I Like This New Me: Unravelling Population Structure of Mediterranean Electric Rays and Taxonomic Uncertainties within Torpediniformes

SIMPLE SUMMARY: Electric rays are currently poorly investigated; therefore, their biological status, species identification and distribution are often hard to assess. The present work, using mitochondrial sequence data, aimed to investigate (1) the genetic diversity of the three species of electric rays reported in the Mediterranean Sea (Torpedo torpedo, Torpedo marmorata and Tetronarce nobiliana); and (2) the possible occurrence of other hidden species in the area. Our results suggest that (1) the Sardinian seas (Western Mediterranean) host populations characterized by high levels of genetic diversity, significantly different from other areas located in the Eastern Mediterranean basin, deserving special attention; (2) only three species occur in the investigated area; (3) inaccuracies exist in the current taxonomy of the three investigated species, such as the possible occurrence of cryptic species outside the Mediterranean Sea, as well as in other genera/families of the order Torpediniformes. Future studies are needed to address these issues and inform effective conservation measures. ABSTRACT: The present study focused on the three species of electric rays known to occur in the Mediterranean Sea: Torpedo torpedo, Torpedo marmorata and Tetronarce nobiliana. Correct identification of specimens is needed to properly assess the impact of fisheries on populations and species. Unfortunately, torpedoes share high morphological similarities, boosting episodes of field misidentification. In this context, genetic data was used (1) to identify specimens caught during fishing operations, (2) to measure the diversity among and within these species, and (3) to shed light on the possible occurrence of additional hidden species in the investigated area. New and already published sequences of COI and NADH2 mitochondrial genes were analyzed, both at a small scale along the Sardinian coasts (Western Mediterranean) and at a large scale in the whole Mediterranean Sea. High levels of genetic diversity were found in Sardinian populations, being significantly different from other areas of the Eastern Mediterranean Sea due to the biotic and abiotic factors here discussed. Sardinian torpedoes can hence be indicated as priority populations/areas to be protected within the Mediterranean Sea. Moreover, sequence data confirmed that only the three species occur in the investigated area. The application of several ‘species-delimitation’ methods found evidence of cryptic species in the three species outside the Mediterranean Sea, as well as in other genera/families, suggesting the urgent need for future studies and a comprehensive revision of the order Torpediniformes for its effective conservation.