Rough-toothed dolphins have a worldwide circumtropical to warm-temperate distribution in open-ocean and slope waters. Despite this large geographic distribution, the global phylogeography and the divergence between the Pacific and Atlantic Oceans has not been well described. Given their circumtropical distribution, continental landmasses have acted as barriers to dispersal. Therefore, we investigated the potential for ocean basins to lead to phylogeographic structure, and further evaluated population level structure among oceans, using mitogenomes (n=24), the mtDNA control region (n=351), and six nuclear introns (n=35) for representative samples from the Pacific, Indian and Atlantic Oceans. Phylogenetic analyses of the mitogenome revealed four clades including an Atlantic clade sister to a larger cosmopolitan clade containing individuals from all three oceans. Using the first mitogenome substitution rate estimated specifically for rough-toothed dolphins, we dated the divergence time between the endemic Atlantic clade and the cosmopolitan clade to one million years ago. Although the phylogenetic reconstruction did not reflect reciprocal monophyly by ocean basin, the mitogenome population level analyses revealed significant genetic differentiation among all oceans (global ΦST = 0.368, p < 0 .001). Nuclear introns indicate significant differentiation between the Atlantic and the other two oceans (FST = 0.150, p < 0 .001 Pacific and FST = 0.135, p < 0 .001 Indian), but no significant differentiation was found between the Pacific and Indian Oceans (FST = 0.0091, p=0.441). Within each ocean, local isolated populations were also documented. Overall, these results suggest rough-toothed dolphins have maintained low levels of gene flow across the Indo-Pacific on an evolutionary time scale, and that dolphins in the Atlantic have been isolated sufficiently from conspecifics in the other oceans to be on an independent evolutionary trajectory.
Albertson, R., A. Alexander, K. Martien, R.W. Baird, M. Oremus, S. Caballero-Gaitan, M. Poole, R. Brownell, D. Duffield, C. S. Baker. 2017. Worldwide Phylogeography of the Rough-Toothed Dolphin (Steno bredanensis) Described Using Mitogenomes and Nuclear Introns. Abstract of the 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.