Population genetic structure of escolar (Lepidocybium Xavobrunneum)

Escolar (Lepidocybium Xavobrunneum) is a large, mesopelagic Wsh that inhabits tropical and temperate seas throughout the world, and is a common bycatch in pelagic longline Wsheries that target tuna and swordWsh. Few studies have explored the biology and natural history of escolar, and little is known regarding its population structure. To evaluate the genetic basis of population structure of escolar throughout their range, we surveyed genetic variation over an 806 base pair fragment of the mitochondrial control region. In total, 225 individuals from six geographically distant locations throughout the Atlantic (Gulf of Mexico, Brazil, South Africa) and PaciWc (Ecuador, Hawaii, Australia) were analyzed. A neighbor-joining tree of haplotypes based on maximum likelihood distances revealed two highly divergent clades ( = 4.85%) that were predominantly restricted to the Atlantic and Indo-PaciWc ocean basins. All Atlantic clade individuals occurred in the Atlantic Ocean and all but four PaciWc clade individuals were found in the PaciWc Ocean. The four Atlantic escolar with PaciWc clade haplotypes were found in the South Africa collection. The nuclear ITS-1 gene region of these four individuals was subsequently analyzed and compared to the ITS-1 gene region of four individuals from the South Africa collection with Atlantic clade haplotypes as well as four representative individuals each from the Atlantic and PaciWc collections. The four South Africa escolar with PaciWc mitochondrial control region haplotypes all had ITS-1 gene region sequences that clustered with the PaciWc escolar, suggesting that they were recent migrants from the Indo-PaciWc. Due to the high divergence and geographic separation of the Atlantic and PaciWc clades, as well as reported morphological diVerences between Atlantic and Indo-PaciWc specimens, consideration of the Atlantic and Indo-PaciWc populations as separate species or subspecies may be warranted, though further study is necessary.