Reproductive inefficiency and increased behavioral variation are associated with large group size in the orchid bee, Euglossa dilemma

Abstract

Orchid bees are the only corbiculate bee lineage that is not obligately eusocial. However, multiple species of orchid bee show facultative sociality, with reproductive division of labor and a social hierarchy effectively enforced by oophagy. Orchid bee species differ in the degree of reproductive skew in social groups, as well as the rigidity of social roles. In the orchid bee Euglossa dilemma, previous observation of social groups of two or three individuals found that reproductive skew was complete, with one clear dominant individual that ate and replaced each subordinate laid egg. Here, we compare patterns of egg laying and egg-replacement between typical social nests of 2–3 individuals and larger social nests of 4–5 individuals. We find a striking difference in the reproductive behavior of colonies of varying group size; larger nests exhibit more reproductive inefficiency and conflict over the dominant social position, characterized by repeated oophagy and slower egg replacement. Our findings are consistent with the hypothesis that group size in E. dilemma may be limited by the ability of dominant bees to keep up with egg replacement. We discuss the possible causes and consequences of observed behavioral variation and its implications for understanding social behavior in orchid bees.