Data from: Phylogeographic analysis of Ligia oceanica (Crustacea: Isopoda) reveals two deep divergent mitochondrial lineages

Isopods of the species Ligia oceanica are typical inhabitants of the rocky intertidal of the northern European coastline. The aim of this study was to assess the genetic structure of this species using mitochondrial and nuclear sequence data. We analysed partial mitochondrial cytochrome c oxidase subunit I (CO1) and 16S rDNA sequence data of 161 specimens collected from 10 sites ranging from Spain to Norway. For selected specimens, we also sequenced the hypervariable V7 expansion segment of the nuclear 18S rRNA gene as supplementary marker. Furthermore, we studied the infection rate of all analysed specimens by the α-proteobacterium Wolbachia. Our analyses revealed two deeply diverged mitochondrial lineages for Ligia oceanica that likely diverged in the late Pliocene to mid Pleistocene. One lineage comprises specimens from northern populations (“lineage N”) and one primarily those from France and Spain (“lineage S”). Distribution patterns of the haplotypes and the genetic distances between both lineages revealed two populations that diverged before the last glacial maximum. Given that we found no homogenization of mitochondrial haplotypes, our present results also reject any influence of Wolbachia on the observed mitochondrial DNA variability.