New molecular markers for revealing the population structure of Chthamalus stellatus in the Mediterranean and the eastern Atlantic

This study addressed the hypothesis that the lack of genetic variation among populations of the barnacle Chthamalus stellatus, detected in previous phylogeographic studies, is due to the limitations of the selected markers. We developed novel markers for this species based on 2 mitochondrial sequences, i.e. a 640 bp fragment of NADH dehydrogenase subunit 2 (ND-2) and a 228 bp fragment of the control region (CR). We found that ND-2 is highly conserved in the chthamalids and thus is not suitable for phylogenetic analyses of this group. In the CR, 204 haplotypes were recognized, of which 182 were singletons. The range of pairwise differences between populations was 6.7 to 8.9. The high variance (85 to 89%) of the CR occurs within populations, leaving only 11 to 15% of the variation between populations. The model separating the Azores population from the other Atlantic populations, and the Mediterranean population from the Atlantic populations, gave the highest variation among groups. But due to the limitations of the markers used, the hypothesis that there is genetic variation among populations of C. stellatus needs further support. The low variability of the ND-2 gene and the high variability of the CR limit the validity separation of populations of C. stellatus. The phylogeographical study of chthamalids requires development of different genetic markers; it is possible that the use of microsatellites could fulfill these requirements and reveal significant differences among populations.