Affiliative and agonistic interactions distinguish sex-biased social groups of greater spear-nosed bats, Phyllostomus hastatus.

The social environment, and the interactions that comprise it, can have a profound influence on reproductive success and survival. Yet not all individuals experience the social environment in the same way. In polygynous species wherein males and females experience different competitive environments, sex may be an important factor in shaping the degree to which the social environment serves as a source of support or stress. We investigated patterns of affiliative and agonistic interactions in the highly polygynous greater spear-nosed bat (Phylostomus hastatus), in which sex-biased social niches may be associated with dramatic female-biased survival, to quantify the extent to which these highly sex-biased social environments differed. Agonistic interactions in male-biased bachelor groups were more frequent and longer in duration than those seen in harem groups. Agonistic interactions also differed qualitatively, with bachelor males almost exclusively engaging in dyadic fights in which they deployed highly physical behaviors, such as "wing-locks", rarely observed between females. By contrast, allogrooming was only observed between females in harem groups, particularly before emergence in the evening and upon return to the roost. Taken together, these data suggest that the patterns of social interaction in harem and bachelor groups differ in their valence and intensity, with individuals living in bachelor groups experiencing a social environment characterized by more intense aggression without the positive interactions seen between females in harem groups. We hypothesize that these behavioral differences contribute to the sex-biased differences in allostatic load and survival observed in this species.