Impact of geographic isolation on the genetic diversity of diademed sifakas (Propithecus diadema) and black-and-white ruffed lemurs (Varecia variegata) in eastern Madagascar

Isolation of forest fragments surrounded by urban and agricultural land prevents gene flow between arboreal species that cannot migrate between forest patches, ultimately leading to the loss of genetic diversity necessary for their long-term survival. To evaluate the effect of geographic isolation on two Critically Endangered lemur species in eastern Madagascar, we characterized and compared the genetic diversity of diademed sifakas ( P. diadema ) and black-and-white ruffed lemurs ( V. variegata ) in Betampona Strict Nature Reserve and Vohibe Forest using mitochondrial haplotypes and multi-locus autosomal microsatellite genotypes. Betampona is a fragment completely detached from the northeast of the Ankeniheny-Zahamena forest corridor (CAZ) around 60 years ago, and Vohibe is part of a larger fragment at the southern-most end of the CAZ. We predicted lower genetic diversity in Betampona due to its long-term isolation. To test this prediction, at each site, we analyzed fecal samples from three groups of P. diadema (Betampona N=6; Vohibe N=12) and three subgroups of V. variegata (Betampona N=12; Vohibe N=11). We observed a single mtDNA haplotype, lower allelic richness, and lower variability among genotypes for P. diadema but higher mtDNA haplotype diversity and allelic richness for V. variegata in Betampona versus Vohibe, suggesting a contrasting effect of Betampona’s geographic isolation on each species. In fact, genetic diversity of V. variegata in Betampona was higher than that reported at other sites across the species range. This genetic characterization can inform current and future conservation actions in Betampona and Vohibe, especially those aimed at maintaining genetically viable populations.