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

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Fungal Pathogens of Wasabi in British Columbia

Date created: 
2017-11-06
Abstract: 

Wasabi (Wasabia japonica L.) is a high-value crop in British Columbia and is cultivated in greenhouses where diseases cause economic losses and insect pest issues are emerging. A review of the current literature on wasabi reveals a lack of information on wasabi pest and disease management, especially in North America. The objective of this research was to identify current diseases affecting wasabi in BC isolates from plants showing symptoms of leaf blight, leaf spot, and white blister rust were identified by molecular and morphological methods. Results revealed that Botrytis cinerea, Collectotrichum higginsianum, and Albugo candida were present. Inoculation studies showed B. cinerea was weakly pathogenic, while C. higginsianum caused lesions on wasabi and Brassica juncea, but not on alfalfa (Medicago sativa). In culture, fastest growth of C. higginsianum occurred at 25 and 30°C, and the highest conidial production occurred under continuous darkness. Isolates of A. candida from shepherd’s purse (Capsella bursa-pastoris) plants were identical to those from wasabi, suggesting a source of inoculum. Disease control in an integrated pest management system will remain an important aspect of mitigating economic losses.

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

Assessing the ecological and socioeconomic impacts of the lionfish invasion in the Wider Caribbean Region

Author: 
Date created: 
2017-09-11
Abstract: 

Environmental changes of different scales and magnitudes are occurring at an alarming pace throughout the globe. As natural and human systems resist, cope, and/or adapt to global changes, new equilibrium states might be reached. To understand these changes we need to obtain information relevant to both biological and human systems and the interactions within and between them. My thesis combines approaches from ecology and socioeconomic to investigate the impacts of a specific stressor - invasive Indo-Pacific lionfish - on coral reef ecosystems. First, I explore how this invasion has changed trophic interactions and food web dynamics of coral reef fish communities. Second, I investigate how the impacts of an invasive predator can scale up to affect and change socioeconomic systems associated with natural systems. I found that the trophic niche of lionfish has changed over time, concomitant with large changes in native fish prey abundance. I also found that lionfish predation is having impacts on energy flow through coral reef fish communities even in the absence of marked changes in fish community structure. Combined, these changes could affect ecosystem function. I also present some of the first evidence of economic impacts of this invasion in regions that depend on reef-related tourism. I show that reductions in lionfish abundance through management actions should be beneficial to the reef tourism industry, and that tourist user fees are an acceptable means of financing such actions. As new management strategies are explored, the popularity of lionfish tournaments (derbies) has increased, premised on the idea that involving the public could help to tackle this invasion. However, my results show that such events are most likely to be successful only when lionfish densities are high and where there is a large pool of participants. This dissertation sheds light on the need to study and manage the impacts of biotic invasions from a multidisciplinary and integrated perspective since impacts will rarely be limited to the natural system affected by invaders.

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

Breeding productivity, phenology and habitat use of two co-occurring aerial insectivores

Author: 
Date created: 
2017-09-29
Abstract: 

Aerial insectivores have been declining across North America for several decades, but the main causes of, and reasons for geographical variation in, these declines remains unclear. I directly compared variation in breeding phenology and productivity in co-occurring populations of Barn Swallows (Hirundo rustica) and Tree Swallows (Tachycineta bicolor), and the post-fledging survival and habitat use of Barn Swallows, in the lower mainland, BC, Canada. Barn Swallows had smaller clutches, and later average lay dates, but both species responded similarly to warmer spring temperatures, and interspecies differences were largely independent of habitat. Barn Swallows also had low post-fledgling survival rates, which could negatively impact population dynamics of the species in this region. Overall, our results indicate there are minor interspecies differences on the breeding grounds and therefore variation in species population trajectories in the lower mainland likely occur during the post-fledging stage, migration or on the wintering grounds.

