School of BioSciences - Theses
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ItemSystematics and biogeography of Spyridium with a focus on Spyridium parvifolium and its hybrids( 2022)Spyridium is a genus of c. 45 species endemic to south-western and south-eastern Australia, with a disjunct distribution across the Nullarbor Plain and Bass Strait. The genus also includes several morphologically distinct phrase name taxa. Spyridium parvifolium is a widespread and morphologically variable shrub from south-eastern Australia. Several varieties and forms of this species have been recognised, but there is disagreement on the accepted taxonomy between Australian states. Spyridium parvifolium is known to hybridise with S. daltonii in the Grampians and is thought to hybridise with S. vexilliferum in locations where these taxa co-occur in western Victoria and south-eastern South Australia. The aim of this research project was to develop a comprehensive molecular systematic understanding of Spyridium, and S. parvifolium and its hybrids, to inform the treatment of Rhamnaceae in the Flora of Australia (Kellermann et al. 2022-). The objectives were to investigate: the species circumscription and biogeographic history of Spyridium, the infraspecific taxa and phylogeographic patterns of S. parvifolium and introgression associated with this species (i.e. S. xramosissimum and S. parvifolium x S. vexilliferum). Entire chloroplast genomes (c. 160k base pairs) and the nuclear ribosomal array (18S–5.8S–26S; c. 6k base pairs) were analysed using both Bayesian and Maximum Likelihood phylogenetic methods. In total sequences from 230 samples were analysed across these phylogenies, including representatives of all recognised species of Spyridium, six phrase name taxa, seventy-two accessions of S. parvifolium, eight putative hybrids and four outgroup taxa. This study provides the most comprehensive phylogenies of Spyridium and S. parvifolium to date. For Spyridium, several biogeographic patterns were identified, including deep diverging clades of taxa endemic to Western Australia, New South Wales and Tasmania. Several taxa were identified as polyphyletic (e.g. S. eriocephalum and S. phylicoides), warranting taxonomical review. For S. parvifolium, early divergence of individuals from west of the Murray Darling Depression, isolation on the inland side of the Great Dividing Range and recent seed-mediated gene-flow across Bass Strait were identified in the chloroplast genome phylogeny. The variants of S. parvifolium were not supported as genetically distinct suggesting the infraspecific recognition of var. parvifolium and var. molle in Tasmania is not warranted. Molecular evidence of introgression between S. parvifolium and both S. daltonii and S. vexilliferum was identified, providing molecular support for hybrids also inferred from intermediate morphology. Other findings include inferred parentage, unidirectional introgression and recombination of the nuclear ribosomal array for some hybrid accessions.
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ItemComparative phylogeography and diversity of Australian Monsoonal Tropics lizards( 2016)Tropical savannah biomes cover ~20% of the world’s landmass, however the biodiversity encompassed within these environments and the underlying processes that have shaped it remain poorly understood. Recent increased research to address this knowledge gap have begun to reveal surprisingly high amounts of deep, geographically-structured diversity, much of which is cryptic or hidden within morphologically similar species complexes. These patterns are especially emphasized in vertebrate taxa which are intrinsically linked to rock escarpments and ranges that dissect the savannah woodlands and grasslands of many of these biomes, hinting at a role of heterogeneous topography in structuring diversity. The remote Australian Monsoonal Tropics (AMT) spanning the north of the Australian continent is a particularly vast, and relatively undisturbed, tropical savannah region. Recent increased surveys are revealing numerous new species and endemism hotspots, indicating we are only just beginning to uncover the true biodiversity levels within this biome. Not only is there a relative paucity of knowledge regarding the present diversity within this region, but there is also limited understanding of how this diversity came to be. Phylogeographic studies can assist us in establishing current patterns of diversity and their evolutionary significance within regions and biomes. Furthermore, by comparing and contrasting the patterns and timing of diversification within and between biomes for multiple ecologically diverse taxa, we can begin to elucidate the history of these biomes and the environmental processes that have shaped the diversity we observe today. In this dissertation I aimed to better assess and establish true patterns of biodiversity and endemism within the Kimberley region of the AMT (Western Australia), and to place these patterns within a broader continental context using intra- and inter-biome comparisons in related taxa. Using geckos as a model system I took a comparative phylogeographic approach, integrating advanced next-generation genetics and morphology to establish patterns and timing of diversification across ecologically variable taxa. Within all Kimberley taxa I studied, I uncovered high levels of cryptic diversity. Much of this diversity involves especially short-range endemic lineages concentrated in key regions typically with one or more of the following factors: highly mesic conditions, island or insular environments, and unique or complex geological formations. In recognising these areas I have provided evidence of novel biodiversity hotspots and emphasised the significance of others as representing important “refugia” within the Kimberley that allow persistence and facilitate divergence of lineages through harsh periods of environmental change. These findings indicate diversification patterns are shaped by complex interactions of climatic variation, topography, and species’ ecology, allowing inference of biogeographic history and a greater ability to predict impacts of future environmental change.