The eventful history of a "living fossil" - phylogeny and phylogeography of Sulawesi tarsiers
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Abstract
In the 19th century, the British naturalist Alfred R. Wallace recognised the exceptional biogeography of the Malay Archipelago and the particularly interesting position of Sulawesi. Now, 150 years later, this region still casts its spell over scientists worldwide. Sulawesi represents the largest island belonging to Wallacea, a biogeographic transitional zone of Asian and Australian biota named after Wallace. Although having a rich fauna, only two primate taxa were able to colonize this island, macaques and tarsiers. The fossil record of tarsiers in Southeast Asia is assumed to go back to the Eocene epoch and also their arrival on Sulawesi clearly predates that of the macaque´s. Before Sulawesi took on its current shape and environmental conditions, tectonic processes and Pleistocene climate fluctuations formed today´s endemism patterns and thus also affected the diversification in tarsiers. However, even today, a well resolved phylogeny representing a wide range of Sulawesi tarsier taxa for concluding possible dispersal routes over the island is missing. Here a multifaceted investigation based on a comprehensive sample set (160 samples from 14 populations) and a variety of molecular tools (mitochondrial, Y-chromosomal, and autosomal DNA markers) complemented by acoustic data has been conducted to infer phylogenetic relationships among tarsier populations of different geographic origin. Species tree reconstructions derived from sequence data of five nuclear markers point to a common ancestor of Sulawesian tarsiers at approximately 20 MYA (95% confidence interval ranges from 13.71-28.15 MYA), going along with the split of crown tarsiers. The progenitor of Sulawesi tarsiers likely reached the island via dispersal and outlasted almost 10 millon years of the Neogene period on the palaeo-Sulawesi archipelago probably with limited expansion possibilities. Further speciation that separated two major lineages of Eastern tarsiers began around the Plio-Pleistocene border, ca. 2-2.5 MYA (95% confidence interval ranges from 1.34-3.54 MYA). Bayesian clustering applied on eight microsatellite loci partitioned populations into seven groups, whereby effects of male-mediated gene flow and isolation by distance biased the population structuring in some respects. Discordance between mtDNA and nuclear DNA strongly hint at female philopatry and male dispersal.