The common bottlenose dolphin (Tursiops truncatus) ecotypes of the western North Atlantic revisited: an integrative taxonomic investigation supports the presence of distinct species

Integrative taxonomy can help us to gain a better understanding of the degree of evolutionary divergence between taxa. In the western North Atlantic (wNA), two ecotypes (coastal and offshore) of common bottlenose dolphin, Tursiops truncatus, exhibit some external morphological differences, and previous genetic findings suggested that they could be different species. However, their taxonomy remains unsettled. Using an integrative approach comparing traditional and geometric morphometrics, mitochondrial and nuclear DNA, we evaluated evolutionary relationships between these ecotypes. We observed congruence among these lines of evidence, strongly indicating that the wNA ecotypes are following distinct evolutionary trajectories. Based on mitochondrial DNA analyses, we detected significant divergence (Nei's d(A) = 0.027), unshared haplotypes and one fixed difference leading to complete diagnosability (percentage diagnosable = 100%) of the wNA coastal ecotype. We found morphological diagnosability and negligible nuclear gene flow between the wNA ecotypes. Integration of these multiple lines of evidence revealed that the wNA coastal ecotype is an independent evolutionary unit, appearing to be more closely related to coastal dolphins in the Gulf of Mexico and Caribbean Sea than to their parapatric offshore neighbours, while the offshore dolphins form a relatively cohesive worldwide unit, T. truncatus. We propose that this coastal ecotype is recognized as a distinct species, resurrecting the name Tursiops erebennus.