals to solitary life, demonstrating the lability and dynamic nature of social evolution in carpenter bees. Ultimately, this work clarifies the evolutionary history of the Xylocopinae, and expands our understanding of independent origins and gains and losses of social complexity.