On the Phylogenetic History of the Sanje Mangabey (Cercocebus sanjei), Udzungwa Mountains, Tanzania

Abstract An accurate understanding of phylogeny, including intraspecific diversity, is key for defining conservation measures. The Sanje mangabey ( Cercocebus sanjei ) is an Endangered primate endemic to the Udzungwa Mountains in Tanzania that inhabits montane forest fragments and occurs in two populations—Mwanihana Forest and Uzungwa Scarp Nature Reserve—located 100 km apart. The phylogenetic position of the Sanje mangabey relative to other Cercocebus species remains unclear. We aimed to clarify the phylogeny of the Sanje mangabey and estimate its divergence time from other species. We reconstructed phylogenies using nuclear (CD4 and TSPY) and mitochondrial (COII and control region) sequences in noninvasive DNA sampled from both the populations (n = 88 sequences). We found that the Sanje mangabey grouped with the central/East African mangabeys ( C. galeritus , C. chrysogaster , and C. agilis ) and estimated that it diverged from the common ancestor ~2.34 million years ago (MYA; 95% Highest Probability Density (HPD) interval: 1.73–2.95 MYA). Results suggest that the two extant Sanje mangabey populations represent distinct lineages, diverging 0.77 MYA (95% HPD interval: 0.43–1.15 MYA). This divergence and isolation into two montane forest fragments may be attributed to increasing aridification in eastern Africa beginning ~2.6 MYA, the formation of physical barriers to dispersal and competition with other species. By confirming the evolutionary distinctiveness of the Sanje mangabey relative to other Cercocebus species, this study highlights the need for dedicated conservation management policies. Such policies should also consider the two populations as candidate evolutionary significant units. Further morphological, genetic, and behavioural studies are needed to assess the extent of reproductive isolation in Sanje mangabeys. Our study highlights the need to identify cryptic diversity within threatened species in order to improve their conservation.