Graduate Theses & Dissertations

Pages

role of Cln5 in autophagy, using a Dictyostelium discoideum model of Batten disease
This thesis investigated the role of the neuronal ceroid lipofuscinosis protein, Cln5, during autophagy. This was accomplished by performing well-established assays in a Dictyostelium cln5 knockout model (cln5-). In this study, cln5- cells displayed a reduced maximum cell density during growth and impaired cell proliferation in autophagy-stimulating media. cln5- cells had an increased number of autophagic puncta (autophagosomes and lysosomes), suggesting that autophagy is induced when cln5 is absent. cln5- cells displayed increased amounts of ubiquitin-positive proteins but had no change in proteasome protein abundance. During the development of cln5- cells, fruiting bodies developed precociously and cln5- slug size was reduced. Lastly, when cln5- cells were developed on water agar containing ammonium chloride (NH4Cl), a lysosomotropic agent, the formation of multicellular structures was impaired, and the small slug phenotype was exaggerated. In summary, these results indicate that Cln5 plays a role in autophagy in Dictyostelium. The cellular processes that regulate autophagy in Dictyostelium are similar to those that regulate the process in mammalian cells. Thus, this research provides insight into the undefined pathological mechanism of CLN5 disease and could identify cellular pathways for targeted therapeutics. Author Keywords: Autophagy, Batten disease, Cln5, Dictyostelium discoideum, NCL
Using DNA Barcoding to Investigate the Diet and Food Supply of a Declining Aerial Insectivote, the Barn Swallow (Hirundo rustica)
Barn Swallow (Hirundo rustica) populations have declined in North America over the past 40 years and they are listed as Threatened in Ontario, Canada. Changes in the food supply have been hypothesized as a potential cause of this population decline. I used DNA barcoding to investigate the diet and food supply of Barn Swallows and to determine if the food supply affects their reproductive performance. In two breeding seasons, I monitored nests, collected fecal samples, and monitored prey availability by collecting insects from the habitat surrounding breeding sites using Malaise traps. I used DNA barcoding to identify insect specimens collected from the habitat and to identify prey items from Barn Swallow nestling fecal samples. I found that Barn Swallow nestlings were fed a very broad range of prey items but were fed larger prey items more frequently. Prey availability was not related to the timing of reproduction, the number of nests at a breeding site, or the reproductive output of individual nests. This study provides information on the diet composition of Barn Swallows in North America and suggests that food limitation during the breeding season may not be a major factor in their population decline. Author Keywords: aerial insectivore, diet, DNA barcoding, Hirundo rustica, metabarcoding, reproductive success
Understanding the establishment of Typha spp. in North America using population genetics and common garden studies
There are three cattail (Typha) taxa in Canada: T. latifolia (native), T. angustifolia (introduced), and their hybrid T. x glauca. The latter is invasive in regions around the Laurentian Great Lakes, and I investigated the potential role that commercial suppliers may be playing in the introduction of non-native Typha by comparing genotypes of North American, European, and commercially available plants. I found that Ontario garden centres are importing both hybrids and non-native lineages of T. angustifolia into Canada, but was unable to identify the provenance of T. latifolia. I also investigated the possibility that the hybrid cattail leaf litter shade and leachate influences germination and early growth of the parental species of the hybrids. Using three common garden experiments, I found that T. x glauca leaf litter suppresses germination rates of the three taxa. In the early seedling growth experiment, plant performance varied by taxa, and for the competition experiment there were no intra- or interspecific competition or treatment effects on the performance of plants. Overall, my research identified a potential mechanism allowing T. x glauca to dominate wetlands, and also shows that non-native lineages are being introduced into Canada through commercial trade Author Keywords: Competition, Germination, Non-native lineages, Plant nurseries, Seedling Growth, Typha spp.
Time-dependent effects of predation risk on stressor reactivity and growth in developing larval anurans (Lithobates pipiens)
