First assessment of the genetic structure of deepwater blackmouth catshark (G. melastomus Rafinesque, 1810) in Atlantic and Mediterranean populations

The worldwide abundance of Galeus melastomus in the biological composition of fishery bycatch led to consider this species as a key-taxon for understanding the mysterious biology and ecology of sharks living in deep ecosystems. With the present work, we aim to unravel the population structure of the blackmouth catshark in the Mediterranean Sea and adjacent North-Eastern Atlantic with the use of nuclear molecular markers (simple sequence repeats, SSRs) and compare our results with recent findings based on mitochondrial DNA supporting total panmixia in the species. Given the absence of species-specific microsatellite markers we attempted the cross-amplification of a panel of 129 SSRs developed for Centroselachus crepidater, Galeorhinus galeus, Hexanchus griseus, Mustelus antarcticus, M. canis, M. henlei, M. mustelus, Negaprion brevirostris, Scyliorhinus canicula, Squalus acanthias and S. mitsukurii on blackmouth catsharks collected during scientific surveys undertaken in different years. The rationale of the chosen methodology was based on the calculation of genetic distances between NADH2 sequences (1044bp long) derived from 595 species of elasmobranchs. Our strategy focused on testing first SSRs markers developed on closely-related species. Then, we assessed highly polymorphic markers developed on non-closely-related species. After a pilot gradient amplification on few individuals from three different geographic macro-areas, we screened a total of 24 samples at the established conditions. To date, 16 microsatellite loci have been classified as potential candidates for the succesful cross-amplification on Atlantic and Mediterranean samples of G. melastomus. These candidate loci will be applied in the population genetic analysis delineated in the Atlantic Ocean (two sites) and in the Mediterranean Sea (five sites). Hopefully, the higher resolution power of the markers chosen for this study will be able to disclose any signal of genetic structure of the blackmouth catsharks and will contribute to improve the knowledge on deep-sharks.