Graduate Theses & Dissertations

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Cytokinin biosynthesis, signaling and translocation during the formation of tumors in the Ustilago maydis-Zea mays pathosystem
Cytokinins (CKs) are hormones that promote cell division. During the formation of tumors in the Ustilago maydis-Zea mays pathosystem, the levels of CKs are elevated. Although CK levels are increased, the origins of these CKs have not been determined and it is unclear as to whether they promote the formation of tumors. To determine this, we measured the CK levels, identified CK biosynthetic genes as well as CK signaling genes and measured the transcript levels during pathogenesis. By correlating the transcript levels to the CK levels, our results suggest that increased biosynthesis and signaling of CKs occur in both organisms. The increase in CK biosynthesis by the pathosystem could lead to an increase in CK signaling via CK translocation and promote tumor formation. Taken together, these suggest that CK biosynthesis, signaling and translocation play a significant role during the formation of tumors in the Ustilago maydis-Zea mays pathosystem. Author Keywords: Biosynthesis, Cytokinins, Signaling, Translocation, Ustilago maydis, Zea mays
De novo transcriptome assembly, functional annotation, and SNP discovery in North American flying squirrels (genus Glaucomys)
Introgressive hybridization between northern (Glaucomys sabrinus) and southern flying squirrels (G. volans) has been observed in some areas of Canada and the USA. However, existing molecular markers lack the resolution to discriminate late-generation introgressants and describe the extent to which hybridization influences the Glaucomys gene pool. I report the first North American flying squirrel (genus Glaucomys) functionally annotated de novo transcriptome assembly with a set of 146,621 high-quality, annotated putative species-diagnostic SNP markers. RNA-sequences were obtained from two northern flying squirrels and two southern flying squirrels sampled from Ontario, Canada. I reconstructed 702,228 Glaucomys transcripts using 193,323,120 sequence read-pairs, and captured sequence homologies, protein domains, and gene function classifications. These genomic resources can be used to increase the resolution of molecular techniques used to examine the dynamics of the Glaucomys hybrid zone. Author Keywords: annotation, de novo transcriptome, flying squirrels, high-throughput sequencing, hybridization, single nucleotide polymorphisms
Comparative phylogeography in conservation biology
Phylogeographic histories of taxa around the Great Lakes region in North America are relevant to a range of ongoing issues including conservation management and biological invasions. In this thesis I investigated the comparative phylogeographic histories of plant species with disjunct distributions and plant species with continuous distributions around the Great Lakes region; this is a very dynamic geographic area with relatively recent colonisation histories that have been influenced by a range of factors including postglacial landscape modifications, and more recently, human-mediated dispersion. I first characterized four species that have disjunct populations in the Great Lakes region: (Bartonia paniculata subsp. paniculata, Empetrum nigrum, Sporobolus heterolepis, and Carex richardsonii). Through comparisons of core and disjunct populations, I found that a range of historical processes have resulted in two broad scenarios: in the first scenario, genetically distinct disjunct and core populations diverged prior to the last glacial cycle, and in the second scenario more recent vicariant events have resulted in genetically similar core and disjunct populations. The former scenario has important implications for conservation management. I then characterized the Typha species complex (T. latifolia, T. angustifolia, T. x glauca), which collectively represent species with continuous distributions. Recent microevolutionary processes, including hybridization, introgression, and intercontinental dispersal, obscure the phylogeographic patterns and complicate the evolutionary history of Typha spp. around the Great Lakes region, and have resulted in the growing dominance of non-native lineages. A broader geographical comparison of Typha spp. lineages from around the world identified repeated cryptic dispersal and long-distant movement as important phylogeographic influences. This research has demonstrated that comparisons of regional and global evolutionary histories can provide insight into historical and contemporary processes useful for management decisions in conservation biology and invasive species. Author Keywords: chloroplast DNA, conservation genetics, disjunct populations, invasive species, phylogeography, postglacial recolonisation
Using environmental DNA (eDNA) metabarcoding to assess aquatic plant communities
