Abstract
Advancements in taxonomic understanding of species are critical to addressing the global biodiversity crisis. The application of modern genetic approaches and the results of molecular research are fundamental for identifying, describing, managing and conserving threatened species. Over recent decades, the application of molecular techniques has revolutionised our understanding of the diversity of native fishes in New Zealand, facilitating the discovery of several previously cryptic species.
The evolution of taxonomic knowledge on the diversity of New Zealand’s freshwater fishes has focussed primarily on the Galaxias genus of the Galaxiidae family, which comprise many of the most threatened species of freshwater fishes in New Zealand. Scientific research across multiple fields focusing on the Galaxias vulgaris species complex, a group freshwater-resident species of galaxias fishes endemic to the South Island of New Zealand, has been fuelled by morphological similarity between the species complex and their diadromous relative, Galaxias brevipinnis, in addition to their intrinsic and interesting reflections of the geological and geographical evolution of the South Island of New Zealand. The species complex comprises six recognised species: G. vulgaris (sensu stricto), G. anomalus, G. depressiceps, G. pullus, G. eldoni, and G. gollumoides. Additional diversity within this complex is illustrated by several additional lineages awaiting formal description, including: G. “Teviot”, G. “southern”, G. “species D”, G. “northern”, G. “Nevis”. and G. “Pomahaka”, although the number of recognised lineages and criteria used to define them has varied for close to thirty years.
This thesis addresses the phylogenomic relationships of the species-rich Galaxias vulgaris species complex using data generated through genotyping-by-sequencing (52,352 filtered SNPs and 319 million bp of sequences). As well as addressing knowledge gaps through resolving relationships among currently recognised lineages and providing support for formal descriptions, my research provides strong genomic evidence for a new species located in the Clutha River and Tokomairaro river systems of Otago, which I here name Galaxias “species Z” to avoid taxonomic and geographic confusion with previously recognised Galaxias “species D” that also occurs in the Clutha.
The genomic results of this research support significant taxonomic advances to threatened fishes in the South Island of New Zealand, complementing recent conservation genomic studies of freshwater fishes in other regions of the globe. These studies should lead to enduring conservation outcomes, as they inform potential description of species and assign populations to these species. Such new knowledge is essential for addressing the global biodiversity crisis.