Abstract
The occurrence of hybridisation between limpet species of the genus Patella has always been a contentious issue. Although a previous allozyme study reported high differentiation and no hybridisation between Patella vulgata Linnaeus, 1758, Patella depressa Pennant, 1777 and Patella ulyssiponensis Gmelin, 1791 along English shores, the recent finding of an mtDNA haplotype of P. depressa in a P. vulgata individual raised new doubts on this issue. To further study the possibility of hybridisation between limpet species and their level of genetic differentiation, ten allozyme loci were screened using starch gel electrophoresis for P. ulyssiponensis, P. depressa, P. vulgata and Patella rustica Linnaeus, 1758, from the Atlantic coast of the Iberian Peninsula. Our results show high differentiation between species, which could be clearly separated into different clusters with a Bayesian clustering algorithm. No significant signs of hybridisation were detected between any of the four species. Thus, the hypothesis of hybridisation between P. vulgata and P. depressa across their sympatric distribution is not supported. Two sympatric clusters were recovered within P. vulgata that could be related to Hardy-Weinberg disequilibrium found in locus MPI. Finally, due to the high level of intraspecific variability, the studied loci are interesting tools for the analysis of population structure and stock identification.
Highlights
The genus Patella belongs to the order Patellogastropoda and is distributed across rocky shores of the northeast Atlantic and the Mediterranean and Black Seas
A recent study based on two mitochondrial genes (Koufopanou et al, 1999) revealed a haplotype in Patella vulgata Linnaeus, 1758 very similar to those found in Patella depressa Pennant, 1777
This haplotype was later confirmed to belong to the clade of P. depressa and to be very distinct from those found in P. vulgata (Sá-Pinto et al, 2005)
Summary
The genus Patella belongs to the order Patellogastropoda and is distributed across rocky shores of the northeast Atlantic and the Mediterranean and Black Seas (see review in Ridgway et al, 1998). Characters such as the colour of the foot and paleal tentacles, the colour and shape of the internal and external parts of the shell and the radular teeth morphology (Fischer-Piette and Gaillard, 1959) Most of these characters show high morphological plasticity and are influenced by environmental conditions (Branch, 1981), leading to an overlap of states between different species (see for example Mauro et al, 2003). A recent study based on two mitochondrial genes (Koufopanou et al, 1999) revealed a haplotype in Patella vulgata Linnaeus, 1758 very similar to those found in Patella depressa Pennant, 1777 This haplotype was later confirmed to belong to the clade of P. depressa and to be very distinct from those found in P. vulgata (Sá-Pinto et al, 2005). No signs of introgression between the two species were found by Sá-Pinto et al (2005), the low sample size prevents a clear picture from being drawn from this study and highlights the need for further studies involving nuclear markers and larger sample sizes
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