Environmental DNA (eDNA) metabarcoding targets sequences with interspecific variation that can be amplified using universal primers allowing simultaneous detection of multiple species from environmental samples. I developed novel primers for three barcodes commonly used to identify plant species, and compared amplification success for aquatic plant DNA against pre-existing primers. Control eDNA samples of 45 plant species showed that species-level identification was highest for novel matK and preexisting ITS2 primers (42% each); remaining primers each identified between 24% and 33% of species. Novel matK, rbcL, and pre-existing ITS2 primers combined identified 88% of aquatic species. The novel matK primers identified the largest number of species from eDNA collected from the Black River, Ontario; 21 aquatic plant species were identified using all primers. This study showed that eDNA metabarcoding allows for simultaneous detection of aquatic plants including invasive species and species-at-risk, thereby providing a biodiversity assessment tool with a variety of applications. Author Keywords: aquatic plants, biodiversity, bioinformatics, environmental DNA (eDNA), high-throughput sequencing, metabarcoding
Demographic history and conservation genomics of caribou (Rangifer tarandus) in Québec
Genetic variation is the raw material and basis for evolutionary changes in nature. The loss of genetic diversity is a challenge many species are facing, with genomics being a potential tool to inform and prioritize decision making. Whole genome analysis can be an asset to conservation biology and the management of species through the generation of more precise and novel metrics. This thesis uses whole genome re-sequencing to characterize the demographic history and quantify genomic metrics relevant to conservation of caribou (Rangifer tarandus) in Québec, Canada. We calculated the ancestral and contemporary patterns of genomic diversity of five representative caribou populations and applied a comparative population genomics framework to assess the interplay between demographic events and genomic diversity. When compared to the census size, NC, the endangered Gaspésie Mountain caribou population had the highest ancestral Ne:NC ratio which is consistent with recent work suggesting high ancestral Ne:NC is of conservation concern. These ratios were highly correlated with genomic signatures (i.e. Tajima’s D) of recent population declines and explicit demographic model parameters. Values of contemporary Ne, estimated from linkage-disequilibrium showed Gaspêsie having among the highest contemporary Ne:NC ratio. Importantly, classic conservation genetics theory would predict this population to be of less concern based off this metric alone. Inbreeding measures suggested nuanced patterns of inbreeding and correlated to the demographic models. This study suggests that while the Québec populations are all under decline, they harbour enough ancestral genetic variation to replenish any lost diversity, if conservation decisions are made in favour of these populations, specifically supporting NC. Author Keywords:
Reproductive Fitness of Smallmouth Bass (Micropterus dolomieu) Under Heterogeneous Environmental Conditions
Identifying the biotic and abiotic factors that influence individual reproductive fitness under natural conditions is essential for understanding important aspects of a species’ evolutionary biology and ecology, population dynamics, and life-history evolution. Using next generation sequencing technology, I developed five microsatellite multiplex reactions suitable for conducting large scale parentage analysis of smallmouth bass, Micropterus dolomieu, and used molecular pedigree reconstruction techniques to characterize the genetic mating system and mate selection in adult smallmouth bass nesting in Lake Opeongo, Ontario, Canada. I used multivariate spatial autocorrelation analysis to indirectly infer the occurrence and extent of natal philopatry among spawning adults, to assess the strength and direction of sex-bias in natal dispersal patterns, and to evaluate the degree of nest site fidelity and breeding dispersal of spawning adults. I also evaluated how differences in littoral zone water temperature caused by wind-induced seiche events influence the relative reproductive success of spawning adults. Lastly, I provide a synopsis of potential future research aimed at further exploring factors that influence the reproductive fitness of smallmouth bass in Lake Opeongo. This information will contribute to our understanding of the factors regulating smallmouth bass populations, and provide insight into the factors controlling the variance in individual reproductive success and thus recruitment dynamics in this species. Author Keywords: Dispersal, Fitness, Mate selection, Mating systems, Philopatry
Functional Investigation of A Ustilago maydis Xylose Metabolism Gene and its Antisense Transcripts
