Genetic consequences of mammalian social structure

Populations of social mammals are characterized by several demographic feat ures that may increase the magnitude of genetic drift relative to other evo lutionary forces. In particular, polygynous mating and socially mediated co nstraints on gene flow have been proposed to foster random genetic differen tiation among social groups, thereby accelerating rates of evolutionary cha nge. To evaluate this hypothesized link between sociality and genetic subdi vision, I examined results of published studies of mammalian populations in which genetic structuring was assessed at the level of social groups. Popu lation genetic data from a taxonomically diverse array of social mammals re vealed low to moderately high levels of genetic differentiation among socia l groups (F-ST = 0.006-0.227), coupled with consistently high levels of wit hin-group heterozygosity indicated by negative F-IS-values. Relatively high er levels of genetic structuring were observed in populations in which samp ling effects associated with polygynous mating were reinforced by female ph ilopatry. The degree of genetic subdivision observed in several taxa, most notably black-tailed prairie dogs (Cynomys ludovicianus) and red howler mon keys (Alouatta seniculus), indicated that social organization can have a pr ofound impact on population genetic structure. However, in most cases, soci al barriers to gene flow are likely insufficient to promote the degree of g enetic subdivision and inbreeding envisioned by models of rapid drift-induc ed speciation. It appears that social mammals generally are characterized b y a dynamic non-equilibrium mode of population structure in which local dem es are characterized simultaneously by small variance effective sizes and l arge inbreeding effective sizes.