Genetic diversity and phylogeography of New Zealand and Antarctic arthropods

Historical climatic and geological changes and ecological factors ( e.g. population size, dispersal abilities) are conducive to shaping genetic differentiation among natural populations. This thesis examines these issues in a phylogeographic context by looking at patterns of genetic diversity and dispersal of arthropods in two geographic regions. In southern New Zealand and its outlying islands, regional genetic divergence was revealed using mtDNA (COi) analysis for populations of idoteid isopods. Divergence within Austridotea benhami was < 2.0%. However, divergence within A. lacustris reached up to 10% with four main groupings: 1) Chatham Islands; 2) Campbell Island; 3) Fiordland; and 4) east coast South Island and Stewart Island. Similarly, A. annectens showed two main groups (4.4% diverg~nt): 1) Chatham Islands; and 2) east coast South Island and Stewart Island. These patterns are likely to be the result of geographical isolation, with some populations showing divergence corresponding to the availability of habitat (e.g. the divergence of A. lacustris and A. annectens on Chatham Islands may relate to the availability of this habitat - 4 Mya). Additionally, divergence of A. lacustris on Campbell Island and Fiordland may indicate a rare founder event or environmental change that resulted in population isolation. Overall, genetic data and geological history indicated that rare dispersal / events (or range expansion and population extinction), particularly during the Pliocene, may have played an important role in shaping the present-day distribution and genetic structure of freshwater idoteid isopods throughout New Zealand and its outlying islands. In Antarctica, analysis of patterns of mtDNA (COI) diversity and the geographic distribution of haplotypes among populations of the springtail Gomphiocephalus hodgsoni and the mite Stereotydeus mollis also revealed (congruent) patterns of genetic sub-structuring. Furthermore, genetic discontinuities suggested limited dispersal opportunities and isolation-by-distance for these taxa. Haplotype diversity within Wright and Victoria Valleys (St. John's, Olympus and Asgard ranges) was found to be higher here than in other areas and the distribution of haplotypes across sites was very heterogeneous. G. hodgsoni and S. mollis populations harboured eight and 23 new mtDNA haplotypes, respectively and showed links to previously sampled populations across southern Victoria Land. Accordingly, it is possible that this region may represent a primary location of a refugial source population from which many extant populations in southern Victoria Land have expanded since the Pleistocene and Holocene. Collectively, these studies revealed limited current dispersal and high levels of regional genetic differentiation for three arthropod taxa from fragmented habitats in both New Zealand and Antarctica. It provided insight into the biogeographic processes underlying modem distribution patterns of these taxa and highlighted the utility of the phylogeographic approach in reconstructing biotic history to further / knowledge of the relationships that exist between population processes and patterns of species diversity. Additionally, genetic analyses such as those performed here provided a basis to re-evaluate populations from a biodiversity perspective. Specifically, the New Zealand study clarified specific and generic relationships for potential reassessment of conservation status, while the Antarctic study identified biodiversity hotspots and priorities for conservation strategies (e.g. specially protected areas)