Taxonomic re-appraisal for toothfish (Dissostichus: Notothenioidea) across the Antarctic Polar Front using genomic and morphological studies.

The Patagonian toothfish, Dissostichus eleginoides, is one of the largest predatory fishes inhabiting Southern Ocean waters spanning the Antarctic Polar Front (APF), a prominent biogeographic boundary restricting gene flow and driving species divergence between Antarctic and sub-Antarctic waters. In the light of emerging threats to toothfish conservation and sustainability, this study investigated genetic [mtDNA sequences and genome wide nuclear single nucleotide polymorphisms (SNPs)] and morphological data to critically evaluate the taxonomic status of toothfish north (Chile and Patagonian shelf) and south (South Georgia and South Sandwich Islands) of the APF. mtDNA revealed reciprocally monophyletic lineages on either side of the APF with coalescent analysis indicating these diverged during the Pleistocene. Integration with data from other sources suggests the Chilean/Patagonian lineage is endemic. SNP analysis confirmed restricted nuclear gene flow between both groups and revealed a consensus suite of positive outlier SNPs compatible with adaptive divergence between these groups. Finally, several morphological features permit unequivocal assignment of individuals to either of the clades. Based on the genetic, phenotypic and ecological divergence, the authors propose that toothfish on either side of the APF be recognised as distinct species, with the name D. eleginoides used for toothfish occurring in South American waters north of the APF and toothfish south of the APF being classified using the new name D. australis reflecting their southern distribution.