MUTUALISTIC BENEFITS GENERATE AN UNEQUAL DISTRIBUTION OF RISKY ACTIVITIES AMONG UNRELATED GROUP MEMBERS

Recent studies provide a new challenge to the adequacy of theories con cerning the evolution of cooperation among nonrelatives: some individu als perform high-risk activities while others do not. We examined a co mmunal hymenopteran species, Lasioglossum (Chilalictus) hemichalceum, to determine why group members engaged in demonstrably risky activitie s (foraging) tolerate the selfish behavior (remaining in the nest) of unrelated nestmates. Experimental removal of adult females indicated t hat their presence is required for the protection of brood from ant pr edators. Nonforagers ensure the continued presence of adults in the ne st if the risk-taking foragers die, thereby safeguarding the survival of forager offspring. This results in an unequal distribution of risky activities within social groups in which avoidance of risky activitie s by some group members is ultimately beneficial to risk takers.