Effects of Demographic Change on Group Kin Structure and Gene Dynamics of Populations of Red Howling Monkeys

Four populations of red howling monkeys (Alouatta seniculus) in different states of population growth were studied to examine how changes in intrasexual competition and kin availability influence mating patterns and population genetic structure. The demography of each population was monitored for 5 years. Genetic variance within and between groups and coefficients of relatedness (r) were estimated from allozyme loci. Advantages of cooperating with kin over non-kin changed with different demographic circumstances for each sex, such that social groups were more likely to be kin groups when population density was approaching or at carrying capacity than when it was low. In populations growing rapidly through new social group formation, genetic differentiation between groups was low. Genetic differentiation increased as populations approached carrying capacity and groups matured socially (i.e., r increased). That trend was reversed as r within group breeding subsets (males and females, respectively) increased, thereby decreasing r between males and females and reducing group r. This was enhanced when inbreeding within groups was