Population genetics of species on the genera Tursiops and Delphinus within the Gulf of California and along the western coast of Baja California.

Abstract

This present study investigated the evolution of population genetic structure of two closely related cetacean species, bottlenose (Tursiops truncatus) and common dolphins (Delphinus spp.) within the Gulf of California (GC) and along the West Coast of Baja California. In this study, we found evidence of strong genetic differentiation in both bottlenose and common dolphin populations in the absence of physical barriers. The comparison of the patterns of population genetic differentiation found here for bottlenose and common dolphins supports the hypothesis of local habitat dependence and resource specialization at both the population and putative species level. Fine-geographic scale structure was detected in coastal bottlenose dolphins, which seemed to be strongly associated to the biogeographic subdivision of the Gulf of California and western coast of Baja California. This result suggests that gene flow among bottlenose dolphin coastal populations might be restricted by local dependence on diverse ecological conditions. In contrast, the long-beaked common dolphin genetic structure did not reflect the habitat heterogeneity of the region to the same extent. The difference in foraging specialization between coastal and offshore populations of both bottlenose and common dolphins is reflected in the pattern of genetic structure observed at a broader geographic scale.
Overall, the results support the hypothesis that local habitat dependence promotes population differentiation in the absence of physical boundaries to dispersal in these highly mobile species. This study provides an unusual insight into the conditions that lead to incipient speciation in these groups. Divergence among common dolphin populations appears to be associated with changes in the paleoceanographic conditions of the region to the extent that reciprocal monophyly between the sympatric D. delphis and D. capensis forms has evolved within the Holocene timeframe.