DNA barcoding flags the existence of sympatric cryptic species in the slender codling Halargyreus johnsonii Günter, 1862 (Gadiformes, Moridae)

Abstract

According to current systematics, the genus Halargyreus Günther, 1862 is composed of a single valid, widely distributed species, called H. johnsonii Günther, 1862, although DNA barcoding has previously suggested that specimens from New Zealand and Tasmania may belong to a different species. This research doubles the number of DNA barcodes of this species available in public repositories and expands the locations of the catches thereby allowing a better estimation of its intraspecific variability. A cladistic analysis of haplotype associations shows two independent clusters that could represent different species. These groupings overlap geographically in the North Atlantic Ocean, discarding the possibility of allopatry as previously proposed for the sequences from New Zealand and Tasmania. Similarly, none of the clusters could be assigned to H. johnsonii taking into account that the holotype comes precisely from the North Atlantic Ocean. Sequences from New Zealand and Tasmania are hierarchically linked to sequences from the North Atlantic, whereas other sequences from the South Seas, together with sequences from the North Atlantic and Pacific, form an independent group with no hierarchical link to the former. These preliminary results indicate not only the need to delve deeper into the systematics of the genus Halargyreus, but also suggest the existence of a complex of cryptic species of which an attempt should be made to clarify using the combined traditional and molecular taxonomies.