Incipient signs of genetic differentiation among African elephant populations in fragmenting miombo ecosystems in south-western Tanzania

Abstract

Habitat fragmentation plays a major role in the reduction of genetic diversity among wildlife populations. The African savannah elephant population of the Ruaha-Rungwa and Katavi-Rukwa ecosystems in south-western Tanzania, comprises one of the worlds largest remaining elephant populations, but is increasingly threatened by loss of connectivity and poaching for ivory. We investigate whether there are incipient signs of genetic isolation (loss of heterozygosity) within the younger cohort as a result of habitat loss between the two ecosystems. To investigate the genetic structure of populations, we compared the genotypes for 11 microsatellite loci in the western (n = 81 individuals from Katavi-Rukwa), central (n = 36 individuals from Lukwati and Piti), and eastern populations (n = 193, individuals from Ruaha-Rungwa). We found evidence of significant genetic differentiation among the three populations, but the levels were low, suggesting recent divergence. Furthermore, we identified weak isolation by distance, suggesting higher gene flow among nearer individuals with samples within 50km of each other being more genetically similar to one another than beyond. Although sample sizes were small, a further analysis of genetic differences across populations and in separate age classes revealed evidence of increasing genetic structure among younger age classes across the landscape. In a long-lived species with overlapping generations, it takes a long time to develop genetic substructure even when there are substantial obstacles to migration. Thus, in these recently fragmented populations, inbreeding (and the loss of heterozygosity) may be less of an immediate concern than demography (the loss of adults due to illegal hunting).