Population genetic structure of Antarctic springtails (Collembola) and New Zealand damselflies (Odonata)
Since Darwin (Darwin, 1859), the process of speciation and maintenance of biological diversity has caused intensive debate in the scientific and non-scientific communities alike. The ability to analyze differences in the molecular structure of enzymes and DNA sequences has provided an extremely sensitive tool for investigating gene flow within and among populations, a key facet of the genetic divergence required for speciation to occur. Using such techniques, we are now able to gain a snapshot of the genetic structure of a population and its geographical distribution (Hewitt, 2001) In this way, the phylogeography of species from many environments around the globe have now been studied in fine detail. It has also been possible to generate hypotheses proposing restricted distribution in 'refugia' and subsequent recolonisation after climatic events such as glaciation have occurred. Refugia appear to be particularly important in shaping high latitude biodiversity (Willis & Whittaker, 2000). On such occasions the distribution of different populations may ultimately overlap again at a contact zone, and the species geographical subdivision may provide enough evidence to suggest speciation or the creation of a hybrid zone (Hewitt, 2001 ). In addition, the DNA sequences may yield important information on the evolutionary history, dispersal and taxonomy of various species. Morphologically indistinguishable organisms may be discovered as 'cryptic species', and vice versa, taxa considered to be very different based on observable characteristics can be found to be genetically similar and not reproductively isolated (e.g. Trewick, 2000; Witt & Hebert, 2000). In this way, the genetic diversity within and among closely related species may be determined to a high degree of resolution. In today's climate of human interference and relatively rapid environmental change, it is vital that we appreciate and make full use of the detailed population information available to us. In this way, we may be able to predict and potentially mitigate the consequences of environmental change for organisms by analyzing their evolutionary past. This thesis contains an analysis of molecular data (mtDNA and allozymes) on two arthropod taxa. The thesis consists of two chapters. Chapter I describes the distribution of mitochondrial (mt) DNA haplotypes for the Antarctic springtail Gomphiocephalus hodgsoni (Collembola) in Taylor Valley, southern Victoria Land. The observed distribution was congruent with a hypothesis of multiple refugia during the Pleistocene glaciations and a barrier to gene flow by a glacial lake. Chapter II assesses the genetic variability of the New Zealand damselfly genera (Odonata) from sites throughout the North, South and Chatham islands using both allozyme and mtDNA analyses. All morphologically recognized species were clearly discernible on the basis of both mtDNA and allozymes. However, variability within and among sites was limited for all species, and may have implications from a conservation perspective. The thesis ends with a brief summary section highlighting the main findings contained in the thesis and outlining potential future research directions.
Antarctic, Antarctic springtails, New Zealand
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