Evaluating the importance of geothermal areas in providing refugia for Antarctic springtails through the Pleistocene glaciations
Date
2015
Authors
Smith, Laura
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Abstract
Environmental change can cause shifts in species’ distributions and affect the spatial structure of biodiversity. Pleistocene glacial cycles, for example, generally resulted in large changes to species’ ranges, reflected by lower contemporary diversity in newly-colonised areas versus long-term refugia. Antarctic glaciers would have been more extensive at the Last Glacial Maximum (LGM) than today, and despite a lack of evidence for ice-free refugia, terrestrial species appear to have survived on the continent for millions of years. Antarctica has multiple volcanoes that have been active since before the LGM, and geothermally warmed soils could have provided suitable ice-free environments for terrestrial species. Spatial patterns of species richness in plants and fungi have already revealed that geothermal areas are likely to have played an important role in species survival during glaciations. The influence of geothermal areas on the survival of fauna has yet to be robustly tested.
Under a hypothesis of geothermal refugia, higher diversity would be expected near geothermal areas compared to non-geothermal terrestrial ecosystems, and there should be a gradient of decreasing diversity with distance from these areas. This study explored whether geothermally heated areas could have provided refugia for Antarctic springtails (Collembola) during the LGM. Spatial patterns of genetic diversity in the Antarctic springtail Gomphiocephalus hodgsoni in southern Victoria Land were examined using novel mitochondrial DNA (mtDNA) data from markers COI and 16S. Meta-analyses were performed using published mtDNA data from five species of Antarctic springtails, including G. hodgsoni.
The results of this research, however, do not provide support for geothermal refugia. Generalised linear mixed models produced by the meta-analyses of COI and COII data for five springtail species did not show a relationship between genetic diversity and distance from nearest volcano. Populations of G. hodgsoni on Ross Island, close to volcanic Mt Erebus, were characterised by low genetic diversity, whereas populations in the McMurdo Dry Valleys had higher genetic diversity. Multiple population expansion events were inferred for G. hodgsoni, indicating that there may have been several glacial refugia in Victoria Land.
This study has highlighted some of the challenges in determining the locations of glacial microrefugia, such as the selection of appropriate spatial scales, the resolution of molecular markers, and the confounding influence of landscape complexity (e.g. the presence of multiple volcanoes in Victoria Land). Interdisciplinary collaboration between the fields of geomorphology and molecular ecology, as well as the use of genome-wide SNP data for improved resolution of fine-scale genetic patterns, may help resolve the locations of habitable ice-free areas during the LGM. The patterns of genetic diversity and population structure in G. hodgsoni that were demonstrated in this study improve our knowledge of evolutionary processes affecting Antarctic organisms, and may help to inform conservation management of terrestrial biodiversity in Victoria Land.
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Thesis (Honours)