Biological Sciences - Theses, Dissertations, and other Required Graduate Degree Essays

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Microplastics in the Beaufort Sea Beluga Food Web

Author: 
Date created: 
2020-02-06
Abstract: 

Microplastics (MPs, particles <5 mm) represent an emerging global environmental concern and has been detected in multiple aquatic species. Very little is known, however, about the presence of MPs in higher trophic level species, including cetaceans. Working in collaboration with Inuvialuit hunters from Tuktoyaktuk (Northwest Territories, Canada) and researchers from the Department of Fisheries and Oceans, entire stomachs and intestinal sub-sections were collected from seven beluga whales (Delphinapterus leucas) in 2017 (n=4) and 2018 (n=3) for examination. Microplastics were detected in the gastrointestinal tracts in every whale. Each whale contained an estimated 18 to 147 MPs in their GI tract with an average of 97 ± 42 per individual. FTIR-spectroscopy revealed over eight plastic polymer types, with nearly half being polyester. Dominant MP types were equally present, with fragments making up 51% and fibres 49%. The potential source of MPs to beluga via prey items was also determined by examining the GI tracts from five Arctic fish species belonging to the beluga food web (n=116). Species investigated included (Arctic cod (Boreogadus saida), saffron cod (Eleginus gracilis), Arctic cisco (Coregonus autumnalis) four-horn sculpin (Myoxocephalus quadricornis) and capelin (Mallotus villosus). Microplastics were found in 21% of prey. The fish that contained microplastics had a mean abundance of 1.42 ± 0.44 particles per individual and 85% of particles observed were fibres. Particle size and polymer types found in prey were similar to those found in beluga, suggesting that trophic transfer of MPs from prey to beluga may be occurring. The diversity of MP shapes and polymeric identities in all species investigated points to a complex source scenario, and ultimately raises questions regarding the significance and long-term exposure of this pollutant in these ecologically and culturally valuable species.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Leah Bendell
Peter Ross
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

Reproductive and thyroid endocrine axis cross-talk in rainbow trout (Oncorhynchus mykiss) alevins

Author: 
Date created: 
2020-04-27
Abstract: 

Although numerous studies on various aspects of endocrine axes and the physiology of both juvenile and adult life stages of several teleosts exists, studies characterizing the basic functions and cross-talk of endocrine axes during early developmental stages (i.e. embryonic to early feeding fry), in particular, are limited. The goal of this study was to characterize morphological and molecular effects in rainbow trout alevins after waterborne exposures to 17β-estradiol (E2 0.0008 to 0.5 μg/L), triiodothyronine (T3; 0.52 to 65 μg/L), and various co-treatments for 21 to 23 days. Interestingly, there was no consistent evidence that E2 alone influenced growth, development or deformity rates, nor the co-treatments of 0.02 and 0.1 μg/L of E2 with up to 65 μg/L of T3. However, 13 and 65 μg/L T3 alone expedited development and caused a unique opercular deformity not previously reported. Gene expression changes were observed, but these were mainly at the highest concentrations tested. These data suggest low-level E2 does not negate abnormal growth and development caused by hyperthyroidism and examining more time points is likely required to demonstrate a stronger response profile for individual hormones and endocrine axes cross-talk.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Vicki Marlatt
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

Fish community dynamics and nursery habitats in an undeveloped estuary

Author: 
Date created: 
2020-01-31
Abstract: 

Estuaries are potentially critically-important fish habitats. However, their temporal and spatial dynamics challenge understanding of the nursery functions of estuaries. Working in the Koeye River estuary in British Columbia, I used size-spectra analysis to infer production and predation risk across the estuary habitat mosaic and track their changes through the season. The brackish mudflat habitat exhibited the highest fish production and lowest inferred predation risk, suggesting that this area had particularly high nursery value. Spectra coefficients were seasonally dynamic, indicating that temporal shifts in the spatial patterns of risks and reward. I also investigated the potential effects of climate change on the distributions of different estuarine fish assemblages by comparing two climatically-divergent sampling seasons. Marine-oriented species expanded their range up-estuary during the dry, more saline year, but freshwater species did not shift. Collectively, this research advances understanding of the spatio-temporal dynamics of estuary nursery functions.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Jonathan Moore
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

Habitat use and the impacts of agricultural land use for wintering Neotropical migrants

Author: 
Date created: 
2020-01-10
Abstract: 