The predator vs. prey dynamic is an omnipresent factor in ecological systems that may drive changes in life history patterns in prey animals through behavioural, morphological, and physiological changes. Predation risk can have profound effects on the life history events of an animal, and is influenced by the neuroendocrine stress response. Activation of the hypothalamic-pituitary-adrenal/interrenal axis, and the induction of stress hormones (e.g., corticosterone (CORT)) have been shown to mediate the onset of inducible anti-predator defensive traits including increased tail-depth, and reduced activity. The predator-prey relationship between dragonfly nymphs and tadpoles can be a powerful model system for understanding mechanisms that facilitate changes in the stress response in accordance with altered severity of risk. It has been well demonstrated early in tadpole ontogeny that increased corticosterone (CORT) levels, observed within three weeks of predator exposure, are correlated with increased tail depth morphology. However, the reactivity of the stress response in relation to the growth modulation in developing prey has yet to be fully explored. Accordingly, this thesis assessed the stress and growth response processes in tadpoles that were continuously exposed to perceived predation risk later in ontogeny. Continuous exposure of prey to predation risk for three weeks significantly increased CORT levels, and tail depth. However, tadpoles exposed to six weeks of predation risk acclimated to the presence of the predator, which was observed as a significant reduction of stressor-induced CORT levels. In addition, although increased tail depth has been attributed to predator defense, predator-naïve tadpoles began to display similar tail depth morphology as treated tadpoles at the six week time point. Thus, this thesis suggests that the stress response in lower vertebrate systems (e.g., tadpoles) may operate in a similarly complex manner to that observed in higher vertebrates (e.g., rats), for which severity of risk associated with the stressor aids in defining activity of the stress response. Moreover, the lack of morphological difference between treatments among tadpoles exposed later in ontogeny suggests that the mechanisms for inducing defenses are normal morphological traits in the development of the animal. This thesis paves the way for future research to elucidate the relationship between the neuroendocrine stress response and hormonal pathways involved in growth modulation in the presence of environmental pressures. Author Keywords: Acclimation, Corticosterone, Growth Modulation, Predation Risk, R. pipiens, Tadpole
Tests of the Invasional Meltdown Hypothesis in invasive herbaceous plant species in southern Ontario
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
Syrphidae (Diptera) of northern Ontario and Akimiski Island, Nunavut
Syrphids, also known as hover flies (Diptera: Syrphidae) are a diverse and widespread family of flies. Here, I report on their distributions from a previously understudied region, the far north of Ontario, as well as Akimiski Island, Nunavut. I used samples collected through a variety of projects to update known range and provincial records for over a hundred species, bringing into clearer focus the distribution of syrphids throughout this region. I also analysed a previously un-tested trap type for collecting syrphids (Nzi trap), and report on results of DNA analysis for a handful of individuals, which yielded a potential new species. Author Keywords: Diptera, Ontario, range extension, Syrphidae
Social discrimination by female polar bears (Ursus maritimus) when accompanied by dependent offspring during the ice-free season in southern and western Hudson Bay and James Bay
Polar bears are generally described as solitary, but features of their life cycles and habitats regularly necessitate interaction. Effective conspecific assessment, including accurate recognition and discrimination, likely confers benefits, especially to females accompanied by dependent young. Individuals in the Southern (SH) and Western (WH) Hudson Bay subpopulations are ideal for studying polar bear social behaviours because of the prolonged high densities of the ice-free season. First, I looked outside family groups to model their fine scale sociospatial organization on land. Capture locations were more likely to correspond to family groups when there were fewer neighbouring bears, when a greater proportion of neighbours were female, and when the focal individual and neighbours were significantly related. Second, I looked within the family group to assess offspring recognition. Of 288 offspring in 207 family groups captured in the SH subpopulation from 1999 through 2013, only one case of adoption (of a singleton) was observed. Author Keywords: Adoption, Kin Recognition, Logistic Regression, Maternity Analysis, Social Discrimination, Sociospatial
Selection on functional genes across a flying squirrel (genus Glaucomys) hybrid zone
