Correlated evolution of mating behaviour and morphology in large carpenter bees (Xylocopa)

Carpenter bees (Xylocopa) display variation in mating strategies. In several subgenera males defend territories that contain resources for females. In other subgenera males defend a small non-resource territory. Here, we investigate the correlation between three morphological traits and mating strategy. We found associations between mating strategy and male eye size, size of the mesosomal gland and sexual colour dimorphism, as well as correlative evolution between the morphological characters. Analysis of the evolutionary pathways shows that resource defence, small glands and monomorphic sexes are ancestral states. Increases in gland size seem to precede or coincide with changes in mating behaviour, but changes towards sexual dimorphism follow changes in mating behaviour. Once a non-resource defence strategy with correlated morphology has evolved there are no reversals to the ancestral states. We discuss the types of selection that may have caused these correlative changes.