PNNL

Abstract

Rough-toothed dolphins have a global tropical and subtropical distribution. Previous genetic studies have found significant genetic differentiation among island groups suggesting strong population structure, possibly due to social or demographic factors. As part of a conservation effort for this little studied species, we used mtDNA control region (n=350), mitogenomes (n=20) and six nuclear introns (n=35) in order to assess multiple lines of evidence critical to the process of taxonomic evaluation. We examined the null hypothesis that rough-toothed dolphins are one panmictic species using samples from the Pacific, Indian and Atlantic Oceans. MtDNA phylogenetic analyses indicated three migration events and a private Atlantic clade sister to a larger cosmopolitan clade containing individuals from all three oceans. We dated the split between the Atlantic clade and the cosmopolitan clade to 0.890 MYA and determined that West Atlantic rough-toothed dolphins can be assigned to their ocean basin with 97% accuracy. MtDNA population level analyses revealed significant genetic differentiation among five biogeographic regions, while the nuclear introns detected significant differentiation between only the Atlantic and other regions. These results suggest rough-toothed dolphins in the Atlantic have been isolated for a sufficiently long time from the other regions warranting the designation as a separate subspecies.