The effect of octopamine, body size, and ovarian development on caste-characteristic behavior in the facultatively eusocial and solitary bees Megalopta (Hymenoptera: Halictidae)

Abstract

In eusocial species, workers forfeit their ability to reproduce in order to assist the queen in raising offspring. In the facultatively eusocial and solitary bee, Megalopta genalis, queens recruit workers by aggressively dominating their daughters. However, the neurobiological mechanism that underlies this behavior and the emergence of new social phenotypes has not been studied. I observed the effect of the biogenic amine, octopamine (OA), on caste-characteristic aggression in queens, workers, and solitary foundresses, using a circle tube apparatus. Additionally, I compared the effects of body size and ovarian development on behavior in social and solitary females. Although OA did not have a significant effect, I found that in social pairs, a bee’s behavior predicted its partner’s when these interactions were worker-like. Furthermore, data shows that ovarian development, but not head size, predicted caste-characteristic behavior in workers, while the opposite was true for solitaries; larger head size, but not ovary size, was associated with queen-like behavior. These findings support the hypothesis that queens influence the behavior and physiology of their daughters. Notably, they also suggest that distinct mechanisms determine dominant and submissive interactions in social and solitary females.