Research Project
Full description The billfishes of the suborder Xiphioidei consist of 10 species of epi-pelagic fish separated between the families Xiphiidae and Istiophoridae. The broadbill swordfish (Xiphias gladius) is monotypic within the family Xiphiidae, with all other billfishes placed in Istiophoridae. The taxonomic classification for the billfishes was originally proposed by Nakamura (1985) based on morphological characters, however, recent advances in DNA sequencing technologies have made more molecular markers available for billfish phylogenetics. From the outcomes of phylogenetic investigations using partial nuclear and mitochondrial (mtDNA) sequences a restructuring of the Istiophoridae was suggested, which included the expansions of the three existing genera into five. Since this phylogenetic work it has been acknowledged that several aspects of the Istiophoridae phylogeny remain unresolved including; (1) the placement of the genus Istiompax in relation to other taxa (2); the lack of resolution among species in the genus Tetrupturus; and (3) the inability to differentiate species within Kajikia based on mtDNA sequence data. We sequenced the whole mitogenomes for all istiophorid billfish species to test whether the phylogenetic hypothesis of five genera proposed by previous phylogenetic analysis are supported using whole mitogenome data and whether this data could clarify unresolved taxonomic issues. Our analysis of whole mitogenome sequences supported the restructuring of Istiophoridae into five genera and confirms placement of Istiompax at the sister taxon to Kajikia + Tetrapturus. Genetic distances between K. audax and K. albida were found to be smaller than between Indo-Pacific and Atlantic clades of both M. nigricans and I. playpterus. Our results demonstrate the complex evolutionary history of the billfishes.