Abstract:
The complex climatic and geological history of New Zealand has hindered our understanding of the processes driving the evolution of New Zealand's biota. In this thesis, I investigated the relative roles of different climatic and geological processes in the recent evolutionary history of New Zealand using phylogeographic methods and the New Zealand common skink (Oligosoma nigriplantare) as a model taxon. Oligosoma nigriplantare consists of two subspecies; O. n. nigriplantare found in the Chatham Islands, and O. n. polychroma that is distributed throughout the southern North Island, much of the South Island and Stewart Island. Both subspecies are highly variable in morphology, behaviour and ecology which has led to a number of further distinct groups being proposed. Using phylogenetic and molecular analyses of mitochondrial DNA (ND2 and ND4) I found a high level of divergence (~9%) between O. n. nigriplantare and O. n. polychroma. These data suggest that O. n. nigriplantare and O. n. polychroma should be recognised as separate species. I found no support for any other previously proposed distinct groups within the species complex. Divergence time estimates indicated O. nigriplantare colonised the Chatham Islands within the last ~6.4 million years via transoceanic dispersal. I revealed patterns of both isolation by distance and restricted gene flow using analysis of molecular variance and nested clade analysis across the Chatham Islands, consistent with the history of sea level changes in the archipelago. Across the range of O. n. polychroma, five geographically distinct clades were revealed. The phylogeographic pattern and inferred age of these clades suggests mountain building during the Pliocene along active fault lines promoted their divergence 3.98-5.45 million years ago. A short interspersed nuclear clement polymorphism in the myosin gene intron (MYH-2) confirmed a pattern of restricted gene flow between lineages on either side of the Southern Alps. The straits between the main islands of New Zealand accounted for much less of the variation found within O. n. polychroma, most likely due to the repeated emergence of inter-island landbridges during the Pleistocene that facilitated gene flow. Overall, my research has found evolutionary independence of groups within the common skink species complex, providing valuable insight for the conservation management of this species. In the future, investigating the phylogeography of co-occurring species will reveal further details on the nature of these phylogeographic patterns and the processes driving evolution in New Zealand.
