Concerted genetic, morphological and ecological diversification in Nacella limpets in the Magellanic Province

Abstract Common inhabitants of Antarctic and Subantarctic rocky shores, the limpet genusNacella, includes 15 nominal species distributed in different provinces of the SouthernOcean. The Magellanic Province represents the area with the highest diversity of thegenus. Phylogenetic reconstructions showed an absence of reciprocal monophyly andhigh levels of genetic identity among nominal species in this Province and thereforeimply a recent diversification in southern South America. Because most of these taxacoexist along their distribution range with clear differences in their habitat preferences,Nacella is a suitable model to explore diversification mechanisms in an area highlyaffected by recurrent Pleistocene continental ice cap advances and retreats. Here, wepresent genetic and morphological comparisons among sympatric Magellanic nominalspecies of Nacella. We amplified a fragment of the COI gene for 208 individualsbelonging to seven sympatric nominal species and performed geometric morphometricanalyses of their shells. We detected a complete congruence between genetic andmorphologicalresults,leadingustosuggestfourgroupsofNacellaamongsevenanalysednominal species. Congruently, each of these groups was related to different habitatpreferences such as bathymetric range and substrate type. A plausible explanation forthese results includes an ecologically based allopatric speciation process in Nacella.Major climatic changes during the Plio-Pleistocene glacial cycles may have enhanceddifferentiation processes. Finally, our results indicate that the systematics of the grouprequires a deep revision to re-evaluate the taxonomy of Nacella and to further understandthe Pleistocene legacy of the glacial cycles in the southern tip of South America.Keywords: adaptive radiation, ecological speciation, Nacella, Patagonia, Patellogastropoda,Southern OceanReceived 5 November 2010; revision received 27 January 2011; accepted 9 February 2011