Another piece of the evolutionary history of Atlantic skates (Chondrichthyes, Rajiformes ): integrating DNA barcoding approach and phylogenetic inferences

Conservation and long-term management plans of marine species need to be conceived upon a universally recognised key-feature: species identity. This important assignment resulted particularly arduous among skates (order Rajiformes), in which the phenotypic similarity between some taxa and the individual variability in others, entangled accurate species identification. This study confirms the power of DNA barcoding for the discrimination between skate species across the Atlantic Ocean and for its use as effective tool to minimize the risk of species misidentification and to elucidate species boundaries. In this perspective, this work compiles and establish a new fully available and well-curated barcode library, the ELASMO-ATL project, which gathered biological and molecular information of 432 skate specimens and covered coastal waters of four FAO Major Fishing Areas (27, 34, 47, 41) of the Atlantic Ocean. The evolutionary histories of 34 skate species were estimated with two concatenated mitochondrial markers (COI and NADH2) through Bayesian and species level phylogeny analyses. It was possible to discover a new evolutionary lineage within the genus Raja in the southern-most part of its distribution area and to enable deepening the relationship between South-African endemic species of Rajella. Once again, Western South African coasts and oceanographic fronts may play a fundamental role among skates’ speciation events in which the paleoclimatic and paleogeographic history joined to hydrography events could have contributed to the formation of refugial areas, characterised by geographical isolation. Subsequent contact zones in these areas between Senegal and Angola seems to constitute a continuum/cline of genetic change among some Raja species. These data successfully resolved many taxonomic ambiguities and demonstrated a highly cohesive monophyletic clustering among the order laying the foundations for further inference of evolutionary patterns suitable for addressing management and conservation issue.