Graduate Theses (2019 - present)
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14662/385
This collection contains theses submitted digitally by Mount Allison University graduate students. The option to submit an electronic thesis was introduced in 2019. Electronic theses are required as of the 2025-2026 Academic Calendar.
Some graduate theses published between 2019 and the phasing in of this requirement will only be available in print format. They can be found in the MtA Libraries Catalogue Thesis Collection
Some graduate theses published between 2019 and the phasing in of this requirement will only be available in print format. They can be found in the MtA Libraries Catalogue Thesis Collection
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Item Open Access Legacy contaminants in brook trout from remote New Brunswick lakes(Mount Allison University, 2023-01-03) Fraser, Meghan P.; Kurek, JoshuaDichlorodiphenyltrichloroethane (DDT) and mercury are legacy contaminants that are persistent in the environment for decades or longer. They may impact food webs through bioaccumulation, biomagnification, and chronic toxic effects in exposed biota. DDT was applied aerially on large scales to the conifer forests in north-central New Brunswick between 1952 and 1968 for pest control. I sampled seven lakes in the summers of 2020 and 2021 to investigate the impact of historical DDTs on the present day aquatic environment. I sampled brook trout, aquatic invertebrates, zooplankton, and lake surface sediments. I found DDTs were up to ~14 times higher in brook trout muscle tissues from lakes where DDTs were applied to the watershed compared to reference lakes. DDTs in brook trout exceeded CCME guidelines by up to ~22 times. Mercury is a common contaminant of concern and delivered to lakes by atmospheric transport. Most mercury originates from anthropogenic activities, including burning fossil fuels, and mining or smelting metals rather than natural geogenic sources. I sampled brook trout from seven New Brunswick lakes in 2020, and found mercury levels comparable to similar studies in eastern North America. Mercury in brook trout exceeded CCME guidelines for methylmercury by up to ~12 times. Using DDT and mercury measures, we can further our understanding of legacy contaminants in lakes of New Brunswick, Canada.Item Open Access Prevalence of the zoonotic diseases Leptospirosis and Borreliosis in the Maritimes of Canada(Mount Allison University, 2022) Bishop, Samantha Joyce; Lloyd, VettLeptospirosis and Lyme borreliosis are two globally important infectious diseases caused by the transmission of either the Leptospira spirochaete or the Borrelia spirochaete, respectively. Although the spirochaetes have similarities in their shape, size, and movement, their transmission to animals is quite different. Infection of pathogenic leptospires requires environmental exposure to infected water or soil. The main route of exposure is through mucous membranes, such as drinking from infected water sources. Once infected, some of the leptospires remain in the host’s body and replicate, whereas others pass through the renal tubules to be shed back into the environment through the individual’s urine, continuing the infectious cycle. Borrelia infection, on the other hand, is a tick-borne disease in which an individual becomes infected through the bite of an infected tick. The risk of contracting leptospirosis in Canada has been increasing over the last 30 years, with New Brunswick reporting an increase in infected dogs, an important sentinel species for the infection, with fatal outcomes. To determine the prevalence of Leptospira spp. in the province, multiple methodologies and areas of interest were examined. Three methodologies (centrifugation, filtration, and growth in media) were attempted to detect leptospires in stagnant water sources around areas of recent flooding events. Unfortunately, all three methods returned negative results, although it is unclear if they were unsuccessful in finding the leptospires or if the leptospires were not present in these samples. Molecular testing of local wildlife necropsies, including suspected maintenance hosts as well as accidental hosts, and ticks was carried out. Testing small mammals showed 3.2% specimens were positive for Leptospira borgpetersenii. Testing large mammals showed 1.8% positive for L. borgpetersenii. Infected animals included moose (Alces alces), snowshoe hare (Lepus americanus), meadow vole (Microtus pennsylvanicus), jumping