New insights on population genetic structure of Delphinus delphis from the northeast Atlantic and phylogenetic relationships within the genus inferred from two mitochondrial markers

The taxonomic status of common dolphins (Delphinus sp.) remains controversial despite the increased number of studies focusing on its populations. Two species are presently recognized, Delphinus delphis and D. capensis. Apart from a phylogeographic study of the genus Delphinus, genetic studies focusing specifically in the northeast (NE) Atlantic remain scarce. Following ecological and morphological evidence for the existence of different common dolphin morphotypes in the Portuguese coast, we examined the population structure of D. delphis from the NE Atlantic by comparing DNA sequences from two mitochondrial regions (control region and cytochrome b gene). Additionally, we compared the sequences obtained with existing sequences of D. delphis from the Azores, Black Sea, Canary Islands, Pacific Ocean, D. capensis and also two closely related delphinid species (Stenella coeruleoalba and Tursiops truncatus). In the analysis of the NE Atlantic populations, we found evidence for the existence of some level of genetic differentiation. In the broader phylogenetic analysis, D. delphis and D. capensis did not show reciprocal monophyly and we found a group of highly divergent individuals. We discuss the possibility for the existence of two divergent lineages that have evolved independently, a separate subspecies or events of introgressive hybridization. These findings could have important implications on a taxonomic level, although further investigation based on a larger geographical scale and on nuclear loci information will certainly elucidate the origin of these highly divergent individuals.