For six months of each year, Neotropical forests host the highest known diversity and density of wintering migrants. Habitat loss and conversion of more than 3.5 million ha of Neotropical forests a year is frequently linked to declines in Neotropical migrants, however, data on habitat use in the wintering grounds is very limited. In this thesis, I examine habitat use, across three land cover types for wintering Yellow Warblers (Setophaga petechia) and show that in the lowlands of Jalisco, Mexico, seasonal agriculture with hedgerows, provides high quality winter sites. Yellow Warbler originating from Western Canada, were found in the highest densities in agricultural habitats, intermediate in riparian forests and lowest in coastal scrub-mangrove. Birds wintering in agriculture and riparian forest had higher apparent monthly survival compared to birds in scrub-mangrove and were able to regrow higher quality replacement tail feathers. However, I found no evidence that traits linked to competitive ability (age, sex, or size) influenced the distribution of birds across different land covers. Together, these results demonstrate that current agricultural practices in western Mexico are unlikely to have contributed to the decline of Yellow Warbler populations in Canada. Overwintering in agriculture did not appear to negatively impact the Neotropical migrant community in western Mexico. Neotropical migrants were more abundant in agriculture, and had similar species diversity and beta-diversity to riparian forests. In contrast, although a few resident species were frequently found in agriculture, resident species had lower species diversity in agriculture compared to riparian forest community. Collectively these results demonstrate that individual species, and particularly the Neotropical bird community can utilize human altered landscapes on the wintering grounds in Mexico. However, native habitats are key to retaining the full resident bird community. Identifying the features and spatial configuration of the working land that supports bird populations will be critical for the management and conservation of resident and overwintering birds.

Document type: 
Thesis
File(s): 
Senior supervisor: 
David Green
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.

Efficacy of the European Earwig (Forficula auricularia) as a generalist biocontrol agent

Author: 
Date created: 
2025-12-13
Abstract: 

The European Earwig (Forficula auricularia) has been the subject of scientific curiosity and public disdain since its introduction to North America due to its controversial status as both a natural enemy of agricultural pests, and as a nuisance cohabitant of human dwellings. I aim to investigate the feasibility of utilizing the earwig as a biocontrol agent against target pests of organic apple orchards, as well as its efficacy as a generalist predator in the context of agricultural ecosystems. Through DNA gut-content analysis, and cross-seasonal field observations, I was able to confirm that earwigs are consuming apple orchard pests under natural conditions. These findings are corroborated upon further analysis of field data which show a negative association between earwig abundance and multiple species of pest prevalence at tree-level occupancy across the field season. I examine predation efficacy and consumptive thresholds of the earwig in the context of generalist predator traits through temperature controlled functional response laboratory experiments for two recognized apple pest species, the rosy apple aphid (Dysaphis plantaginea), and the oblique-banded leafroller (Choristoneura rosaceana). Earwig predation was independently affected by density and temperature, but no interaction effect was observed. Analysis of the data did not accurately describe a type II functional response relationship, showing the limitations of traditional predator-models for describing predation behaviour of generalists in biocontrol practice. The preponderance of evidence outlined in this thesis provides promising evidence for utilizing European earwigs in conservation biocontrol, elucidates their role as key predators in agroecosystems, as well as reconsiders how to approach the study of generalist predators in biocontrol research and traditional predator-prey models.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Jenny Cory
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.P.M.

Reproductive trade-offs in the click beetle, Agriotes obscurus, exposed to the fungal pathogen Metarhizium brunneum

Author: 
Date created: 
2019-09-20
Abstract: 

Several of the more pathogenic fungal species that infect insects have been developed as biological control agents. Adult insects can respond to potentially lifespan-reducing pathogen challenges by fighting infection, allocating resources to resistance over other activities. Alternatively, they can allocate resources to maximizing fecundity in response to early death, the terminal investment hypothesis. The click beetle Agriotes obscurus is an agricultural pest, and the fungus Metarhizium brunneum is being developed as a control agent. I examined the impact of M. brunneum challenge on A. obscurus reproduction and whether this changed under different nutritional conditions in beetles of varying ages. Beetles reduced their preoviposition period in response to fungal-induced decreases in lifespan when they were older, resulting in maintained fecundity, or under starved conditions, although fecundity could not reach the level of fed beetles. These results suggest that M. brunneum should be used early in the season when resources are abundant.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Jenny Cory
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.P.M.

