Mitogenomics of electric rays: evolutionary considerations within Torpediniformes (Batoidea; Chondrichthyes)

Torpediniformes (electric rays) is a relatively diverse group of benthic coastal elasmobranchs found in all shallow tropical to temperate waters around the world. Despite its ecological and evolutionary importance, the inter-relationships within this lineage of cartilaginous fishes and its phylogenetic position within Batoidea remain controversial. In this study, we report the first complete sequences of two tropical electric rays, Narcine bancroftii and Narcine brasiliensis, using a combination of 454 and Sanger sequencing technologies. These species are a common bycatch of artisanal fishery communities on the north-east Caribbean coast of Colombia and are considered Critically Endangered according to the International Union for Conservation of Nature classification system. Overall, the two newly sequenced mitogenomes exhibit similarities in size, transcriptional orientation, gene order, and nucleotide composition in comparison to other batoids. Based on the concatenated alignment of protein-coding genes, our phylogenetic analyses support the hypothesis that electric rays are closely related to thornback rays (Platyrhinidae), forming a clade in a sister position to a group containing the remaining three batoid orders. Within Torpediniformes, our results reject the nonmonophyletic hypothesis of the genus Narcine reported in previous morphological and molecular studies.