mouse (Napaeozapus insignis), deer mouse (Peromyscus maniculatus), maritime shrew (Sorex maritimensis), and black bear (Ursus americanus). Testing of ticks (Dermacentor variabilis, Ixodes cookei, and Ixodes scapularis) showed 3.6% were positive for L. borgpetersenii. Finally, dog serum was collected from 14 veterinary hospitals across the province with 19.3% testing positive for the presence of antibodies against Leptospira spp. Together, these results elucidate a widespread rate of infection in the wildlife species, sentinel species, and tick species of New Brunswick. The risk of contracting Lyme borreliosis in New Brunswick has also been increasing over the last few years due to expanding tick populations. The risk of transmission of Borrelia species, such B. bissettiae, through the bite of an infected tick within New Brunswick began with the identification of the bacteria in local tick species, yet transmission of B. bissettiae to local wildlife species was still unknown. Of the small wildlife species tested in this study, one meadow vole (M. pennsylvanicus) and one deer mouse (P. maniculatus) were sequence positive for B. bissettiae. Of the large mammals tested, none were positive for the presence of B. bissettiae. This evidence suggests that the bacteria has established maintenance hosts, but evidence for the ability to infect accidental hosts has not yet been found in New Brunswick. Understanding the risk of infection by Borrelia spp. of our local wildlife species becomes directly relevant to human health, as it can cause Lyme disease in humans. In its disseminated form, it can affect organs such as the heart, causing what is known as Lyme carditis, a rare but potentially fatal outcome when diagnoses are missed. This thesis presents a case of fatal severe heart disease following suspected untreated Lyme carditis of a 17-year-old female from Nova Scotia, Canada. Formalin fixed paraffin embedded sections of the heart, lung, kidney, adrenals, and pancreas showed florescent structures through immunohistochemistry staining in similar size and shape of Borrelia bacteria. Due to the nature of these samples, however, these findings could not be confirmed through polymerase chain reaction followed by Sanger sequencing and therefore cannot be confirmed as Borrelia.Item Open Access Reactive oxygen species production and scavenging; genomic patterns across marine phytoplankton(Mount Allison University, 2022-03-30) Omar, Naaman Mahmood Mohamed; Campbell, DouglasMarine phytoplankton produce and scavenge Reactive Oxygen Species (ROS), to maintain intracellular ROS homeostasis to support cellular processes, but limit damaging reactions. Some prokaryotic picophytoplankton have lost genes encoding the capacity to scavenge Hydrogen Peroxide (HO2). The “Black Queen Hypothesis” postulates that prokaryotic picophytoplankton might thereby lower costs through H2O2 diffusing across the membrane of the small source cells. We investigated genomes and transcriptomes from diverse taxonomic lineages of eukaryotic phytoplankton, ranging from 0.4 to 44 µm cell radius, to analyze the fraction of total genes dedicated to producing enzymes metabolizing three distinct ROS. H2O2 has low reactivity, long intracellular and extracellular lifetimes, and readily crosses cell membranes, and can therefore potentially leave a cell before provoking damaging intracellular reactions. Across eukaryotic phytoplankton, the fraction of total genes dedicated to H2O2 production indeed decreases with increasing cell radius, consistent with the maintenance of ROS homeostasis in the face of slower diffusional losses of H2O2. The fraction of total genes dedicated to H2O2 scavenging does not change with increasing cell radius, although taxonomic lineage influences the fraction of total genes dedicated to H2O2 metabolism. Superoxide (O2•−) has high reactivity, short intracellular and extracellular lifetimes and limited membrane permeability. As expected, genes encoding O2•− scavenging were ubiquitous, and did not change with radius, consistent with separate intracellular and extracellular O2•− pools separated by the cell membrane. Nitric Oxide (•NO) has low reactivity, long intracellular and extracellular lifetimes, and readily crosses cell membranes. Neither •NO production nor scavenging genomic capacities changed with increasing cell radius, but were influenced by taxonomic lineage, consistent with the low cytotoxicity and diverse regulatory roles of •NO.Item Open Access Characterizing nutrient-activation of