Phylogeny of Somniosus sleeper sharks: insights from newly sequenced mitochondrial genomes

Mitochondrial DNA (mtDNA) has been extensively used to explore phylogenetics since the its use became available. This science is considered useful in discerning relationships and evolutionary histories that are not possible with morphological studies alone. The sleeper sharks (genus: Somniosus) are a group of poorly understood, long-lived, iconic species whose taxonomic status within the genus have been argued about for many years. The aim of this study was to sequence and characterize mitogenomes of all Somniosus species to gain a better phylogenetic understanding of the genus and to discriminate the delimitations between species. Using next-generation sequencing, complete to nearly-complete mitogenomes were assembled of all species within Somniosus. Clear divergence was shown between the subgenera S. Somniosus and S. Rhinoscymnus, estimated at 7.8 million years ago, with no discernable differentiation between Somniosus pacificus and Somniosus antarcticus, nor between Somniosus rostratus and Somniosus longus. The results suggest a panmictic population of Somniosus pacificus and Somniosus antarcticus, as well as between Somniosus rostratus and Somniosus longus. Combined, the results of this study show that a thorough revision is needed of the Somniosus genus to improve taxonomic resolution and allow more informed conservation related decisions to be made.