Kin conflict over caste determination in social Hymenoptera

We argue that caste determination, the process whereby females in the socia l Hymenoptera develop into either queens or workers, is subject to kin-sele cted conflict. Potential conflict arises because developing females are mor e closely related to their would-be offspring than to those of other female s. Therefore, they may favour becoming queens contrary to the interests of other developing females and of existing queens and workers. We suggest two contexts leading to potential caste conflict. The first occurs when queens are reared in a reproductive phase following an ergonomic phase of worker production, while the second occurs when queens and workers are reared simu ltaneously. The first context assumes that workers' per capita contribution to colony survival and productivity falls with rising colony size. A criti cal feature influencing whether potential conflict is realized is the exten t to which developing females can determine their own caste ("self-determin ation"). Self-determination is facilitated when female larvae control their own food intake and when queen-worker size dimorphism is low. We know of n o strong evidence for actual conflict over caste fate arising in the first context. However, stingless bees and polygynous ants with excess queen-pote ntial larvae that are either forced to develop as workers or are culled as adults demonstrate actual caste conflict in the second context. Caste confl ict does not preclude caste regulation for "the good of the colony", but su ch regulation is contingent on either the absence of potential conflict or on developing females losing control of their caste fate.