School of BioSciences - Theses
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ItemLack of transferability of experimentally enhanced thermal tolerance of photosymbionts between coral larvae and sea anemone hosts( 2021)Coral reefs support a wide range of marine species and are crucial for our economy. However, current climate change and associated summer heatwaves cause reduced coral health and high mortality rates. An important aspect of coral reefs is a mutualism between the cnidarian host and endosymbiotic algae in the family Symbiodiniaceae, which provide more than 90 % of the coral energy through photosynthesis under the healthy mutualistic relationship. However, stressful environmental conditions such as elevated ocean temperature cause coral bleaching, which is the loss of Symbiodiniaceae from coral tissues. To increase the thermal tolerance of the corals, heat-evolved strains of the Symbiodiniaceae species Cladocopium C1acro were previously obtained through experimental evolution in vitro. Of the ten heat-evolved Symbiodiniaceae strains, three strains confer enhanced bleaching tolerance to Acropora tenuis coral larvae. To test whether these strains improve the thermal tolerance of another host species, I exposed sea anemones, Exaiptasia diaphana, inoculated with each of eight strains of Symbiodiniaceae (the homologous symbiont, Breviolum minutum; the wild-type and six heat-evolved strains of Cladocopium C1acro) to elevated temperature. My findings showed that the thermal tolerance of E. diaphana varied depending on the inoculated Symbiodiniaceae strains, however, the thermal tolerance ranking differed from that observed in the previous coral larval experiment. Metabolomics analysis of the host fraction indicated that the translocation of sugar was significantly lower under the elevated temperature treatment for all host-symbiont pairs, which supports one of the bleaching hypotheses that coral bleaching is caused Symbiodiniaceae becoming parasitic under elevated temperature. This study revealed important insight into the cnidarian-Symbiodiniaceae interaction under elevated temperature and provided an insight into the coral bleaching hypothesis.
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ItemThe diversity and behaviour of Dermaptera (earwigs) in the southern Australian grain belt( 2018)Dermaptera (earwigs) are a cosmopolitan order of insects that have recently come to the attention of the Australian grain industry. Researchers have been sampling Dermapteran diversity and abundance across the southern Australian grain belt, but resolution of the sample is stifled by taxonomic impediment, particularly for specimens of the morphologically uniform Anisolabididae family. Molecular methods can provide much needed resolution to the study of Australian Dermaptera. I barcoded known Dermaptera species from across the southern Australian states to assess the utility of barcoding for Dermapteran biodiversity research. I also assessed the diversity of the Anisolabididae by combining morphological identification and DNA barcodes. I then estimated their phylogeny with a larger molecular dataset comprised of two mitochondrial and two nuclear gene fragments under a maximum-likelihood framework. Anisolabididae males were divided into seven morphospecies based on the shape of the forceps and parameres (a male genital structure), and these morphospecies were corroborated by barcodes (low within versus between-species genetic distance). Paramere shape distinguished two putative genera, Anisolabis Fieber and Gonolabis Burr. The molecular phylogeny did not support the monophyly of the genera, rather forming clades distinguished by the shape of the forceps. The evolutionary significance of paramere versus forceps morphology in Dermapteran taxonomy is discussed. Anisolabididae were only found in Western and South Australia and showed apparent endemism. Extending the study of Australian Anisolabididae beyond grains-producing regions may reveal a diverse endemic fauna, almost entirely unexplored heretofore.
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ItemDinoflagellate endosymbionts of corals (Symbiodiniaceae) closely associate with a diversity of bacteria( 2019)The ecological success of coral reef ecosystems is dependant on their obligate endosymbiosis with dinoflagellates in the family Symbiodiniaceae. This symbiosis does not occur in isolation; a diverse community of bacteria contribute to coral health and functioning. Though microbial-coral relationships are well studied, and dinoflagellate-bacterial associations are abundant in the marine environment, limited research focuses on Symbiodiniaceae-bacterial interactions. We combined autofluorescence quenching of Symbiodiniaceae with fluorescence in situ hybridisation to create three-dimensional reconstructions. These results present the first conclusive evidence that six species of Symbiodiniaceae harbour intracellular bacteria as well as cell surface associated extracellular bacteria. Hybridisation of class specific probes (Gammaproteobacteria, Alphaproteobacteria and Flavobacteriia) showed that taxonomic affiliation of intracellular bacteria differed between Symbiodiniaceae species. Furthermore, 147 members from the phyla Proteobacteria, Bacteroidetes and Firmicutes were isolated from ex hospite Symbiodiniaceae. Low diversity of cultured bacterial symbionts suggest that Symbiodiniaceae are selective in their association with bacteria. Based on the diversity and functional potential of Symbiodiniaceae-bacterial associations microbial interactions should no longer be ignored as potentially contributing to the coral holobiont health and functioning.