Ustilago maydis is a biotrophic fungal plant pathogen that causes ‘common smut of corn’ disease. During infection, U. maydis develops a metabolic dependency on its host, relying on uptake of the carbon molecules provided within Zea mays tissues. The research presented indicated a requirement for metabolism of the pentose sugar D-xylose through functional investigation of a U. maydis xylitol dehydrogenase (uxm1), an enzyme involved in the bioconversion of D-xylose. This work is the first to outline the importance of pentose metabolism during biotrophic plant pathogenesis, as U. maydis haploid cells lacking this gene were impaired in their ability to cause disease and grow on medium containing only D-xylose. This thesis also explored the possibility that expression of this carbon-related gene is controlled by antisense RNAs (asRNAs), endogenous molecules with complementarity to mRNAs. Previous investigation of U. maydis asRNAs identified some that are exclusively expressed in the dormant teliospore, suggesting they have a functional role within this cell-type. A subset of these asRNAs at the uxm1 locus were investigated, with the purpose of identifying the mechanism(s) by which they influence U. maydis pathogenesis. This investigation involved the creation and functional analysis of a series of U. maydis deletion and expression strains. Together, these findings provided additional knowledge regarding the possible functions of U. maydis asRNAs, and their involvement in controlling important cellular processes, such as carbon metabolism and pathogenesis. Author Keywords: antisense transcripts, fungal carbon metabolism, non-coding RNAs, pathogenesis, Ustilago maydis, xylitol dehydrogenase
Frog Virus 3
Understanding the maintenance and spread of invasive diseases is critical in evaluating threats to biodiversity and how to best minimize their impact, which can by done by monitoring disease occurrences across time and space. I sought to apply existing and upcoming molecular tools to assess fluctuations in both presence and strain variation of frog virus 3 (FV3), a species of Ranavirus, across Canadian waterbodies. I explored the temporal patterns and spatial distribution of ranavirus presence across multiple months and seasons using environmental DNA techniques. Results indicate that ranavirus was present in approximately 72.5% of waterbodies sampled on a fine geographical scale (<10km between sites, 7,150 km2), with higher detection rates in later summer months than earlier. I then explored the sequence variability at the major capsid protein gene (MCP) and putative virulence gene (vIF-2α) of FV3 samples from Ontario, Alberta, and the Northwest Territories, with the premise of understanding pathogen movement across the landscape. However, a lack of genetic diversity was found across regions, likely due to a lack of informative variation at the chosen genetic markers or lack of mutation. Instead, I found a novel FV3-like ranavirus and evidence for a recombinant between FV3 and a ranavirus of another lineage. This thesis provides a deeper understanding into the spatio-temporal distribution of FV3, with an idea of how widespread and threatening ranaviruses are to amphibian diversity. Keywords: ranavirus, frog virus 3, amphibians, environmental DNA, phylogenetics, wildlife disease, disease surveillance, major capsid protein, vIF-2α Author Keywords: amphibians, environmental DNA, frog virus 3, phylogenetics, ranavirus, wildlife disease
Characterizing the demographic history and prion protein gene variation to infer susceptibility to chronic wasting disease in a naïve population of white-tailed deer (Odocoileus virginianus)
Assessments of the adaptive potential of natural populations are essential for understanding and predicting responses to environmental stressors like climate change and infectious disease. The range of stressors species face in a human-dominated landscape, often have contrasting effects. White-tailed deer (Odocoileus virginianus, deer) are expanding in the northern part of their range following decreasing winter severity and increasing forage availability, caused by climate change. Chronic wasting disease (CWD), a prion disease affecting cervids, is likewise expanding and represents a major threat to deer and other cervids We obtained tissue samples from free-ranging deer across their native range in Ontario, Canada which has yet to detect CWD in wild populations of cervids. High throughput sequencing was used to assess neutral genomic variation and variation in the gene responsible for the protein that misfolds into prions when deer contract CWD, known as the PRNP gene. Neutral variation revealed a high number of rare alleles and no population structure, consistent with an expanding population of deer. Functional genetic variation revealed that the frequencies of variants associated to CWD susceptibility and disease progression were evenly distributed across the landscape and the frequencies were consistent with deer populations not infected with CWD. These findings suggest that an observable shift in PRNP allele frequencies likely coincides with the start of a novel CWD epidemic. Sustained surveillance of genomic and genetic variation can be a useful tool for CWD-free regions where deer are managed for ecological and economic benefits. Author Keywords: Canadian wildlife, population genetics, prion, PRNP, RADseq, ungulate
