Unrelated males in colonies of facultatively social bee

Abstract

Colonies of social Hymenoptera are usually groups of closely related females, in which the dominant female(s) is specialized for reproduction and subordinate females care for immature offspring. Kin selection is thought to be the main factor that supports social cohesion. We have discovered a simple society of the bee Ceratina chalybea with an average of 4.68 colony members that cannot be maintained by kin selection alone. These colonies consisted of old reproductive female, young adults and provisioned brood cells. About half of young adults are unrelated to the old female, and almost all of the young adults are male. The old female provisions new brood cells, while continuing to feed young adult offspring. As young adults do not perform demanding or risky activities, they incur little or no cost, but they do benefit from the food they obtain from the old female.