HAUBER, ME; LACEY, EA; Univ. of California, Berkeley: Bateman�s Principle in Social Mammals: The Influence of Cooperative Breeding on Variance in Female and Male Reproductive Success

Sex-specific slopes of Bateman gradient curves have important implications for reproductive behavior, including patterns of sexual selection and reproductive competition among conspecifics. In general, intersexual differences in the fitness benefits derived from mating with multiple partners are expected to lead to distinct patterns of variance in reproductive success for males and females, with variance in direct fitness typically being greater among males. Data from social mammals, however, suggest that in group-living species with non-breeding alloparents, this pattern may be reversed such that variance in reproductive success is greater among females. Using genetic estimates of parentage and reproductive success obtained from the literature, we explore this apparent contradiction of Bateman�s original findings. Our analyses indicate that social interactions, including social suppression of reproduction, are powerful determinants of individual direct fitness. Specifically, these data suggest that the greater variance in reproductive success among females in cooperatively breeding species of mammals represents an example of how social factors may override sex-specific patterns of fitness, rather than a refutation of the fundamental implications of Bateman�s work regarding gender roles. We suggest that further study of interactions between gender, social system, and variance in direct fitness will yield important new insights into the ways in which social environment modifies reproductive competition and sexual selection in vertebrates.