Molecular diversity and distribution of eastern Atlantic and Mediterranean dogfishes Squalus highlight taxonomic issues in the genus

Abstract

The alpha taxonomy of the globally distributed shark genus Squalus has been under intense investigation recently, and many new species have been described over the last decade. However, taxonomic uncertainty remains about several taxa. Without consistent nomenclature and the ability to reliably distinguish between the different Squalus species, basic data collection, downstream conservation and management efforts are seriously compromised. To aid in clarifying the taxonomic status of Squalus species in the eastern Atlantic and Mediterranean, we assessed species diversity at the molecular level and evaluated the consistency in species identification in the region. Samples from all nominal Squalus species recognized in the above regions were collected in an international effort and sequenced for regions of the mitochondrial COI and ND2 genes. These data were further analysed alongside publicly available sequences, including 19 of the 26 Squalus species globally recognized, to compare the regional genus‐level diversity with that found elsewhere. Our results confirm inconsistent species identification in the eastern Atlantic and Mediterranean Squalus, particularly concerning S. blainville and S. megalops, and reinforce the need to revise the status of S. megalops and S. mitsukurii as they may include several distinct species distributed around the world. The status of S. blainville is also discussed in the light of the current findings and its problematic taxonomic history.

Investigation on the genus Squalus in the Sardinian waters (Central-Western Mediterranean) with implications on its management

“…Both present and previous genetic data confirm that this taxon is widely distributed in the Mediterranean (Serena, 2005;Bat et al, 2005;Serena et al, 2009;Landi et al, 2014;Bonello et al, 2016;Kousteni et al, 2016;Cariani et al, 2017;Veríssimo et al, 2017).…”

“…Clade c6 comprised a single divergent sequence of a specimen from Libya, originally identified as S. blainville (Kousteni et al, 2016). Besides, sequences from Sardinia were strongly divergent from sequences in clades c1 (S. acanthias and S. suckleyi), and c8-c10 (individuals originally identified as S. megalops or S. blainville but belonging to distinct species still waiting formal description; Veríssimo et al, 2017). (Table S1).…”

“…Sequences were retrieved from GenBank (https://www.ncbi.nlm.nih.gov/ genbank). Cirrhigaleus australis was used as outgroup (Veríssimo et al, 2017). The list and details of the sequences used in the analyses are provided as supplementary table (Table S1).…”

“…Moreover, the analyses also included sequences of the species included in Group I (S. suckleyi) and Group II (S. cubensis, S. raoulensis, S. brevirostris) in the Squalus phylogeny by Veríssimo et al (2017). Sequences were retrieved from GenBank (https://www.ncbi.nlm.nih.gov/ genbank).…”

“…skull and teeth morphology) are used (Bonello et al, 2016). Moreover, Veríssimo et al (2017) reported that S. blainville and S. megalops are two names used almost interchangeably along the Eastern Atlantic and the Mediterranean Sea to identify the same species with the former mostly employed in the Mediterranean area while the latter in the Eastern Atlantic. Nevertheless, the results provided by those authors suggest that the 'true' S. megalops from Australia is not present in the eastern Atlantic and Mediterranean waters, but a different species that remains unidentified can occur (Veríssimo et al, 2017).…”