Assessing the effectiveness of DNA barcoding for exploring hidden genetic diversity in deep-sea fishes

Abstract

The numbers of deep-sea fish species and their genetic diversities are poorly understood because of taxonomic confusion and the lack of robust diagnostic features. However, DNA barcoding using mitochondrial DNA sequences may offer an effective approach to identifying cryptic species and characterizing their genetic diversities. To validate the genetic differentiation identified by DNA mitochondrial barcoding, it is necessary to show that these reflect variations present in nuclear genomic markers. Here, we performed DNA barcoding using cytochrome c oxidase subunit I (COI) sequences and also carried out multiplexed intersimple sequence repeat genotyping by sequencing (MIG-seq) for mesopelagic and demersal fish species from the continental shelf and upper slope of the northwestern Pacific Ocean. We obtained the COI sequences of 115 species from 48 families; the species were identified using the Barcode of Life Data System. Phylogenetic analyses using COI sequences showed high levels of intraspecific genetic differentiation (Kimura 2-parameter distances >2%) in 20 of 115 species, suggesting many cryptic species or intraspecific genetic differentiation previously unknown in these species. We performed phylogenetic and population genetic analyses using multiple single-nucleotide polymorphism loci obtained by MIG-seq of 3 species that showed high levels of intraspecific genetic differentiation in COI sequences. The nuclear markers confirmed the genetic differentiation in all 3 species identified by the COI sequences. The high concordance between these different genetic markers indicates the effectiveness of DNA barcoding for identifying cryptic deep-sea species and characterizing genetic differentiation in these species.