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

Abstract

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.

From Settlers to Subspecies: Genetic Differentiation in Commerson’s Dolphins Between South America and the Kerguelen Islands

“…Chilean dolphins inhabit the coastal waters of central and southern Chile, from Valparaíso to Isla Navarino (Goodall, 1994) and a few have also been documented on the Atlantic coast at Puerto Deseado, Argentina (Morgenthaler et al, 2014). Their current genetic structure along the Chilean coastline is consistent with predictions from the Expansion-Contraction biogeographic model with a poleward post-glacial shift (Pérez-Alvarez et al, 2016).…”

Global phylogeography and genetic diversity of the long-finned pilot whale Globicephala melas, with new data from the southeastern Pacific

“…During this period, a 6-10 °C cooling occurred in superficial waters of southeast New Zealand, the strongest temperature drop reported in this area of the southwestern Pacific 47 . Such changes in environmental conditions, probably associated to a shift in the distribution Table 1. of marine biota, may have provoked a typical population contraction-expansion in the long-finned pilot whale population in this area, as described for cold-temperate and polar marine species 48 , including cetaceans 49,50 .…”

A Genetic Perspective on Cetacean Evolution

“…Population genetic structure and dispersal are the result of contemporary and historical processes. For instance, glacial oscillations during the Pleistocene [2.5 Mya to 11.7 kya (thousand years ago)] had a large influence on the distribution, genetic structure, and connectivity of cetacean species and populations from both hemispheres (e.g., Jackson et al 2014, Pérez-Alvarez et al 2016. During glaciations, some cetacean populations became contracted and isolated, reducing gene flow and promoting genetic differentiation.…”