While hybridization between distinct taxa can have undesirable implications, it can also result in increased genetic variability and potentially, the exchange of adaptive genes or traits. Adaptive variation acquired through introgressive hybridization may be particularly advantageous for species facing rapid environmental change. I investigated a novel, climate change-induced hybrid zone between two flying squirrel species: the southern (Glaucomys volans) and northern (G. sabrinus) flying squirrel. I was interested in the occurrence of hybridization and introgression, the type of selective pressures maintaining the hybrid zone and the potential for adaptive introgression. I found relatively low hybridization and introgression frequencies (1.7% and 2.9% of the population, respectively) and no evidence of selection on hybrids or backcrosses in particular environments. I conclude that the data are more consistent with a hybrid zone maintained by endogenous (environment-independent) selection. I tested for adaptive introgression using two functional genes: IGF-1 and CLOCK. I documented intermediate functional allele frequencies in backcrosses compared to parental populations, suggesting the alleles do not confer fitness advantages in backcrosses. Despite lack of evidence for current adaptive introgression, genetic admixture between G. volans and G. sabrinus may provide adaptive potential should these species face more rapid or drastic environmental change in the future. Author Keywords: adaptive introgression, flying squirrel, Glaucomys sabrinus, Glaucomys volans, hybridization, introgression
Scarring, sex assignment, and sex-specific sociality of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary and eastern Taiwan Strait
The Pearl River Estuary (PRE) and eastern Taiwan Strait (ETS) populations of Indo-Pacific humpback dolphins (Sousa chinensis) contain ~600 and 100 catalogued individuals, respectively. Population demography is important for conservation actions but few animals have been sexed by conventional methods. Longitudinal analysis of tooth-rake scars on dorsal fins showed scars disappear within 7 months; sexing adults by scarring is likely not impacted by juvenile scarring. Using dorsal fin photographs, sex assigned for 87% of catalogued PRE adults (n=300) and for 93% of ETS adults (n=60), using scars hypothesized from male-male competition, was in concordance with sex assigned by DNA, calf association, and ventral photographs. Scarring was higher in presumed males than females and in PRE females than ETS females. Female:male sex ratios were 3:2 (PRE) and 2:1 (ETS), though this likely results from biases in photo-identification methods. Social analysis with presumed sexes showed strong female-female associations in both populations but stronger female-male and male-male associations in PRE. These results support sex differentiation by scarring, which was a non-invasive approach, and sex assignment for many PRE and ETS individuals. Author Keywords: Indo-Pacific humpback dolphins, photo-identification, scarring, sex differentiation, sexes, social structure
Population Dynamics of Eastern Coyotes in Southeastern Ontario
The ability of animal populations to compensate for harvest mortality provides the basis for sustainable harvesting. Coyote populations are resilient to exploitation, but the underlying mechanisms of compensation and how they inter-relate are not fully understood. Moreover, deficiencies in the quality and quantity of information about eastern coyotes preclude effective management. I combined field work, laboratory work, and genetic profiling to investigate the population dynamics of eastern coyotes in southeastern Ontario. Specifically, I conducted research on coyotes during 2010–2013 in Prince Edward County where coyote hunting and trapping seasons were open all year. First, I investigated their social status dynamics and space-use patterns. Transients exhibited extensive space-use relative to residents, potentially encountering vacant territories and/or breeding positions, and some transients became residents, potentially filling vacant territories and/or breeding positions. Accordingly, the study population demonstrated the potential to compensate for harvest mortality via source-sink dynamics and/or buffering reproductive capacity. Second, I investigated their survival and cause-specific mortality. Residents exhibited greater survival than transients, probably partly because of the benefits of holding a territory, and transients seemingly exhibited greater vulnerability to harvest than residents, probably partly because their movements exposed them to greater cumulative mortality risks over time. Accordingly, harvest mortality disproportionately impacted the non-reproductive segment of the study population and thus may have failed to substantially limit reproduction, and thus recruitment. Third, I investigated their reproduction and breeding histories. Females in the study population exhibited age-specific reproductive rates and litter sizes generally typical of those in exploited coyote populations. Accordingly, increased reproductive rates and increased litter sizes may have offset losses due to harvest mortality. There was at least some breeder turnover in the study population due to harvest mortality, but many breeders survived to reproduce for multiple years and those that died were quickly replaced. My findings have important management implications for eastern coyotes and contribute significantly to better understanding of their resilience to harvest. Indiscriminate killing of coyotes through liberal harvest is unlikely to be effective in reducing their abundance. Management strategies should consider non-lethal alternatives and/or targeted lethal control for dealing with problem coyotes. Author Keywords: Canis latrans var., eastern coyotes, population dynamics, Prince Edward County, southeastern Ontario
