Social Dispersion and Genetic Variation in Two Species of Emballonurid Bats

and Summary Saccopteryx leptura and S. bilineata are closely related, sympacric species of neotropical bats that exhibit marked differences in social organization and dispersion patterns. S. leptura is monogamous and roosts in small groups of 1 to 5 (Y = 2.6) individuals that are finely dispersed. S. bilineata is harem-polygamous and roosts in larger groups of 1 to 42 (Y = 8.1) individuals that are more coarsely dispersed. Allozyme genetic studies of individuals from Trinidad, W I. demonstrate that both species carry similar, high levels of polymorphism and heterozygosity. Although significant genetic heterogeneity was observed among geographical populations of S. leptura, there is no evidence for either species that social structuring leads to inbreeding and the loss of heterozygosity, or that it promotes the development of genetic heterogeneity among social units that could accelerate the evolutionary diversification of these taxa. These results do not support a recently proposed hypothesis that social structuring in mammals has these effects. Observed intercolony genetic heterogeneity among adult males resident in multimale groups of S. bilineata is greater than intercolony heterogeneity of adult females. This is an apparent result of female dispersal and the recruitment of males into their parental groups. These results suggest that the adult males within large colonies may be kin-related.