Population structure, phylogeography, and genetic diversity of the common bottlenose dolphin in the tropical and subtropical southwestern Atlantic Ocean

We assessed the level of genetic variability and population structure of the common bottlenose dolphin (Tursiops truncatus) in the tropical and subtropical portions of the southwestern Atlantic Ocean and compared the results with previous morphological findings. We analyzed 109 samples of common bottlenose dolphins that were sequenced for control region mtDNA and genotyped for seven polymorphic microsatellite loci. The results suggested that the species in this region can be separated in two major biological units, northern and southern, with an area of parapatry at southern Brazil. The northern unit seems to occur in a wide range of depths, including offshore waters, is consistent with the canonical morphology of T. truncatus, and can be divided into three management units: 1) Saint Paul's Rocks, 2) north and northeast of Brazil, and 3) Campos and Santos Basins (that extend at least to southernmost Brazil). The southern unit is coastal, occurring exclusively in very shallow waters (< 10 m) and estuaries, and is consistent with the previously described (putative) Tursiops gephyreus. Nevertheless, a formal decision on the taxonomic status of T. gephyreus should wait for a more geographically comprehensive and data-integrative study.