Dorken, Marcel

Advanced generation/backcrossed (non-F1) hybrids can be challenging to identify when their traits are similar to those of parental taxa, F1 hybrids, or both. This is particularly evident in the North American hybrid zone involving Typha latifolia, T. angustifolia, F1 T. × glauca and non-F1 hybrids. Cattails are challenging to differentiate based on gross morphological characteristics. Microscopic characteristics in female inflorescences have not been previously studied to differentiate parental taxa from non-F1 hybrids. To investigate whether researchers can use microscopic floret and bracteole characteristics for taxonomic identification, I compared pistillate flower length, bracteole length and width, and bracteole colour among taxa. I found that floret and bracteole characteristics can be useful for identifying T. latifolia but cannot accurately differentiate T. angustifolia and F1 T. × glauca from non-F1 hybrids. Further, a flowering bias can lead to the underestimation of the frequency of T. latifolia when using floral characters to examine the relative abundance of cattail taxa.

Author Keywords: advanced-generation hybrids, backcrossed hybrids, invasive species, morphology, species identification, Typha spp.

Wetlands are highly susceptible to the invasion of invasive species. The invasive hybrid cattail (Typha × glauca) is prevalent in the southeastern Prairie Pothole Region (PPR) wetlands. However, concerns arise about its recent proliferation in the northwestern PPR without maternal T. angustifolia. To determine taxonomic distribution, I used species-specific PCR-RFLP and microsatellite markers for genotyping 245 samples from 50 northwest PPR sites. I found 75% T. latifolia, 7% T. angustifolia, 16% T. × glauca, and 2% backcrossed or advanced-generation hybrids. F1 T. × glauca has expanded in western PPR without its mother species, and the low occurrence of later-generation hybrids indicates their recent range expansion. Additionally, T. angustifolia offspring make fewer hybrids, which suggests that reproductive barriers may limit hybridization between parental species. This study highlights the vulnerability of prairies to cryptic invasions by Typha hybrids, and early detection of invasive species is a critical factor in wetland management success.

Increased plant size is expected to have negative consequences for mating by increasing pollen transfer among the same plant. However, recent theoretical studies have demonstrated that this may not be true for clonal plants. Instead, clonal expansion could enhance outcrossing opportunities without increasing selfing by reducing distances to potential mates. I investigated how the spatial structure of clones influences patterns of pollen dispersal, selfing rates and siring success in a natural population of Sagittaria latifolia. I found that pollen dispersal distances typically exceeded the spatial extent of clones and there was a positive association between clone size and the likelihood that clones were intermingled. Together, this resulted in a weak positive association between clone size and selfing rates, and a strong positive association between clone size and outcross siring success. This is the first empirical support for the theoretical expectation that any negative effects of selfing in large clones might be offset by increased siring success.

Author Keywords: clonal growth, fitness gain curve, geitonogamy, plant mating, plant reproductive ecology, sex allocation theory

The cost of reproduction refers to the use of resources for the production of offspring that decreases the availability of resources for future reproductive events and other biological processes. Models of sex-allocation provide insights into optimal patterns of resource investment in male and female sex functions and have been extended to include other components of the life history, enabling assessment of the costs of reproduction. These models have shown that, in general, costs of reproduction through female function should usually exceed costs through male function. However, those previous models only considered allocations from a single pool of shared resources. Recent studies have indicated that the type of resource currency can differ for female and male sex functions, and that this might affect costs of reproduction via effects on other components of the life history. Using multiple invasibility analysis, this study examined resource allocation to male and female sex functions, while simultaneously considering allocations to survival and growth. Allocation patterns were modelled using both shared and separate resource pools. Under shared resources, allocation patterns to male and female sex function followed the results of earlier models. When resource pools were separate, however, allocations to male function often exceeded allocations to female function, even if fitness gains increased less strongly with investment in male function than with investment in female function. These results demonstrate that the costs of reproduction are affected by (1) the types of resources needed for reproduction via female or male function and (2) via trade-offs with other components of the life history. Future studies of the costs of reproduction should examine whether allocations to reproduction via female versus male function usually entail the use of different types of resources.

