Comparative analysis of the mitochondrial genomes of Smoothhound sharks provide insight into the phylogenetic relationships within the family Triakidae

The genus Mustelus comprises demersal smoothhound sharks, including M. canis and M. norrisi. Despite their economic value and known conservation concerns, only a few genetic and no genomic resources exist for these two species. In this study, we assembled and described the complete mitochondrial genomes of Mustelus canis and M. norrisi. The mitochondrial genomes of M. canis and M. norrisi are 16,758 bp and 16,769 bp in length, respectively. Both mitogenomes are A + T rich and contain 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, 22 transfer RNA genes, and a control region (CR) 1122 bp and 1121 bp in length, respectively. Mitochondrial synteny observed in M. canis and M. norrisi is identical to that previously reported for congeneric species. In the studied mitochondrial genomes, all PCGs experienced purifying selection. In both species, 21 of the 22 tRNA genes exhibited a typical ‘cloverleaf’ secondary structure, except trnS1 that lacked a complete D-arm. The CR of the studied species lacked tandem repeats, but abundant A + T rich dinucleotide microsatellites were detected. Maximum likelihood and Bayesian inference phylogenetic analyses based on translated PCGs supported the monophyly of the family Triakidae. The same analyses indicated that the genus Mustelus was not monophyletic considering that all representatives of the genus Mustelus clustered together with Triakis megalopterus in a fully supported clade. The assembled mitochondrial genomes will aid with the accurate identification of specimens belonging to the genus Mustelus and support biomonitoring programs based on environmental DNA (eDNA).