Historical dimensions of population structure in a continuously distributed marine species: The case of the endemic Chilean dolphin.

The complementarity of historical and contemporary processes contributes to understanding the genetic structure of continuously distributed marine species with high dispersal capabilities. Cephalorhynchus eutropia, has a continuous coastal distribution with strong genetic differentiation identified by nuclear DNA markers. We explored the historical dimension of this genetic differentiation between northern and southern populations to evaluate phylogeographic structure. Additionally, we conducted mtDNA and microsatellite analyses to detect past and recent demographic changes. The southern population was characterized by lower genetic diversity with a signal of population expansion, likely associated with ice retreat and habitat extension after the Last Glacial Maximum (LGM). In contrast, structure within the northern population was more consistent with stable historical population size. Approximate Bayesian Computation analyses suggested that during the LGM, C. eutropia persisted in the northern area; while the south was colonized by dispersal ~11,000 years ago followed by population expansion. This study shows that Chilean dolphin population structure is consistent with predictions from the Expansion-Contraction biogeographic model, with a poleward post-glacial shift revealed in current genetic structure. The results also confirm the validity of the population units previously identified, demonstrating their historical origin and highlighting the utility of integrating genetic markers with different temporal scale resolutions.

Captive-born intergeneric hybrid of a Guiana and bottlenose dolphin: Sotalia guianensis x Tursiops truncatus.

Bottlenose dolphins (Tursiops truncatus) and Guiana dolphin (Sotalia guianensis) live in sympatry along the Caribbean Coast of Central and South America and social interactions between these species have been described in the Caribbean Coast of Costa Rica, including sexual encounters. Here we examine and document the only known hybridization event between a male Guiana dolphin and a female bottlenose dolphin, in captivity at Oceanario Islas del Rosario (Colombian Caribbean), using photographic and genetic evidence from mitochondrial DNA markers and nuclear autosomal introns.