Assessing Molecular and Ecological Differentiation in Wild Carnivores
Wild populations are notoriously difficult to study due to confounding stochastic variables. This thesis tackles two components of investigating wild populations. The first examines the use of niche modeling to quantify macro-scale predator-prey relationships in canid populations across eastern North America, while the second examines range-wide molecular structure in Canada lynx. The goal of the first chapter is to quantify niche characteristics in a Canis hybrid zone of C. lupus, C. lycaon, and C. latrans to better understand the ecological differentiation of these species, and to assess the impacts of incorporating biotic interactions into species distribution models. The goal of the second chapter is to determine if DNA methylation, an epigenetic marker that modifies the structure of DNA, can be used to differentiate populations, and might be a signature of local adaptation. Our results indicated that canids across the hybrid zone in eastern North America exhibit low levels of genetic and ecological differentiation, and that the importance of biotic interactions are largely lost at large spatial scales. We also identified cryptic structure in methylation patterns in Canada lynx populations, which suggest signatures of local adaptation, and indicate the utility of DNA methylation as a marker for investigating adaptive divergence. Author Keywords: Ecological Epigenetics, Ecological Genetics, SDM
Nutrigenomics of Daphnia
Organismal nutrition lies at the interface between biotic and abiotic factors in an ecosystem, dictating the transfer of energy and nutrients across trophic levels. Our ability to detect nutritional limitation in consumers is reliant on a priori knowledge of dietary history due to our inability to differentiate nutrient stress based on body-wide responses. Molecular physiological responses are increasingly being used to measure physiological stress with high levels of specificity due to the specific modes of action ecological stressors have on organismal molecular physiology. Because animal consumers respond to varying nutrient supplies by up- and down-regulating nutrient-specific metabolic pathways, we can quantify nutritional status by quantifying the expression of those pathways. Here I present an investigation into the use of transcriptomics to detect nutritional stress in the keystone aquatic herbivore, Daphnia pulex, I use RNAseq and quantitative PCR (qPCR) identify nutritional indicator genes. I found that nutritional status could be determined with 100% accuracy with just ten genes. Additionally, the functional annotation of those genes uncovered previously unidentified responses to dietary stress. Further testing and validation of the selected indicator genes is required however these findings have the potential to revolutionize our ability to measure and monitor consumer nutritional stress. Author Keywords: Biomarkers, Daphnia, Gene expression, Nutrigenomics, Nutritional ecology, RNAseq
Cytokinin Oxidase/Dehydrogenase (CKX) Gene Family in Soybeans (Glycine max)
Glycine max (soybean) is an economically important plant species that registers a relatively low yield/seed weight compared to other food and oil seed crops due to higher rates of flower and pod abortion. Alleviation of this abortion rate can be achieved by altering the sink strength of the reproductive organs of soybeans. Cytokinin (CK) plays a fundamental role in promoting growth of sink organ (flowers and seeds) by increasing the assimilate demand. Cytokinin oxidase/dehydrogenase (CKX) is an enzyme that catalyses the irreversible breakdown of active CKs and hence reduce the cytokinin content. The current thesis uncovers the members of CKX gene family in soybeans and the natural variations among CKX genes within soybean varieties with different yield characteristics. The identification of null variants of OsCKX2 that resulted in large yield increases by Ashikari et al. (2005) provided a rationale for current thesis. The soybean CKX genes along with the ones from Arabidopsis, Rice and Maize were used to construct a phylogenetic tree. Using comparative phylogeny, protein properties and bioinformatic programs, the potential effect of the identified natural variations on soybean yield was predicted. Five genes among the seventeen soybean CKXs identified, showed polymorphisms. One of the natural variations, A159G, in the gene GmCKX16 occurred close to the active site of the protein and was predicted to affect the activity of enzyme leading to higher accumulation of CKs and hence increased seed weight. Use of such natural variations in marker assisted breeding could lead to the development of higher yielding soybean varieties. Author Keywords: CKX, Cytokinins, Seed weight, Seed Yield, SNPs, Soybeans

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Graduate student theses produced at Trent University. You may also browse theses and dissertations by year, program, or author.

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