The cradle of diversity: Central Atlantic Ocean hides a mosaic of skate species (Rajiformes)

Skates (Rajiformes) represent one of the most intriguing cases of high species richness coupled with extremely conservative morphological and ecological traits. Small differences are described within and between species and increasing cases of cryptic speciation have been recorded among sister and non-sister taxa. More interestingly, this condition has been frequently observed in Central Atlantic Ocean (CAO), along the coasts of Western Africa, between Angola and Senegal, where oceanographic heterogeneities such as current systems, may play a key role for ecological speciation in skates. The use of multiple mtDNA loci and its integration with nuDNA microsatellite has been successfully applied to estimate the genetic variation in skate species inhabiting the CAO. Phylogenetic reconstructions, phylogeographic patterns and genetic connectivity estimates were applied to test the hypothesis that restricted gene flow and genetic divergence within Raja species reflect known climate and bio-oceanographic discontinuities. The widely distributed Raja miraletus species complex counts five deeply distinct lineages three of which co-occur in CAO: the Angolan Raja cf. miraletus, the Senegalese and sympatric R. parva and Raja cf. miraletus. In addition, an ancient, hidden lineage nesting in the clade Raja straeleni/R. clavata/R. maderensis was identified in Angola. The complexity of oceanographic system acting in the CAO (i.e., the Benguela Current region and the intertropical Canary current inflowing from the northeast) may have influenced the diversification of the Angolan and Senegalese taxa, boosting the biodiversity of the area, in an unprecedented anthology of species-specific evolutionary histories.