Different evolutionary histories in two sympatric limpets of the genus Nacella (Patellogastropoda): inference of historical and contemporary processes underlying their intraspecific genetic patterns

DE ARANZAMENDI MC; BASTIDA RO; GARDENAL CN

Montreal

Conferencia; From Knowledge to Action - IPY2012 Montreal; 2012

The limpets of the genus Nacella are distributed in Antarctic and Subantarctic waters, including the Magellanic Province at the southern tip of South America that extends along both the Atlantic coast of Argentina and Pacific coast of Chile. Nacella species inhabiting the Magellanic Province are a suitable model to explore the impact of historical events in shaping population structure in marine coastal invertebrates with larval development and low mobile adults, since this area has been influenced by glacial processes and interglacial intervals during the last 800,000 years. The aim of this work was to study the phylogeographic patterns in two closely related limpet species, Nacella magellanica and Nacella deaurata, along the South-western Atlantic coast. Specifically, we used these data to infer the contribution of historical and contemporary processes to shape the genetic structure of Nacella species. Since Nacella magellanica and Nacella deaurata present overlapping geographical distribution in an area highly affected by recurrent growth and retreat of Pleistocene glaciers, their phylogeographic patterns should show signals of genetic bottlenecks and subsequent postglacial expansions. Regarding contemporary processes, marine currents plus pelagic larval duration could maintain low levels of genetic subdivision among populations. Our second objective was to determine whether gene flow has been occurring between these limpet species after their divergence. To fulfill these objectives, we utilized a partial sequence of the mitochondrial cytochrome oxidase I gene (COI) as molecular marker. Results indicate different evolutionary histories in the two species. A recent geographic and demographic expansion ~11,000 years ago, with absence of current genetic structuring, is proposed for Nacella magellanica. In contrast, the phylogeographic pattern showed noticeable phylogenetic and geographic discontinuities in Nacella deaurata; slow continuous population size growth with current low levels of gene flow among its populations was also observed, indicating demographic equilibrium. The presence of one shared haplotype in the COI sequence analyses between Nacella magellanica and Nacella deaurata is consistent with the recent estimated radiation for the Magellanic species. The presence of incomplete lineage sorting would be the most suitable explanation for the genetic similarity between these recognized species of Nacella, since the estimation of their separation indicates that these species diverged very recently (between 162,769 and 442,153 years ago), during the Pleistocene, with very little or none gene flow occurring after their splitting. This geological epoch has been characterized by repeated glaciations accompanying climatic change, which affected South of Patagonia and Tierra del Fuego. The presence of multiple refugia along the Magellanic Province during the last glacial cycles may have allowed the survival of these limpets during repeated advances and retreats of the ice. These contrasting historic patterns could be related to distinctive responses to climate changes associated with Pleistocene glaciations, as a result of differences in their ecological traits.