Evolutionary animation in the tremendously speciational skates (Elasmobranchii, Rajoidea)

In spite of high level of morphological, reproductive and ecological conservativism, skates (suborder Rajoidea) are a group of highly diverse cartilaginous fish, whose evolution and diversification started since Late Cretaceous likely driven by Gondwanaland breakup and continental plate migration. More than 200 nominal species are presently inventoried being distributed over all Oceans, latitudes and marine ecosystems. Since speciation has been tremendous in such ancient monophyletic group, we have reconstructed evolutionary patterns and processes in the biogeographically monophyletic Eastern Atlantic skate faunas at multiple taxonomic levels by analyzing population genetic structure, phylogeographical and phylogenetic relationships in key-role taxa and clades. Variation patterns of genomic, nuclear and mitochondrial loci in Raja species revealed that geographical subpopulation structuring and cryptic speciation strongly contributed to the evolution of taxa diversity during Pliocene-Pleistocene. Comparative analysis of mitochondrial phylogenies and zoogeography of species belonging to the genera Raja, Leucoraja, Rajella, Dipturus, Amblyraja and Rostroraja revealed that present fauna diversity evolved since Early Miocene. The allopatric speciation and accumulation of genome divergence over time seem to be the predominant processes in shaping species diversity in these clades. However, the occurrence of relatively recent sympatric sister species indicate that also the rapid onset of highly efficient reproductive barriers could be relevant for cladogenesis in such group. Conspecific subpopulations geographically structured, adjacent sibling species and allopatric divergent sister species appeared rather like evolutionary animation of such still intriguing fish clade.