Department of Biology Graduate Theses
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Item Understanding likely responses of a low Arctic mesic tundra plant community to anticipated climate warming using long-term, climatically realistic soil nutrient enhancements(2025-01-10) Wood, Dominic Anthony; Biology; Grogan, PaulTundra plant community composition and structure will be directly influenced by the particularly rapid climate warming currently occurring in the Arctic. Furthermore, increased soil microbial activity due to warming will enhance the supply of growth-limiting nutrients to plants and therefore influence plant community composition. In recent decades, vegetation composition has been shifting in many locations across the Low Arctic and shrubs are expanding their cover and range. Tundra greening and the associated reduction in albedo (reflectance) as well as the potential for widespread soil carbon losses to the atmosphere are expected to cause significant positive feedbacks to warming. Currently, we have a limited understanding of these feedbacks – and particularly of how climatically realistic increases in soil fertility will impact vegetation. Experimental warming significantly increased deciduous and evergreen shrub biomass after 14 years at the low Arctic Daring Lake site, and experiments with factorial large additions of nitrogen and phosphorus eliminating nutrient limitation have increased deciduous shrub growth there and at several other Arctic sites. While these high-level additions demonstrated species’ nutrient limitation regimes and established a dogma of nitrogen-limited plant growth in the tundra, they typically enhance soil nutrient availability far above expected what is expected with climate warming over coming decades. In this study, plant community aboveground biomass, and shoot growth measurements of Betula glandulosa were measured after 19 and 18 years, respectively, of factorial annual low-level nitrogen and phosphorus additions to simulate climatically realistic anticipated increases in soil fertility Corroborating results from high-level fertilization experiments, the low nitrogen addition significantly influenced some individual species’ biomass, and community composition. Furthermore, soil active layer depth was significantly correlated with community composition, positively with some species and negatively with others, suggesting an additional mechanism by which warming may significantly influence tundra plant communities. Finally, only birch shoot growth measurements from the sampling year corroborated known NP growth colimitation. Together, these responses to low-level factorial N x P additions improve our understanding of likely plant community shifts in response to future climate warming, and suggest scalar issues are critical, often overlooked factors needed to accurately predict patterns of future plant community change.Item Do urban environments ameliorate range-limiting challenges for urban-tolerant species?(2024-12-23) Petrenko, Julianna Azaria; Biology; Bonier, Frances; Martin, PaulSpecies’ distributions are constrained by challenges which usually increase in severity approaching the range edge. While urban environments might generally be expected to exacerbate such range-limiting challenges, some urban-tolerant species take advantage of the opportunities provided by cities and persist in urban areas. For these urban-tolerant species, cities might ameliorate range-limiting challenges; however, no direct tests of this hypothesis exist. To test how urban environments affect urban-tolerant species’ distributions, I compared the relative abundance of North American, urban-tolerant birds (N = 42 species) across their distributions in both urban and nonurban habitats. I used data from the eBird Status & Trends Products and a novel measure, the population lethal dose (PLD), to quantify the decline in relative abundance of each species approaching geographic and climatic range edges, in both urban and nonurban habitat. Results suggest that urban environments often ameliorate range-limiting challenges. I found evidence of varying degrees of amelioration at the geographic, dry, and cold range edges, exacerbation and amelioration at the warm range edge, depending on the species’ degree of urban tolerance, and no evidence of an effect of urban environments on the wet range edge. Urban environments appear to broadly buffer range-limiting challenges for urban-tolerant species, which increases our understanding of how anthropogenic environments influence species’ distributions.Item The Impact of Insulin signalling on a C. elegans Alzheimer’s Disease Model(2024-11-20) Zhu, Rain Yuhao; Biology; Chin-Sang, IanAlzheimer's Disease (AD) represents a significant challenge in aging societies. Researchers found a strong correlation with diabetic patients more likely to develop AD. This study explores the interaction between AD and insulin signalling by employing a transgenic Caenorhabditis elegans model overexpressing human amyloid beta (Aβ) peptides, a hallmark of AD pathology. My findings reveal that C. elegans overexpressing Aβ exhibit phenotypes, including impaired neuronal