Eastern tarsiers (Tarsius tarsier complex) are small nocturnal primates endemic to Sulawesi Island and small adjacent islands of Indonesia. In 2004, the hybrid biogeography hypothesis predicted this species complex might contain 16 or more taxa, each corresponding to a region of endemism, based on: 1) geological evidence of the development of the archipelago, 2) biological evidence in the form of concordant distributions of monkeys and toads, and 3) the distribution of tarsier acoustic groups. Since then, 11 tarsier species have been recognized, potentially leaving more to be described. Efforts to identify these cryptic species are urgently needed so that habitat conversion, pet trade, and cultural activities will not render some species extinct before they are recognized. We gathered data to test the hypothesis of cryptic tarsier species on three volcanic islands in Bunaken National Park, North Sulawesi, namely Bunaken, Manadotua, and Mantehage, during May-August 2018. We sequenced individuals at 5 nuclear genes (ABCA1, ADORA3, AXIN1, RAG, and TTR) and made comparisons to existing genotypes at 14 mainland sites. Bayesian phylogenetic analyses revealed that island populations are genetically identical in all 5 genes, and formed a clade separated from the mainland ones. The eastern tarsiers first diverged from the western tarsiers approximately 2.5 MYA. The three island populations diverged from mainland tarsiers approximately 2,000–150,000 YA, due to either human activities or natural rafting. This study provides information for tarsier conservation, advances the understanding of biogeography of Sulawesi, and contributes to Indonesian awareness of biodiversity. Further quantitative genetics research on tarsiers, especially the island populations, will offer significant insights to establish more efficient and strategic tarsier conservation actions.
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