The diversity and population genetic structure of Collembola (springtails) in Namib and Antarctic desert environments
Collins, G. E. (2019). The diversity and population genetic structure of Collembola (springtails) in Namib and Antarctic desert environments (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/13166
Permanent Research Commons link: https://hdl.handle.net/10289/13166
Desert soil invertebrates have limited dispersal opportunities, and isolated populations become increasingly divergent over generational time. There remains a paucity of genetic data available for invertebrates in desert environments, both hot and cold. This thesis is focussed on addressing this knowledge gap through phylogeographic studies of springtails (Collembola), primitive insect-like invertebrates and prominent soil inhabitants, in two contrasting geographic regions – the Namib Desert, Africa and ice-free areas in the Ross Sea region, Antarctica. Springtails were individually sequenced for variation in mitochondrial DNA (COI) and 865 sequences were obtained in total. Highly geographically structured and genetically-distinct populations were found within each study area, suggesting long-term vicariance. These findings are discussed relative to past geographical events and in the context of future warmer climate scenarios. This is of particular relevance, as future climate changes are predicted to exacerbate desertification in the Namib and promote deglaciation in the Antarctic. In the Namib Desert, only four springtail species have been documented, of which none had previously been sequenced, and detailed traditional taxonomic information (morphological) was lacking. This study generated 341 COI sequences for springtails that were extracted from soil samples collected across two Namib Desert transects (60 – 190 km), and 30 putative species were delineated based on analytical methods. Most diversity was found in the widespread genus Folsomides, where 26 genetically-distinct lineages were identified. As most of these putative species were restricted to individual sites across the desert, dispersal among locations is likely extremely limited under the present-day climate. Ten endemic springtail species are known from the Ross Sea region of Antarctica, each restricted to one of the region’s three Antarctic Conservation Biogeographic Regions: North Victoria Land (NVL), South Victoria Land (SVL) and the Transantarctic Mountains (TAM). The second part of this thesis synthesises all existing COI sequences (n = 937) from the literature for all springtails throughout these three bioregions, and contributes 524 new sequences representing nine of the ten species. Within each bioregion, differences in distributional range and population genetic structure were identified among species, suggesting differing evolutionary histories. Geographical features were identified as contemporary barriers to springtail dispersal. Furthermore, specific locations were found to harbour genetically distinct springtail populations and are highlighted as potential sites of conservation importance. In addition, COI sequences were assembled for springtails that had been collected over the past 20 years throughout SVL and TAM. Based on molecular clock analyses, genetically distinct lineages for the three widespread springtail species in this region have likely been isolated for between 5.54 and 3.52 million years, while the remaining species, which were more range-restricted, have diverged more recently (< 2 million years ago). These findings provide biological evidence to corroborate geological and statistical modelling of the past extents of ice sheets. The extent of glaciation throughout the last five million years has likely played a key role in the dispersal opportunities available to Antarctic Collembola and resulted in their present-day patterns of diversity.
The University of Waikato
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