Use of rapidly evolving molecular markers to distinguish species and clarify range uncertainties in the spearfishes (Istiophoridae, Tetrapturus)

Despite broad spatial distributions in the Atlantic, Pacific, and Indian oceans, relatively little is known about spearfishes (family Istiophoridae, genus Tetrapturus) due to their pelagic nature and relative scarcity. The limited biological understanding of spearfishes includes uncertain taxonomic relationships complicated by conserved morphology, thus specific identification relies heavily on geographic location of capture. Previous phylogenetic studies incorporating a limited number of loci and few representatives of each species have been unable to consistently resolve the four currently recognized species comprising Tetrapturus. In the present study, we surveyed 14 nuclear microsatellite loci and the mitochondrial DNA control region across relatively large numbers of samples per species to genetically discriminate spearfish species. Molecular data resolved roundscale spearfish (n = 89) (Tetrapturus georgii Lowe, 1841) and Mediterranean spearfish (n = 12) (Tetrapturus belone Rafinesque, 1810) as genetically distinct groups. Longbill spearfish (n = 79) (Tetrapturus pfluegeri Robins and de Sylva, 1963) and shortbill spearfish (n = 29) (Tetrapturus angustirostris Tanaka, 1915) were not consistently resolved. A single individual collected in the western central Atlantic Ocean off Brazil assigned to shortbill spearfish and likely represents a vagrant. Additionally, a spearfish sampled from the Indian Ocean off eastern South Africa was morphologically identified as a longbill spearfish, and the molecular profile of this specimen was consistent with the morphological identification. Our study represents the most extensive molecular evaluation of the spearfishes to date. Results reported here underscore the substantial level of genetic similarity between longbill and shortbill spearfishes, and suggest high-resolution genomic methods may be required to unambiguously resolve these species.