Phytohormone-enhanced heavy metal responses in Euglena gracilis
Phytohormones, Cytokinin (CK) and Abscisic acid (ABA), are best known for controlling plant growth and stress responses; but they also mediate various developmental perspectives in alga. Yet, their mode of action in algal adaptive strategies to heavy metal responses, their involvement in orchestration of phytohormone crosstalk remain largely unknown and a molecular framework of phytohormone-controlled heavy metal uptake is absent. I found that three metals known globally to contaminate aquatic ecosystems, nickel (Ni), lead (Pb), and cadmium (Cd), cause changes in the levels of endogenous CKs, ABA, auxins, and gibberellins (GAs) in the green alga Euglena gracilis. Exogenous ABA or CK (trans-zeatin) alleviated metal toxicity through improved metal uptake efficiency and the regulation of the endogenous CKs activity profiles and GAs activity. This new evidence suggests that E. gracilis possesses functional phytohormone signals and metabolic pathways that are under metal stress response. Exogenously applied ABA or CK provoked the coordinated activation of metal uptake, likely via enhanced accumulation of metal binding compounds (i.e., proline, glycine, cysteine containing peptides), which are effective for metal sequestration. Using untargeted metabolomics analysis and functional annotation, this thesis further established that, CK and ABA modified pathways and metabolites, which were mainly involved in metal acclimation and resistance. These modified metabolites that were under the influence of phytohormones in algal cells growing under metal stress conditions were associated with: lipid pathways, riboflavin metabolism, biosynthesis of cofactors/vitamin, and carbohydrate metabolism. Bioactive secondary compounds (e.g., terpenoids, alkaloids, flavonoids, carotenoids) were also modified in algal cells treated with phytohormones. The present study highlights that ABA and CKs are important regulators of algal metal accumulation/acclimation strategies based on increased metal uptake, enhanced CK metabolism, regulation of hormonal crosstalk and regulation of some core cellular metabolism pathways, all of which improve metal uptake efficiency. Finally, our results suggest that ABA and CK form a novel strategy for metal bioremediation techniques and for sourcing microalgal value-added metabolites. Author Keywords: abscisic acid, cadmium, cytokinin, Euglena gracilis, lead, nickel
Mutation of the B10 Tyrosine and E11 Leucine in Giardia intestinalis Flavohemoglobin
The flavohemoglobin in Giardia intestinalis (gFlHb) is the only known protozoan member of a protein class typically associated with detoxifying nitric oxide (by oxidation to nitrate) in bacteria and yeast. Mutants of the B10 tyrosine (Y30F) and E11 leucine (L58A), conserved residues thought to influence ligand binding, were expressed and studied using Resonance Raman (RR) spectroscopy. In the wild type protein, RR conducted using a carbon monoxide probe detects two distinct Fe-CO stretches associated with two different active site configurations. In the open configuration, CO does not interact with any polar side chains, while in the closed configuration, CO strongly interacts with one or more distal residues. Analysis of the Y30F mutant provided direct evidence of this tyrosine’s role in ligand stabilization, as it had only a single Fe-CO stretching mode. This stretching mode was higher in energy than the open conformer of the wild type, indicating a residual hydrogen bonding interaction, likely provided by the E7 glutamine (Q54). In contrast the L58A mutant had no effect on the configurational nature of the enzyme. This was unexpected, as the side chain of L58 sits atop the heme and is thought to regulate the access of distal residues to the heme-bound ligand. The similar spectroscopic properties of wild type and L58A suggest that any such regulation would involve rapid conformational dynamics within the heme pocket. Author Keywords: B10 Tyrosine, Catalytic Globin, E11 Leucine, Flavohemoglobin, gFlHb, Giardia intestinalis

Pages

Description

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

In collections

Search Our Digital Collections

Query

Enabled Filters

  • (-) ≠ Nocera
  • (-) = Environmental and Life Sciences
  • (-) ≠ Ecology
  • (-) = Biology

Filter Results

Date

2004 - 2024
(decades)
Specify date range: Show
Format: 2024/04/16

Collection

Author Name

Show more

Name (Any)

Show more

Degree

Subject (Topic)

Show more