Different evolutionary histories in two sympatric limpets of the genus Nacella (Patellogastropoda) in the South-western Atlantic coast

The phylogeography of two sympatric Magellanic limpets of the genus Nacella was studied. The historical and contemporary processes underlying their intraspecific patterns in Argentina were inferred using the mitochondrial cytochrome oxidase I gene. 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 beginning of divergence between these closely related limpets was estimated at about 270,000 years ago with very little or none gene flow occurring after their splitting. 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.