Low levels of global genetic differentiation and population expansion in the deep-sea teleost Hoplostethus atlanticus revealed by mitochondrial DNA sequences

The orange roughy Hoplostethus atlanticus is a well-known commercial species with a global distribution. There is no consensus about levels of connectivity among populations despite a range of techniques having been applied. We used cytochrome c oxidase subunit I (COI) and cytochrome b sequences to study genetic connectivity at a global scale. Pairwise I broken vertical bar(ST) analyses revealed a lack of significant differentiation among samples from New Zealand, Australia, Namibia, and Chile. However, low but significant differentiation (I broken vertical bar(ST) = 0.02-0.13, P < 0.05) was found between two Northeast Atlantic sites and all the other sites with COI. AMOVA and the haplotype genealogy confirmed these results. The prevalent lack of genetic differentiation is probably due to active adult dispersal under the stepping-stone model. Demographic analyses suggested the occurrence of two expansion events during the Pleistocene period.