morphology, decreased mobility, and reduced chemotactic responsiveness compared to wild-type counterparts. Remarkably, decreasing the insulin and insulin-like signalling (IIS) pathway via an insulin receptor daf-2(lf) mutation or expression of antagonistic insulins not only suppressed these adult phenotypes but also alleviated similar impairments observed in the earliest larval stage (L1), such as reduced starvation survival and motility. These results challenge the prevailing notion that AD's impact is predominantly a consequence of aging and instead suggest that early-life interventions in the IIS pathway could offer a strategic countermeasure against t Alzheimer’s Disease progression. My study highlights the potential of the IIS pathway as a therapeutic strategy against AD, opening avenues for research into regulating IIS at various life stages.Item Travel through time and space: Temporal and geographical patterns of resistance gene copy number variation, and variation in flowering phenology in glyphosate resistant Amaranthus palmeriNgo, Charlotte; Biology; Yakimowski, SarahHerbicide-resistant weeds offer key insights into rapid adaptation under anthropogenic stress. Amaranthus palmeri, a major agricultural weed native to the southwestern U.S. and Mexico, has developed glyphosate resistance primarily through 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number variation (CNV), with up to 160 copies in contemporary populations. A critical question is whether this CNV predates glyphosate’s commercialization in 1974, potentially indicating standing genetic variation's role in resistance evolution. I analyzed herbarium samples from three time periods (pre-1974: n = 383, 1974-1995: n = 286, post-1995: n = 246). No CNV was detected prior to 1974, with all individuals carrying a single EPSPS copy. After 1974 but before GM crops, occasional CNV was observed (max of 8 copies), but no significant relationship with year. Post-1995, CNV increased significantly, reaching up to 110 copies, suggesting resistance evolved primarily through de novo mutations under glyphosate selection. I also examined geographical patterns and the impact of EPSPS CNV on flowering phenology through a greenhouse experiment involving 19 populations from Georgia, North Carolina, and Illinois. Despite wide CNV variation, no significant relationship was found between CNV and flowering time, indicating resistance does not drive key phenological shifts. However, latitude significantly influenced flowering phenology and inflorescence length, though not plant growth. With the expansion of A. palmeri across North America and currently into Canada, it is imperative we understand historical and contemporary factors that contribute to evolution of herbicide resistance. The historical samples are useful resources to elucidate temporal variation of herbicide resistance, and the contemporary samples are used to understand the relationship between herbicide resistance and geography on flowering phenology.Item Spatial Ecology of Smallmouth Bass (Micropterus dolomieu) in the St. Lawrence River(2024-10-29) Row, Alexander; Biology; Tufts, BruceSmallmouth Bass (Micropterus dolomieu) are an important sportfish in the connected waters of Lake Ontario and the St. Lawrence River and provide large socio-economic benefits. For several reasons, including increasing pressure from competitive angling events, as well as uncertainty about the state of the Smallmouth Bass population arising from provincial and state assessment programs, there is an urgent need for more information about the spatial ecology of this species in these waters. The St. Lawrence River provides a unique opportunity to examine the spatial ecology of this species in habitats without a thermocline. This study used acoustic telemetry with pressure (dBar ≈ depth in m) and temperature sensors to examine the spatial ecology of Smallmouth Bass in the Forty Acre Shoal, which is a section of the St. Lawrence River that contains deep water areas (>20 meters) as well as an abundance of connected shallow (<20 meters) habitat. Smallmouth Bass occupied similar depths as found in previous studies, indicating that factors other than temperature might play an important role in summer depth selection. Home range estimates (95% and 50% Minimum Convex Polygons) were more than double the size of estimates from a nearby study in Lake Ontario. The home ranges of individuals in this study indicate that Smallmouth Bass caught during competitive fishing events are likely displaced well beyond their established home ranges where return rates and long-term effects are currently unknown. Preferred depths and activity rates varied seasonally, with winter characterized by deeper depths and reduced horizontal activity relative to summer. Large movements during winter were also found, providing further evidence that reduced movement and activity during winter may be facultative instead of obligate. This thesis improves our understanding of the spatial ecology of Smallmouth Bass within the St. Lawrence River and provides important considerations for assessing, managing, and conserving the Smallmouth Bass populations in large waterbodies.