Dorken, Marcel

Puccinia triticina, wheat leaf rust (WLR), is the most economically damaging fungal rust of wheat on a global scale. This study identified transcriptome changes in a recently emerged race of WLR in Ontario with a new virulence type relative to a possible ancestor race. Also, this study focused on detecting variation in candidate virulence genes and uncovering novel insight into WLR virulence evolution. Various race-by-variety interactions were evaluated using RNA-seq experiments. A list of genes with statistically significant expression changes in each comparison was prepared and predicted effectors were retained for further analysis. Proteins with nonsynonymous substitutions were run through BLASTx to identify potential orthologs. Over 100 candidate effectors with a 2-fold or higher change in transcript level were identified. Seven of these candidate effector genes were recognized to contain single nucleotide polymorphisms (SNPs) which altered the amino acid sequence of the resulting protein. The information gained may aid in targeted breeding programs to combat new WLR races as well as provide the basis for functional analysis of WLR using potential orthologs in a model basidiomycete.

Author Keywords: effectors, RNA-seq, rust fungi, SNPs, transcriptome, wheat leaf rust

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

Decomposition of aquatic macrophytes has an important role in defining lake carbon (C) storage and nutrient dynamics. To test how diversity impacts decomposition dynamics and site-quality effects, I first examined whether the decomposition rate of aquatic macrophytes varies with species richness. Generally, I found neutral effects of mixing, with initial stoichiometry of component species driving decomposition rates. Additionally, external lake conditions can also influence decomposition dynamics. Therefore, I assessed how the decomposition rate of a submersed macrophyte varies across a nutrient gradient in nine lakes. I found decomposition rates varied among lakes. Across all lakes, I found Myriophyllum decomposition rates and changes in stoichiometry to be related to both nutrients and water chemistry. During the incubation changes in detrital stoichiometry were related to lake P and decomposition rates. Aquatic plant community composition and stoichiometry could alter decomposition dynamics in moderately nutrient enriched lakes.

Author Keywords: Aquatic Plants, Decomposition, Diversity, Littoral, Macrophytes, Nutrients

Magnolia acuminata (Cucumber tree) is the only native Magnolia in Canada, where it is both federally and provincially listed as endangered.Magnolia acuminata in Canada can be found inhabiting pockets of Carolinian forest within Norfolk and Niagara regions of southwestern Ontario. Using a combination of nuclear and chloroplast markers, this study assessed the genetic diversity and differentiation of M. acuminata in Canada, compared to samples from the core distribution of this species across the United States. Analyses revealed evidence of barriers to dispersal and gene flow among Ontario populations, although genetic diversity remains high and is in fact comparable to levels of diversity estimated across the much broader range of M. acuminata in the USA. When examining temporal differences in genetic diversity, our study found that seedlings were far fewer than mature trees in Ontario, and in one site in particular, diversity was lower in seedlings than that of the adult trees. This study raises concern regarding the future viability of M. acuminata in Ontario, and conservation managers should factor in the need to maintain genetic diversity in young trees for the long-term sustainability of M. acuminata in Ontario.

Author Keywords: conservation genetics, cpDNA, forest fragmentation, Magnolia acuminata, microsatellites, population genetic structure