Bio21 - Theses
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ItemClimate adaptation in Eucalyptus microcarpa (Grey Box) and implications for conservation( 2017)Restoration is an important component of conservation management, especially in highly modified landscapes. In the face of rapid environmental change, the mere presence of vegetation doesn’t necessarily equate to the long term sustainability of populations. Rather, there is a need to consider evolutionary potential in conservation planning, including restoration. This thesis investigates two key components of evolutionary potential pertinent to restoration – namely genetic diversity and climate adaptation – in an important restoration tree species in south-eastern Australia, Eucalyptus microcarpa. This thesis aims to understand how genetic diversity and local adaptation are distributed across the range of E. microcarpa and how this knowledge may help inform seed sourcing and enhance resilience of restoration plantings under climate change. To begin, I use a landscape genomic approach to explore genomic diversity in E. microcarpa and how diversity in small habitat remnants and revegetation (restored) sites compare to large remnants. This work found that small, habitat remnants and revegetation sites largely, but not completely captured patterns of genomic diversity across the landscape. Whilst overall genomic diversity was similar between site types, patterns of diversity across the genome varied between site types. These results suggest important genomic differences between site types that may influence future adaptive potential of revegetation sites and small habitat remnants. I then investigated adaptation to climate in E. microcarpa using multiple approaches. Firstly, using a landscape genomic approach, I found evidence of genomic climate adaptation in E. microcarpa. These results suggest climate adaptation to be a genome-wide phenomenon, involving many genes and genomic regions. Exploration of genomic changes that may be required to match projected climate change suggest adaptation to be via shifts in allele frequency from standing variation. In addition to suggesting a number of climate variables associated with adaptation in E. microcarpa, these results highlight the importance of genetic diversity and standing variation for maintaining adaptive potential. Utilising existing genetic resources for this species, I found evidence of heritable, genetic variation in growth and leaf traits of E. microcarpa growing in a provenance trial. Furthermore, significant trait variation between provenances and associations with climate variables suggest climate as a driver of adaptive differences. Finally, I combined the independent genomic and phenotypic analyses to provide stronger support for climate adaptation in E. microcarpa, including links between genomic variants and adaptive traits. Associations between traits and single nucleotide polymorphisms (SNPs) using putatively adaptive SNPs genotyped in provenance trial trees validated genomic results, suggesting some trait variation could be explained by these SNPs. Furthermore, links between all three sources of variation relevant to local adaptation – genotype, phenotype and climate – corroborated findings of the two independent analyses. This approach therefore provides greater support for adaptation to climate in E. microcarpa. Together these analyses address the current genetic state of restoration in E. microcarpa as well as the structure of genetic diversity and climate adaptation across its distribution. These results suggest adaptive differences within E. microcarpa that could be utilised to enhance evolutionary potential within restoration plantings.
