| Popis: |
Antarctic marine biodiversity is largely contained in the continental shelf zone and is characterized by high levels of endemism and a high proportion of invertebrate species with brooding life histories. Benthic marine species in Antarctica are considered highly vulnerable to the predicted warming environment, and therefore there is an urgent need for research to aid their effective management and preserve biodiversity. Our knowledge of the processes affecting population genetic diversity and structure in the Antarctic benthos remains very limited, particularly in East Antarctica. The irregular heart urchins (genus: Abatus, Spatangoidea: Schizasteridae) are endemic to the sub-Antarctic and Antarctic regions, and their brooding life history is expected to restrict their dispersal capabilities, leading to isolated and potentially inbred populations that may be susceptible to the effects of environmental change. The broad aim of this thesis is to characterize the genetic diversity and structure of heart urchin populations at different spatial scales (hundreds of meters to thousands of kilometers) in order to elucidate past and contemporary processes affecting heart urchin populations in East Antarctica. Two mitochondrial markers (16S and COI) were used to examine large-scale phylogeographic relationships in Abatus ingens and Abatus nimrodi. Samples were collected near three Antarctic stations separated by over 1000 km: Davis, Casey, and Dumont D‚ÄövÑvºUrville. In addition, three other Abatus species: A. shackletoni, A. philippii, and A. cavernosus, and the closely related Amphipneustes lorioli, were included in the analysis in order to clarify taxonomic relationships within the genus. Large-scale genetic patterns were indicative of populations that survived in shelf refugia and experienced pronounced bottlenecks during Quaternary glaciations. Genetic diversity was higher at Davis than in Casey and Dumont D‚ÄövÑvºUrville for A. ingens and A. nimrodi. Populations of A. ingens from the three study areas were genetically distinct, while populations of A. nimrodi from Casey, and Dumont D‚ÄövÑvºUrville shared a single haplotype and were differentiated from Davis individuals. Phylogenetic inferences suggest that the species classified as A. nimrodi is more closely related to Amphipneustes lorioli than other Abatus spp. and requires taxonomic revision. Microsatellite DNA markers were developed from A. ingens to study the fine-scale (ca. 5km) patterns of population genetic diversity and structuring in the area surrounding Davis Station. The markers successfully cross-amplified in A. shackletoni and A. philippii allowing for a multispecies comparison. In order to test for potential impacts by anthropogenic pollutants, samples were taken at five sites at varying distances from the outfall of wastewater discharge from the station. There was no evidence of an effect of pollution from Davis Station on genetic variation, and patterns of population genetic differentiation varied among the species. Gene flow occurs across distances of at least 5km, which is not consistent with the hypothesis of limited dispersal associated with the brooding life history, and suggests life history is not a good predictor of fine-scale population structure in these species. There was genetic evidence of a long-term population decline in all three species, but the estimated timing at the decline precedes any likely impact due to anthropogenic activities. Furthermore, two genetic clusters inferred in A. ingens and A. shackletoni suggest secondary contact after population differentiation in glacial refugia. The declining effective population size inferred for these three benthic species highlights their fragility and the need for conservation concern. Taken together, the results from this study provide a significant insight into the processes that have shaped patterns of genetic diversity and structure of Antarctic heart urchin populations in East Antarctica. This research has implications for the management and preservation of Antarctic marine biodiversity. A clear influence from the cyclic glaciations of the Pleistocene on the present day population genetic differentiation patterns of the Antarctic heart urchin species studied is evidenced at both large and fine spatial-scales. The brooding development of these species does not appear to restrict their dispersal capabilities at fine spatial-scales, and population connectivity may be promoted by physical factors such as rafting on floating sea ice. The vulnerability of Abatus populations in East Antarctica was suggested by their reduced effective population sizes and population isolation at a large scale, which can contribute to a higher risk of local extinction. |