orphan and lipid metabolism-related G protein-coupled receptors(Mount Allison University, 2022-07-11) Power, Madeline Elizabeth; Rourke, JillNutrients and food additives serve as energy sources or non-nutritive flavour enhancers for organisms. Advances in nutrient-sensing mechanisms and the discovery of the reciprocal relationship between metabolism and intracellular pathways have identified some nutritive and non-nutritive food components, namely amino acids (AAs) and non-nutritive sweeteners (NNSs), as ligands for G protein-coupled receptors (GPCRs). For example, AAs act as ligands for mGluRs, multiple class C GPCRs and the class A orphans GPR142 and GPR139. Meanwhile, NNSs of markedly different structures have been shown to activate the sweet taste receptors T1R2/T1R3. The consumption of AAs aids in managing food intake and glucose homeostasis, although the mechanisms underlying these metabolic benefits remain unclear. However, a recent study identified an intestinal trafficking mechanism of individual AAs leading to the activation of an AA-sensing GPCR, suggesting that GPCRs play a larger role in nutrient signalling than once thought. Food products containing NNSs have become increasingly popular over the past few decades to provide powerful sweetness, in part through the activation of the sweet taste receptors T1R2/T1R3, without the added calories. Despite being considered metabolically inert, the consumption of NNSs has been linked to an increased risk of obesity, type 2 diabetes, and metabolic syndrome with suggested off-target signalling through GPCRs independent of T1R2/T1R3. Ligand identification is critical in understanding GPCR function; as a result, we used a high throughput approach quantifying GPCR activation to identify novel nutrient-GPCR interactions. This approach was applied to two experimental questions 1) to what extent do AAs activate orphan and lipid metabolism-related GPCRs, and 2) do NNSs elicit off-target signalling events through interactions with GPCRs? Both projects primarily measured b-arrestin recruitment and used a panel of in vitro luciferase signalling reporters. Herein, we discovered that the AA L-phenylalanine (Phe) is a promiscuous endogenous ligand, significantly activating 148 class A GPCRs. Additionally, we found that the NNS sucralose increases the activity of the constitutively active orphan GPCR GPR52. These observations are the first to identify the widespread binding capacity of Phe through GPCRs and a GPCR other than the taste receptors as a target for sucralose. This study provides evidence of the interplay between metabolite sensing and the GPCR signalling network and may potentially inform pharmacological approaches to predict novel agonists or off-target effects.Item Open Access Molecular testing of Lyme disease(Mount Allison University, 2020-09) Haque, Md. Hasibul; Lloyd, VettLyme disease is a tick-vectored multisystemic illness caused by the bacteria Borrelia burgdorferi sensu lato contracted throughout North America and Eurasia. Although Lyme disease is the most common tick vectored illness in North America, many questions about the disease such as pathophysiology and organ involvement remained unresolved. Additionally, persistence of the Borrelia bacteria after antibiotic treatment is controversial and the role of antibiotic tolerant bacteria in causing chronic Lyme disease symptoms is even less well understood. The reliance on serological testing in Lyme disease leaves many questions unanswered and accurate diagnosis of Lyme disease in certain situations is challenging. To address some of these outstanding questions, direct detection of Borrelia from biopsy and autopsy tissue and culturing of Borrelia from patients showing persistent Lyme disease symptoms can be valuable. In this study, I investigated autopsy tissues using the DNA-based detection methods of nested PCR and Fluorescent in situ hybridization (FISH) and the protein-based technique of immunohistology from seropositive, seronegative, and serologically untested individuals. This study showed that Borrelia was widely distributed in different organs in both seropositive and seronegative participants. These techniques were then extended to biopsy tissue samples. My findings showed that B. burgdorferi is pleiomorphic, with FISH and immunohistology showing predominantly round body and biofilm forms with fewer in the spirochetal form. Finally, I showed that culture of viable Borrelia is possible from different body fluids from participants with