How monkeys see a forest: genetic variation and population genetic structure of two forest primates

The biological traits of different species usually predispose them to dissimilar levels of extinction risk. Accordingly, we analysed genetic variation and population genetic structure of two endangered forest monkeys to determine how they were influenced by habitat change. The Tana River red colobus and mangabey are of similar body size, are sympatric and endemic to forests in Kenya. The mangabey is frugivorous, terrestrial and exhibits female philopatry but the colobus is folivorous, arboreal and both sexes exhibit natal dispersal. We predicted that both species would have low genetic variation due to high genetic drift, and possible inbreeding, because their populations are relatively small and subdivided in forest fragments. Nevertheless, we expected the mangabeys to have a higher genetic variation because they have a larger population, and their higher vagility would enhance gene flow. Thus, we expected a stronger population genetic structure in the colobus because lower vagility would constrain dispersal and increase genetic differentiation. Finally, we expected both species to exhibit isolation by distance due to greater gene flow among populations in close geographic proximity. We genotyped 146 colobus and 76 mangabeys with nine microsatellite markers and found that both species had relatively high heterozygosities but low allelic richness. Furthermore, allelic richness, heterozygosity and genetic differentiation were all higher in the mangabey and only the mangabey exhibited isolation by distance. Taken together, our results suggest that species with divergent behavioral ecologies may exhibit differential vulnerabilities to genetic erosion due to habitat change.