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    Molecular phylogenetic structure between geographically distant marine fish Macrourus holotrachys and M. berglax.
    (2021) Zuma, Nkululeko.; Miya, Tshoanelo Portia.
    The taxonomic status of Macrourus species has been in disarray due to their morphological similarities and overlapping distribution. Given the number of research that have been conducted in an attempt to resolve the taxonomic confusion in this group, there are still some species with unconfirmed taxonomy. Macrourus holotrachys found in the Southern Ocean and M. berglax from the North Atlantic Ocean, are among the species that need taxonomic review. These species differ morphologically, and the minor differences have been used as a basis to separate them into different species. DNA molecular studies that have reviewed the taxonomy of these species using the cytochrome c oxidase subunit I (COI) gene found low sequence divergence between M. holotrachys and M. berglax. The findings of these studies provide motivation for population genetic studies to compare genetic structure between these distantly distributed species. The present study aimed to close this gap by assessing the genetic structure between M. holotrachys and M. berglax using the COI and displacement loop (D-loop) gene regions. Aligned sequences of these genes were 532 base pairs (bp) and 703 bp long, respectively. The COI gene revealed seven haplotypes from 26 sequences, while D-loop region had eight haplotypes from 55 sequences. The mismatch distribution curves were unimodal and the haplotype network trees had a star shape pattern for both datasets, which is consistent with populations undergoing demographic expansion. Although neutrality test values were not significant, negative values were observed for Tajima’s D, supporting the populations undergoing demographic expansion. The FST pairwise distance method revealed no substantial differentiation between the populations of M. holotrachys and M. berglax. These results suggest that a recent dispersal of populations may have occurred such that there was not enough time for the separated populations to develop different genetic traits. In conclusion, this study demonstrated no significant genetic differentiation between M. holotrachys and M. berglax and confirms that they are one species consisting of North and South Pole populations, respectively. Additionally, this study has added more literature on the population genetic structure of these species.