THE INFLUENCE OF DISPERSAL PATTERNS AND MATING SYSTEM ON GENETIC DIFFERENTIATION WITHIN AND BETWEEN POPULATIONS OF THE RED HOWLER MONKEY (ALOUATTA SENICULUS).

The relationship between social structure and partitioning of genetic variance was examined in two red howler monkey populations (W and G) in Venezuela, one of which (G) was undergoing rapid growth through colonization by new troops. Rates and patterns of gene flow had been determined through radiotelemetry and direct observation data on solitary migrants, and 10 years of troop censusing. Standard electrophoresis techniques were used to examine 29 loci in blood samples taken from 137 of the study animals. Analysis of genetic variance demonstrated: (1) a significantly high level of genetic variation among troops within populations (F = 0.225 for W and 0.142 for G), and (2) a significant excess of heterozygosity within troops relative to expected (F = -0.136 for W and -0.064 for G), despite relatively high levels of observed and inferred inbreeding in W. Differences between the populations in F values conformed to those predicted based on differences in colonization rate. Comparison of partitioning of genetic variance among different genealogical subsets of troops demonstrated that the pattern of genetic differentiation observed among troops within populations was promoted by an essentially single-male harem breeding structure, a very low rate of random exchange of breeding males among troops, and a high degree of relatedness among troop females. Between-troop genetic differentiation (F ) was thereby increased relative to that expected from other types of social organization, while the correlation between uniting gametes within troops (F ) was decreased. Genetic differentiation between populations (2%) corresponded to that predicted from migration rates. Such a mosaic of genetic variation, combined with differences in reproductive success observed among troops and a high troop failure rate, create conditions in which interdemic selection could result in more rapid spread of advantageous gene combinations than would be expected in a panmictic population, particularly in a colonizing situation in which the founder population is small.