Evolutionary history of the porpoise family (Phocoenidae): A perspective from mitogenomes

The six species of porpoises inhabit the cold waters of the globe, displaying a textbook example of anti-tropical distribution in marine mammals. Nevertheless, the evolutionary history of the porpoises still remained poorly understood, but this knowledge is crucial to illuminate the conservation issues reported in these species (e.g. the nearly extinct vaquita, Yangzte finless porpoises; subspecies of harbour porpoises; poorly known spectacled and Burmeister porpoises). In this study, we reconstructed the evolutionary history of the porpoises in relation to past climatic changes. We used Next Generation Sequencing to assemble the mitochondrial genomes of 57 porpoises, resulting in a 16303 bps alignments. In contrast to previous beliefs, phylogenetic and population genetic analyses revealed that spectacled and Burmeister’s porpoises share a more recent common ancestor than with the vaquita. The vaquita would have split from the other during the Pliocene and then collapsed 3000 years ago. We also observed unreported subspecies level of divergence within the Pacific harbour porpoises similar to those reported in the North Atlantic, suggesting a richer evolutionary history than previously thought for this species. Our results provide a new perspective on the divergence, adaptation and speciation processes involved in the diversification of the porpoises.