Author Keywords: Cost of Reproduction, Gain Curve, Life History, Resource Allocation Patterns, Resource Currencies

Competition is known to impact population dynamics through both indirect and direct interactions, and direct interactions can often lead to injury in one or both parties. As such, response to injury through tissue regeneration can be important for surviving post-competitive interaction. However, the impacts of outside factors like temperature and genome size (e.g. polyploidy) are not well studied, especially in syntopic systems. We addressed this knowledge gap by comparing regeneration rates of diploid Ambystoma laterale and triploid unisexual Ambystoma at two ecologically-relevant temperatures. Environmental factors appeared to have stronger effects on regeneration than ploidy level, but overall mass was impacted more strongly by ploidy level. Interestingly, there was an interaction between temperature and time within unisexuals that was absent when comparing different ploidy levels, implying temperature has a more complex effect on polyploids. This study supports the hypothesis that polyploid organisms are better equipped to respond to shifts in their environments, which can give them a competitive advantage at the northern range limit of this species complex.

Author Keywords: Ambystoma, Genome dosage, Hybrid vigor, Polyploidy, Thermal optimum, Tissue regeneration

In Canada, eastern flowering dogwood (Cornus florida L.) is an endangered tree that occurs only in the Carolinian forest of southern Ontario. Threats to this species include habitat fragmentation and the fungal pathogen dogwood anthracnose (Discula destructiva). I conducted a population genetic analysis using seven nuclear microsatellite markers to determine if fragmented populations are genetically isolated from one another and have low levels of genetic diversity. Genetic comparisons suggest on-going dispersal among sites and relatively high genetic diversity within most sites; however, smaller populations and younger trees were less genetically diverse. I also used linear mixed effects models to assess potential relationships between several ecological variables and the prevalence of dogwood anthracnose. Disease severity was higher in trees on shallow slopes and in larger trees; the latter also had higher likelihood of infection. Insights from this study will be important to incorporate into future management strategies.

Author Keywords: Cornus florida, Discula destructiva, dogwood anthracnose, Eastern flowering dogwood, endangered, population genetics

According to the Invasional Meltdown Hypothesis (IMH), invasive species may interact in their introduced range and facilitate future invasions. This study investigated the possibility that Alliaria petiolata, an invasive allelopathic herbaceous plant in Ontario, is facilitating invasions by additional alien species. Two allelopathic focal species were chosen for this study: the native Solidago canadensis and the invasive A. petiolata. Field surveys in southern Ontario that quantified plant biodiversity in plots that included one or both focal species revealed no support for the IMH, although fewer species co-existed with A. petiolata than with S. canadensis. A year-long recruitment experiment in Peterborough, Ontario, also produced results inconsistent with the IMH, although did provide some evidence that A. petiolata limited recruitment of other species. These results collectively show negative impacts on regional biodiversity by A. petiolata, even in the absence of an invasional meltdown.

Author Keywords: allelopathy, Alliaria petiolata, co-occurrence surveys, invasional meltdown hypothesis, invasive species, Solidago canadensis

Interspecific hybridization is an important evolutionary process which can contribute to the invasiveness of species complexes. In this dissertation I used the hybridizing species complex of cattails (Typha spp., Typhaceae) to explore some of the processes that could contribute to hybridization rates. Cattails in northeastern North America comprise the native T. latifolia, the non-native T. angustifolia, and their fertile hybrid, T. × glauca. First, I examined whether these taxa segregate by water depth as habitat segregation may be associated with lower incidence of hybridization. I found that these taxa occupy similar water depths and therefore that habitat segregation by water depth does not promote mating isolation among these taxa. I then compared pollen dispersal patterns between progenitor species as pollen dispersal can also influence rates of hybrid formation. Each progenitor exhibits localized pollen dispersal, and the maternal parent of first generation hybrids captures more conspecific than heterospecific pollen; both of which should lead to reduced hybrid formation. I then conducted controlled crosses using all three Typha taxa to quantify hybrid fertility and to parameterize a fertility model to predict how mating compatibilities should affect the composition of cattail stands. I found that highly asymmetric formation of hybrids and backcrosses and reduced hybrid fertility should favour the maintenance of T. latifolia under certain conditions. Finally, I used a population genetics approach to characterize genetic diversity and structure of Typha in northeastern North America to determine the extent to which broad-scale processes such as gene flow influence site-level processes. I concluded that hybrids are most often created within sites or introduced in small numbers rather than exhibiting broad-scale dispersal. This suggests that local processes are more important drivers of hybrid success than landscape-scale processes which would be expected to limit the spread of the hybrid. Though my findings indicate some barriers to hybridization in these Typha taxa, hybrid cattail dominates much of northeastern North America. My results therefore show that incomplete barriers to hybridization may not be sufficient to prevent the continued dominance of hybrids and that active management of invasive hybrids may be required to limit their spread.

Author Keywords: fertility model, genetic structure, Hybridization, invasive species, niche segregation, pollen dispersal

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