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

Identification and characterization of bacterial and host epithelial factors altered during Edwardsiella infections

Author: 
Date created: 
2017-09-29
Abstract: 

Bacteria in the genus Edwardsiella cause hemorrhagic septicemia in fish hosts, and severe diarrhea in immunocompromised humans. These phenotypes generally require effector proteins secreted through type III and type VI secretion systems. In this thesis, I investigate 2 common bacterial targets, cytoskeleton and intercellular junctions, in epithelial cells to understand the sub-cellular alterations caused by Edwardsiella during these infections. Using two robust epithelial infection models (HeLa and Caco-2 cells) I show that host microtubules are destroyed during the progression of Edwardsiella infections, while the actin and intermediate filaments remain unaltered. My evidence points to the host microtubule severing enzymes as key players in the microtubule disassembly event as katanin A1 and the katanin A1 subunit-like 1 proteins both localize to the microtubule cut-sites. The novelty of this phenotype extends to the bacteria, as this phenotype is independent of both type III and type VI secretion systems. Negative screening using an E. piscicida transposon insertion mutant library identified 15 bacterial genes needed for host microtubule severing event. The thesis concludes with preliminary examination of host intercellular junction alterations where I demonstrate that the tight junction protein claudin-3 is dissociated from cell peripheries in infected cells. In conclusion, I uncovered two steps of Edwardsiella’s infectious process where host structural components are targeted—leading to phenotypes observed during edwardsiellosis.

Document type: 
Thesis
File(s): 
S1 video - Microtubule disassembly in HeLa cells
Senior supervisor: 
Julian Andrew Guttman
Ka Yin Leung
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

Direct and indirect interactions between owls, mice and nocturnal seabirds: integrating marine and terrestrial food webs

Author: 
Date created: 
2017-07-31
Abstract: 

Climate variability in semi-arid ecosystems can influence species interactions from the bottom-up, and through these perturbations we can gain insight into both direct and indirect interactions in food webs. In this thesis, I studied the effects of ENSO-driven rainfall pulses and drought on the interactions between a top predator, the Barn Owl (Tyto alba), a mesopredator, an island endemic deer mouse (Peromyscus maniculatus elusus), and a threatened nocturnal seabird, the Scripps’s Murrelet (Synthliboramphus scrippsi). On Santa Barbara Island in the Channel Islands National Park in California, adult breeding murrelets are killed by owls, but their eggs are eaten by mice, which is the main cause of reduced murrelet nest success. First, I assessed how owl predation on murrelets varies with the availability of mice, the primary prey of owls. I found that heavy rainfall years drive the irruptions in the mouse population that precede peaks in owl abundance, which results in high murrelet predation by owls when the mouse population subsequently crashes. Next, I examined evidence for positive indirect effects of owls on murrelets through their influence on mouse foraging behavior. I found that mouse foraging was strongly suppressed as the abundance of owls increased, and survival of murrelet eggs was also positively related to owl abundance. I also examined how both the terrestrial and marine environments influenced overall murrelet nest success over a span of 21 years. I found that the severity of drought was the most important variable determining nest success, which suggests that during severe droughts, mice consume substantially more eggs when there are fewer terrestrial resources and also less risk from predation. Climate-driven indirect interactions with predators therefore influences both survival and nest success of murrelets on this island. Finally, I developed a mathematical model of island community dynamics to assess whether owl management might benefit murrelets given projected changes to rainfall patterns in this region. I found no evidence that managing the owl population would enhance murrelet abundance, demonstrating the importance of considering both direct and indirect effects of predators when evaluating potential conservation strategies.

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

The magnetic sense of honey bees - analyses of underlying mechanisms and potential function

Author: 
Date created: 
2017-11-10
Abstract: 

I studied a potential function and underlying mechanism(s) of the magnetic sense in honey bees, Apis mellifera. A waggle-dancing bee informs hive mates about a food source. Directional information pointing to the food source relative to the sun's azimuth is encoded in the angle between the straight segment of her waggle dance and a reference line such as gravity or the local geomagnetic field (LGMF). Neither cancelling the LGMF nor shifting its declination affected the recruitment success of waggle-dancing bees, implicating gravity as the reference line for the dance alignment. To study the underlying mechanism(s) of the bees’ magnetic sense, I analyzed lyophilized and pelletized bee tagmata by a Superconducting Quantum Interference Device. A distinct hysteresis loop for the abdomen but not for the thorax or the head of bees indicated the presence of magnetite in the abdomen. Magnetic remanence of abdomen pellets produced from bees that I did, or did not, expose to an NdFeB magnet while alive differed, indicating that magnet-exposure altered the magnetization of this magnetite in live bees. Following exposure of live bees to the same magnet, magnetized bees, unlike sham-treated control bees, failed to sense the presence of a magnetic anomaly, demonstrating a functional connection between magnetite in the abdomen and the magnetoreceptor, and temporary or permanent disablement of the receptor through magnet-exposure. To test whether bees sense the polarity of a magnetic field, I trained bees to associate a magnetic anomaly with a sugar water reward. I then presented trained bees with a sugar water reward in two separate watch glasses, placing one reward in the center of the anomaly that I either kept the same as during bee training (control experiment) or that I altered by reversing its polarity (treatment experiment). That bees continued to recognize the magnetic anomaly when its polarity was kept unaltered, but failed to recognize it when its polarity was reversed, indicates that bees have a polarity-sensitive magnetoreceptor. To increase the detectability of magnetite in bee tissues, I lyophilized samples to reduce water content, maximized the signal amplitude by pelletizing samples, and accounted for sample dimensions in data analyses.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Gerhard Gries
Michael Hayden
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.