persistent Lyme disease symptoms. This finding strengthens the evidence that chronic Lyme disease is associated with an active and long-standing Borrelia infection. Findings from this study could be extended to investigation of other tick-vectored diseases and reinforce the potential for the use of direct molecular methods in disease diagnosis.Item Open Access Using multi-proxy measures of lake sediments to identify environmental changes in protected watersheds of British Columbia, Canada(Mount Allison University, 2023-01-03) Di Lonardo, Alexandra; Kurek, JoshuaPaleolimnology uses lake sediments to recognize environmental trends through time. This is useful in watersheds with a knowledge gap of historical environmental conditions or missing perspectives of long-term ecosystem responses. Cameron Lake sediments were used to identify historical trends of Didymosphenia geminata valves in a mat-prone watershed. The lake core represented approximately 600 years of sediment accumulation and findings demonstrated that D. geminata was a historical member of the riverine diatom community. Though in low abundance in older sediment, valve concentrations increased in the early 1900s and peaked at ~1990s, coinciding with observations of mats. Geochemical proxy measures were then analyzed to explore if watershed disturbance was a driver of environmental conditions favouring D. geminata mat formation. No clear geochemical trends were identified, thus watershed disturbance was not associated with D. geminata proliferation in the ~600 year record. Cultus Lake has experienced urbanization, resulting in cultural eutrophication. Over the past century, water quality metrics suggested a decline in hypolimnetic oxygen, however there is a lack of temporal knowledge on the biological responses to eutrophication. Cultus Lake sediments were analyzed for temporal trends in benthic invertebrate assemblages. Chironomid assemblages shifted from taxa associated with oligotrophic, high oxygen conditions to an assemblage indicative of low oxygen conditions. This shift began in the 1920s, coinciding with forestry and agricultural activities. A recent assemblage shift in the 1970s indicated that the assemblage is now dominated by generalist taxa. Findings suggest the benthic environment of Cultus Lake has less oxygen availability in recent decades. This temporal information can be used in future lake management and recovery plans for species of concern at Cultus Lake.Item Open Access Influence of diel thermal variability on growth, development, swimming performance and stress response in salmonid fishes(Mount Allison University, 2022-08) Andrew, Sean; Morash, AndreaAccurately understanding the biological effects of temperature is important for effective species conservation, especially in this era of climate warming. Traditionally, temperature effects on fishes have been understood using fish held at stable temperatures. In many natural freshwater fish habitats, however, water temperature cycles daily. Diel thermal cycles can be as wide as 5-9 C in key salmonid habitats like the Miramichi River in New Brunswick. To date, little is known about the biological effects of diel thermal cycles on fishes. In my thesis, I investigated the growth, development, and swimming performance of Atlantic salmon (Salmo salar) under 16-21 and 19-24 C diel thermal cycles (representing cool and warm sites in the summer at the Miramichi). Additionally, I examined the stress response and post-angling survival of brook trout (Salvelinus fontinalis) after exposure to diel cycles with different daily thermal maximums (24, 26, or 27 C). I found that Atlantic salmon grew at similar rates at 16-21 and 19-24 C as parr, but smolts grew slower at 19-24 C especially for those from the relatively cooler Restigouche river compared to those from Miramichi. Atlantic salmon swimming efficiency was insensitive to acute warming or acclimation thermal cycle while sustainable swimming capacity stayed >90% (of the maximum) at the warmest test temperature (24 C) for both acclimation groups. Overall, Atlantic salmon appeared more resilient to warm temperatures than thought based on stable temperature experiments. Brook trout increased metabolic rate above resting levels after 26 or 27 C exposure which also increased some reflex impairments predicting greater postangling mortality. Tmax may be an important factor to consider in future closing/opening of recreational fisheries which currently considers some other water temperature parameter.