Conceptual and applied approaches to marine invasions

Author: 
Date created: 
2019-09-24
Abstract: 

The accelerating rise in global trade and travel means that our world is more interconnected than ever before. This trend could severely impact species and ecosystems globally, as it increases opportunities for species to invade regions beyond their natural range. In this thesis, I combine ecological theory and data synthesis with empirical field-studies to tackle the questions of what makes some communities more easily invaded than others, and how can both natural and anthropogenic control interventions affect the persistence and impacts of invasive species. I first evaluate the relationship between native species diversity and invasibility, or the vulnerability of a community to invasion. Using a meta-analytic approach, I show that the conflicting patterns between diversity and invasibility that are often observed in the literature are likely due to not only differences in spatial scales between studies but also to differences in the metrics researchers use to measure invader success. I then use the invasion of Caribbean coral reefs by the predatory Indo-Pacific lionfish as a model system to test natural and anthropogenic means of controlling the invader. Using a combination of fisheries-derived sampling of native grouper predators and a field experiment conducted across a gradient of grouper abundance, I examine the ability of native grouper predators to mitigate the negative effects of lionfish predation in the Bahamas. I reveal little evidence for direct predation by groupers on lionfish, but show that fear of native groupers alone by lionfish is sufficient to evoke behavioural changes in lionfish that could potentially reduce their impact on native prey. Finally, I use a long-term field experiment to investigate the ecological effectiveness of infrequent culling (i.e., the physical removal of lionfish from reefs by divers). I demonstrate that infrequent culling can reduce lionfish abundance, but is insufficient to halt the decline in native prey fish biomass. Moreover, I show that large-scale natural disturbances, like hurricanes, and density-dependent movement by lionfish from neighbouring reefs can undermine culling efforts. Overall, my thesis reveals that the development of standardized metrics is key to generate a holistic understanding of invasion dynamics, and that both natural and anthropogenic control over invaders is unlikely to stymy biological invasions at the scale currently observed for Indo-Pacific lionfish in the Caribbean.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Isabelle M. Côté
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.

Repurposing historical data to investigate aerial insectivore declines

Date created: 
2019-09-09
Abstract: 

Populations of aerial insectivores have decreased since the mid-1980s, possibly due to declines in their prey. However, long-term data on insect abundance in North America are lacking. I evaluated whether brood size manipulation experiments could be repurposed to assess changes in insect availability. A literature review found no evidence that parents’ ability to respond to a challenge has changed over time, but study methods varied widely. Therefore, I replicated a brood size manipulation experiment conducted on tree swallows in 1994/1995. Parents did not change how they responded to changes in brood size. However, delivery rates were consistently lower in 2017/2018 because parents delivered smaller boluses and tended to visit the nest less. These results are consistent with the hypothesis that aerial insectivores are declining due to reduced insect availability, but could also arise for other reasons. My thesis highlights the value of historical data for investigating aerial insectivore population declines.

Document type: 
Thesis
File(s): 
Senior supervisor: 
David J. Green
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

The evolutionary origins of amphibian extinction risk

Author: 
Date created: 
2019-09-18
Abstract: 

The rise of humanity to ecological dominance has precipitated concerted patterns of environmental change across every biome on Earth. Human activities can upend the adaptive landscapes on which species' have evolved, causing the sudden maladaptation of lineages to these novel conditions. Amphibians are amongst the most threatened vertebrates, with contemporary extinctions driven by multiple interacting stressors including habitat destruction, introduced pathogens, and climate change. Despite these looming threats, we understand little about how or why susceptibility to these stressors varies across amphibian lineages. In this thesis, I investigate the evolutionary origins of modern extinction risk in the Amphibia, by examining comparative patterns of susceptibility to various drivers of extinction. First, I show that modern extinction risk positively covaries with speciation rates across amphibian genera due to the most rapidly-diversifying clades producing numerous range-restricted and vulnerable species. Second, I demonstrate how evolutionary dynamics may influence local-scale extinction by examining amphibian species' responses to deforestation across the world. Contrary to patterns of global threat, the slowest-diversifying amphibian lineages are disproportionately lost from human-modified ecosystems - which may reflect a relationship between diversification and niche lability. Third, I examine phylogenetic and trait-based patterns of susceptibility to a human-dispersed fungal pathogen. Though species' ecology and life history consistently shape infection patterns across diverse amphibian assemblages, these traits appear to bear little weight for species' extinction risk from disease epidemics. Fourth, I test the relative effects of both dehydration and temperature on performance, and therefore climate risk, in three ecologically diverse anuran species. Performance was maintained across broad thresholds of dehydration in all species, but warmer temperatures accelerated the onset of performance decline. Species-specific biophysical modelling revealed stark differences in how dehydration is likely to limit activity in each species, suggesting that desiccation physiology may be an important driver of extinction risk from climate change in amphibians. These studies collectively illustrate that amphibian species' responses to anthropogenic environmental change have deep evolutionary roots. In turn, we can expect our continued environmental dominance to fundamentally reshape the evolutionary tree of amphibians into the future.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Wendy Palen
Arne Mooers
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.