Habitat drivers of Barn Swallow (Hirundo rustica) feeding behaviour and breeding productivity

Date created: 
2017-08-11
Abstract: 

Barn Swallows Hirundo rustica belong to a declining guild of birds, and much remains unknown about the causes of these declines. Research in Europe has shown that pastures, hay fields, and livestock benefit Barn Swallow populations, and this study aimed to determine whether similar trends are found in a North American context. We studied this in two ways, first, by examining breeding productivity in three different habitats and then by examining how much they fed over certain types of fields. Breeding productivity parameters of swallows were largely similar although there were some differences, with higher fledging success in crop habitat and a higher proportion of intermediate nests in non-agricultural habitat in one of the years, however the overall picture suggests that non-agricultural, crop, and livestock are largely similar to one another, unlike what was found in European studies. Weather and manure management may have a greater impact on breeding productivity and warrant future research. We also found no difference in Barn Swallow feeding over grassland set-aside and cultivated fields, though the insect communities were different.

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

The role of pathogen diversity on the evolution of resistance

Author: 
Date created: 
2017-09-21
Abstract: 

My aim is to determine whether baculovirus diversity affects the rate at which resistance evolves. Using Trichoplusia ni as a host, changes in resistance against single versus mixtures of AcMNPV variants were examined in an evolution experiment. AcMNPV variants were isolated using dilution cloning and characterized using RFLP and pathogenicity bioassay. I found that the rate of evolution of resistance to more diverse pathogen infections to be less than that of single variants and the level of resistance was reduced by over 284-fold compared to specific single variants. Identity of the single variants had a major influence on the rate of evolution of resistance. Additionally, I found evidence of higher fitness costs of resistance to more diverse infections. My findings indicate that pathogen diversity should be factored into resistance management strategies for microbial insecticides and provide insight into the role of pathogen diversity on the evolution of resistance to pathogens.

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

New Food Baits for Trapping German Cockroaches Blattella germanica (L.)

Date created: 
2017-06-27
Abstract: 

New trap baits were designed and tested for attracting German cockroaches (GCRs), Blattella germanica. In large-arena laboratory experiments, traps baited with rye bread captured 8-fold more GCR males than unbaited control traps. Neither beer nor water enhanced the attractiveness of bread. As Porapak Q headspace volatile extracts of rye bread attracted GCRs, all odorants in extracts were identified by gas chromatography-mass spectrometry. A blend of synthetic rye bread odorants and other known bread odorants was highly attractive to GCRs but the essential components in that blend are yet to be determined. In and field trapping experiments, both a 3-component composition (3CC) [dry malt extract (DME), water, Brewer’s yeast] and DME alone were as effective for attracting GCRs as a commercial cockroach bait. Future studies will investigate lethal biocontrol agents that can be added to the 3CC, or the DME, and will explore the efficacy of such baits for GCR control.

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

Exploring the efficiency of Evolutionary Distinctness in conservation prioritization

Author: 
Date created: 
2017-04-19
Abstract: 

In this Age of Extinction, we must prioritize the species we want to conserve. Conservation programs use different metrics for species prioritization, but more work is needed linking these metrics to particular aspects of biodiversity value. Here, I focus on the species-specific conservation metric of Evolutionary Distinctness (ED) designed to identify species with few close relatives. I first explore the relationship between ED and a presumed valuable attribute, the average rarity of traits. Using simulations, I find high degrees of association between ED and trait rarity; however unlike another metric of isolation (Average Pairwise Distance) this ability decreases as higher gamma clades are sampled. I then examine, under different scenarios of extinction, how well ED captures a related touted value, total phylogenetic diversity (PD). I find a very strong correlation between PD and ED across all surveyed trees. Overall, ED is not perfect, but shows some promise as a simple conservation metric, capturing at least two related measures of biodiversity value.

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