Evolutionary history of the four-spotted megrim (Lepidorhombus boscii) and speciation time within the genus based on mitochondrial genes analysis

The evolutionary history and geographic distribution of North-Atlantic and Mediterranean marine taxa has been largely affected by past geological and climatic events, like the Messinian salinity crisis, the opening of the Strait of Gibraltar and the Quaternary glacial cycles. The four-spotted megrim Lepidorhombus boscii is a demersal flatfish of the family Scophthalmidae (Pleuronectiformes), distributed in the Northeast Atlantic and the Mediterranean Sea. During its larval development it is planktonic, being passively drifted by marine currents, while adults are more or less sedentary living near the sea bottom. In order to investigate whether past geological and climatic events have influenced the evolutionary and demographic history of L. boscii, we analyzed a fragment of the highly variable mitochondrial control region in 163 individuals from different North-Atlantic areas and from the Mediterranean Sea. Contemporary processes of moderate gene flow, partially restricted by isolation by distance, as well as recent paleoecological events like the last Pleistocene glaciation, seem to play key roles in shaping the current phylogeographic pattern of the four-spotted megrim. On the other hand, we also analyzed 94 individuals from different North-Atlantic areas of its congeneric species L. whiffiagonis in order to compare genetic variation patterns within this genus. Finally, we used a fragment of the protein-coding mitochondrial gene cytochrome c oxidase I to estimate the time of speciation in megrims. Results suggest that divergence between the two species likely took place 5.3 MYA, which can be correlated with the end of the Messinian salinity crisis.