The effect of sex-allocation biasing on the evolution of worker policing in hymenopteran societies

Mutual policing is thought to be important in conflict suppression at all l evels of biological organization. In hymenopteran societies (bees, ants, an d wasps), multiple mating by queens favors mutual policing of male producti on among workers (worker policing). However, worker policing of male produc tion is proving to be more widespread than predicted by relatedness pattern s, occurring in societies headed by single-mated queens in which, paradoxic ally, workers are more related to the workers' sons that they kill than the queen's sons that they spare. Here we develop an inclusive-fitness model t o show that a second reproductive conflict, the conflict over sex allocatio n, can explain the evolution of worker policing contrary to relatedness pre dictions. Among ants, and probably other social Hymenoptera, workers kill m ales to favor their more related sisters. Importantly, males are killed at the larval stage, presumably because workers cannot determine the sex of qu een-laid eggs. Sex-allocation biasing favors worker policing because polici ng removes some males (the workers' sons) at low cost at the egg stage rath er than at higher cost at the larval stage. Our model reveals an important interaction between two reproductive conflicts in which the presence of one conflict (sex allocation) favors the suppression of the other (male produc tion by workers).