Molecular taxonomy and population genetic processes in the genus Sousa

The hump-backed dolphin, Genus Sousa, is a small inshore cetacean in the sub-family Delphininae, often associated with rivers and estuaries. It is found in the Western Pacific and Indian Oceans and West Africa. The species taxonomy is unclear, with two to five species presently identified. This study investigates taxonomy within the Genus and population genetic processes, assaying sequences variation of the mitochondrial control region and nuclear microsatellite loci. A total of 81 individuals from three localities along its geographical range was analyzed (Honk Kong (19), Natal (23), Eastern Australia (23),Northern Australia (1), Western Australia (2), Mauritania (2) and Somalia (1)), incorporating a data set from closely related species, Tursiops aduncus, Tursiops truncatus, and Delphinus delphis. The pattern of mtDNA and allele size frequency distribution provided evidence of strong female philopatry, assuming male-biased gene flow, even though restricted to the localities studied, as the key factor in maintaining genetic diversity within populations. Such restriction in the gene flow at both male and female level shows consistency with the morphological differences identified among localities. An overall estimate of low genetic diversity at each locality was found at both mtDNA and nuclear microsatellite analysis due to strong genetic drift, which extent strongly correlates to the presence of small effective population size at each locality. To conclude the analysis of both mitochondrial and nuclear DNA revealed levels of divergence of similar magnitude to that between related known species, strongly indicating levels of species divergence among the three localities. The molecular taxonomy generated in this study proposes to divide the Genus into at least three different species: Australia, Honk Kong, and Natal