Kin presence drives philopatry and social aggregation in juvenile Desert Night Lizards (Xantusia vigilis)

Kin selection is a powerful concept in evolutionary biology that can explain both cooperative and competitive behavior. Most social behavior associated with kin selection depends on prior dispersal decisions by juveniles, which can choose to either disperse away from kin or remain at the natal site. A useful way to investigate the role of kin in social behavior is to experimentally manipulate kin environment and resolve a direct causal relationship between kin presence, dispersal strategy, and subsequent social behavior. I used a cross-fostering experiment to manipulate the relatedness of the social environment in both the laboratory and the field and test for the effects of kin on juvenile dispersal and social aggregation in the Desert Night Lizard (Xantusia vigilis). I found that kin presence actively promotes both philopatry and winter aggregation, which is consistent with the predictions of kin cooperation and suggests that kin sociality in this species is not simply a by-product of limited dispersal. In combination with kin effects known in other species, these results suggest a generality of positive associations with kin, the potential dominance of cooperative over competitive mechanisms, and the increased prominence that cooperation may have in the future theoretical study of kin selection.