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ItemParasitism by Trichogramma wasp: potential and reality under climate change scenario, with focus species attacking Asian corn borer( 2016)Climate change may directly influence the distribution of parasitoids, lead to phenological asynchrony with their hosts, and/or lead to other disruptions of multitrophic interactions. By determining the impacts of global warming effects which may influence Trichogramma populations, researchers and land users can be provided with ways to further enhance the efficiency of biocontrol. First, I identified common Trichogramma species emerging from Asian corn borer Ostrinia furnacalis egg masses (based on morphology and internal transcribed spacer 2- ITS-2) throughout southwestern Taiwan. I then compared their life history characteristics and thermal limits and determined the Wolbachia infection status of field-collected parasitoids. Although T. ostriniae and T. sp. y appear to be morphologically similar, the ITS-2 identity between these two taxa is only 89%. A commercially released Trichogramma colony thought to be T. chilonis possessed 99% identity with the field T. sp. y individuals. The current study provides a baseline for future work, and also highlights the importance of accurately identifying species when establishing colonies of natural enemies for biocontrol. Next, I evaluated the distributions of Trichogramma ostriniae and its native host, Ostrinia furnacalis (in southeastern Asia), and target host, Ostrinia nubilalis (in North America), using a combination of MAXENT and CLIMEX modelling approaches. Trichogramma ostriniae was predicted to occur in the summer corn region of China, with distribution limits linked to its sensitivity to cold, and the seasonality of radiation and precipitation. The stepwise modelling approach used here proved useful for assessing environmental factors linked to an egg parasitoid and its lepidopteran host and for identifying areas potentially suitable for inundative releases. Finally, integrating meta-analysis results and reviewing related literature, indicated that both top-down and bottom-up factors could moderate the effect size of egg parasitoids over a range of Extreme High Temperature (EHT) values. These patterns suggest a complex response to climate change, mediated by temperature factors, precipitation seasonality, crop type and perhaps other factors related to latitude. Trichogramma biocontrol efficiency is hampered by extreme climate change as they are more senstive to environmental factors than their hosts. The work presented here highlights effects of precipitation and radiation seasonality on parasitism, life history traits, and distributions of Trichogramma species, which could act to either improve or optimise the execution of lepidopteran biocontrol projects. Results of this study will be useful to managers for successful use of Trichogramma in biocontrol under a climate change future.
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ItemGeographic range and the mountain niche: ecology, adaptation and environmental change( 2015)The geographic range is one of the most fundamental traits of a species. For this reason, understanding the ecological and evolutionary drivers of the size, position, and structure of the range is a key research challenge. The geographic range also has an overriding influence on the environments to which a species is exposed and their spatial and temporal variation. This study addresses four questions relevant to understanding interactions between the environment and individuals, populations, species and communities, with a focus on mountain regions where environmental variation is particularly pronounced. First, using meta-analysis and a single-genus case study, I explore the relationship between geographic range size and characteristics of the ecological niche. Range size can vary by several orders of magnitude among closely related species, but is strongly and consistently associated with both niche breadth and niche position: the most widespread species tend to be those with a broader niche and/or those that utilise resources that are common across the landscape. Second, I investigate the relationship between niche and range limits by testing variation in physiological tolerance across environmental gradients in two mountain systems: beetles (Carabidae: Nebria Latreille) from the North American Cascade Range and grasshoppers (Acrididae: Kosciuscola Sjösted) from the Australian Alps. Whereas the Nebria, distributed across a 2000 m elevational gradient, showed almost no variation in thermal tolerance, the Kosciuscola showed significant interspecific variation in cold tolerance, consistent with the decrease in average temperature with elevation. I suggest that cold tolerance limits might constrain the upper range edge of at least one species. Third, I explore how past climate cycles and Australia’s dissected mountain landscape have influenced the population structure of an alpine-endemic grasshopper (Kosciuscola tristis) using a combination of genetic methods. Despite continuity of alpine habitat during Pleistocene glacial cycles and, by global standards, small-scale disjunctions in the present distribution of these environments, K. tristis showed deep lineage divergence associated with geographic breaks in alpine conditions. Fine-scale structure in the absence of clear geographic barriers suggests that habitat heterogeneity might structure populations at a regional scale. The last component of this work tests the response of alpine invertebrate species and communities to reduced winter snow cover. This is a likely future scenario in the Australian high country, where the winter snowpack is already marginal. I show that Australia has a diverse subnivean arthropod fauna, characterised by the high relative abundance of springtails (Collembola), mites (Acari), spiders (Araneae) and beetles (Coleoptera). Experimental reduction of the winter snowpack caused shifts in community composition, driven by a small number of abundant arthropod taxa. These effects were apparent at a small spatial and temporal scale, with rapid recovery from experimental perturbation in spring. Mountain ecosystems are threatened by climate change as they are already rare at a landscape scale, are typically fragmented and have limited scope for climate tracking. The work presented here highlights effects of small-scale environmental variation on species traits, genetic structure and communities, which could act to either buffer or exacerbate landscape-scale climatic changes.