Taxonomic discrimination of Raja polystigma and Raja montagui in the Mediterranean Sea based on the comparative analysis of morphometric and genetic markers

In the last years many studies based only on morphological features revealed a diffuse uncertainty in the taxonomic discrimination between individuals of Raja montagui (distributed in the NE Atlantic and Mediterranean) and Raja polystigma (endemic of the Mediterranean). This could be related to the inappropriateness of the morphological characters reported in the identification keys used to distinct the two species. The achievement of reliable tools for the identification of the two species will be useful for improving life-history traits and species assessment. The nucleotide variation of the species-specific gene marker 16S rDNA was analysed for 115 individuals collected in NE Atlantic and in different areas of the Mediterranean basin (Adriatic Sea, Thyrrenian Sea, Sardinian Channel, Sicily Channel and Algeria) and morphologically recognized as Raja montagui and R. polystigma. 79 individuals were identified bearing the R. polystigma haplotype and 9 individuals bearing the R. montagui haplotype. A second R. polystigma haplotype was found in 27 individuals from the Thyrrenian Sea. Among the 75 individuals collected in the Italian Seas, none showed a 16S R. montagui haplotype. Many incongruence between morphological appearance and mitochondrial haplotypes were observed in these specimens. Among the 16S-genotyped individuals, dorsal and ventral digital pictures were taken on about 60 individuals. The software used for the shape analysis allowed easy measurement and included advanced graphical capabilities for the visualization of morphometric data and results. 14 and 22 relevant landmarks were chosen, respectively on the dorsal and ventral side of the ray. 33 distances and 5 angles were calculated for each sample. Moreover, the main dorsal spines row and the upper and lower teeth rows were measured. No clustering of individuals according to species boundaries was observed. These preliminary results seem to indicate that R. montagui is not probably present in the Italian seas and, within the Mediterranean, it is present along the Algerian coasts.