Phylogenetic analysis of mtDNA sequences suggests revision of humpback dolphin (Sousa spp.) taxonomy is needed

Humpback dolphins (Sousa spp.) have a wide distribution in the tropical Atlantic and Indo-Pacific Oceans and a confused taxonomy. Morphological assessments suggest three species groupings-Sousa teuszii (eastern Atlantic), Sousa plumbea (western Indo-Pacific), and Sousa chinensis (eastern Indo-Pacific)-but most taxonomies recognise only two species-S. chinensis (Indo-Pacific), and S. teuszii (Atlantic). To investigate phylogenetic relationships, mitochondrial DNA control region sequences (338 base pairs) from 72 Sousa representing three populations in the Indo-Pacific (South Africa: S. plumbea, n=23; China: S. chinensis, n=19; and Australia: S. chinensis, n=28), and S. teuszii in the Atlantic (Mauritania, n=2) were generated. All three Indo-Pacific populations formed robust, monophyletic clades with high bootstrap (BS) and Bayesian posterior probability (BPP) scores. Surprisingly, humpback dolphins from South Africa and China formed a strongly-supported clade with the Atlantic S. teuszii (BS 63%, BPP 0.92) to the exclusion of animals from Australia. Genetic divergence between animals from China and Australia (D-A = 8.4% +/- 2.47%) was greater than between China and South Africa (D-A = 5.1% +/- 1.80%). These results strongly suggest that Australian humpback dolphins are not S. chinensis but may represent a distinct species in their own right.