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

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Life History and Chemical Ecology of Xenos peckii (Strepsitera, Xenidae)

Author: 
Date created: 
2015-07-27
Abstract: 

I investigated life history traits and pheromonal communication of Xenos peckii, a parasitoid of the paper wasp Polistes fuscatus. To emerge, males cut the puparium with their mandibles, and then push aside the pupal cap with their head. The endoparasitic females engage in active calling (pheromone release) behaviour assuming a particular body posture. Seasonal and diel emergence periods of males coincide with seasonal and diel calling periods of females. Mate-seeking males land on the anterior portion of the host wasp’s abdomen, and then step backward until their mesothoracic legs contact the female’s cephalothorax, upon which the male initiates copulation. Analyzing pheromone gland extracts by gas chromatographic-electroantennographic detection revealed a candidate pheromone component (CPC) that consistently elicited responses from male antennae. CPC was identified as (7E,11E)-3,5,9,11-tetramethyltridecadienal based on mass and NMR spectra, and the synthesis of an authentic standard. In field experiments, traps baited with synthetic CPC captured X. peckii males.

Document type: 
Thesis
File(s): 
Female Xenos peckii assuming her mate-calling posture (16x speed).
Emerging male using his mandibles to cut along the ecdysial suture line.
Male Xenos peckii emerging from his puparium.
Mating sequence of Xenos peckii (filmed at 1000 fps).
Mating sequence of Xenos peckii (30 fps, real-time).
Senior supervisor: 
Gerhard Gries
Carl Lowenberger
Department: 
Science: Biological Sciences
Thesis type: 
(Thesis) M.Sc.

The effects of six organophosphate flame retardants on endocrine receptor targets in mammalian cancer cell lines

Date created: 
2015-05-20
Abstract: 

The effects of six selected organophosphate flame retardants (OPFRs) tris(2-butoxyethyl) phosphate (TBOEP), tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), tris(methylphenyl) phosphate (TMPP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and triethyl phosphate (TEP) on the activities of the androgen-, estrogen- and aryl hydrocarbon receptors were assessed in human prostate cancer cells (LNCaP) and endometrial cancer cells (ECC-1 cells). Binding affinity for the estrogen receptor (ER) of the selected OPFRs appeared limited in ECC-1 cells, as no profound changes in ER inducible target gene expression were observed. Furthermore, the six selected OPFRs exerted few effects on the aryl hydrocarbon receptor-inducible CYP1A1 expression, although at high concentrations TMPP mildly induced gene expression. Messenger RNA and protein accumulation of androgen receptor (AR) target genes were examined for TDCIPP. Additionally, secretory PSA detection, chromatin immunoprecipitation and a ligand binding assay were performed using TDCIPP and the synthetic androgen methyltrienolone. AR inducible target gene and protein expression were significantly altered by TDCIPP exposure, as well as excreted prostate specific antigen. For the first time it was demonstrated that TDCIPP does not have binding affinity for the AR-ligand binding domain and appears to exert its anti-androgenic effects in LNCaP cells in a non-competitive fashion. Furthermore, TDCIPP exposure could adversely influence clinical outcomes for prostate cancer screenings, resulting in false negatives. Prolonged TDCIPP exposure could also carry the risk of exacerbating the progression of prostate cancer into a metastatic androgen-independent sub-type by simulating androgen deprivation.

Document type: 
Graduating extended essay / Research project
File(s): 
Senior supervisor: 
Dr. Timothy Beischlag
Department: 
Science: Biological Sciences
Thesis type: 
(Project) M.E.T.

The pappalysins and their substrates in early pregnancy

Author: 
Date created: 
2014-05-14
Abstract: 

Abnormal levels of pregnancy-associated plasma proteins -A and -A2 (PAPP-A and PAPP-A2) have been associated with adverse pregnancy outcomes, including preeclampsia and intrauterine-growth-restriction, two leading causes of maternal and perinatal mortality. The goal of this thesis was to assess the roles of PAPP-A, PAPP-A2, and their substrates, insulin-like growth factor-binding proteins -4 and -5 (IGFBP-4 and IGFBP-5), in early pregnancy. In contrast to previous findings with PAPP-A, first trimester maternal serum levels of PAPP-A2 were elevated in pregnancies that subsequently developed preeclampsia. In a model of early placental development, IGFBP-4 and IGFBP-5 inhibited the migration-stimulating effects of insulin-like growth factors -I and -II, although to different extents. Investigation of the location of IGFBP-4 and IGFBP-5 in the placenta revealed sites of protein localization that suggest previously unknown functions. Taken together, these findings suggest different roles of PAPP-A and PAPP-A2 in the first trimester placenta.

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

The identification and characterization of bacterial and host epithelial factors involved in the pathogenesis of invasive Francisella tularensis and extracellular enteropathogenic E. coli (EPEC)

Author: 
Date created: 
2015-04-22
Abstract: 

Enteropathogenic Escherichia coli (EPEC) and Francisella tularensis possess a toolkit of virulence factors that allow them to adapt to the host environment and prevail over the body’s natural defenses in different ways. For diarrheagenic EPEC, a type III secretion system is used to inject virulence factors directly into the host cell allowing the extracellular microbe to co-opt key host processes and generate motile ‘pedestal’-shaped structures at the site of intimate bacterial-host contact. Because many of the same principles that drive the biogenesis and movement of EPEC pedestals are paralleled at the leading edge of migrating cells, I used EPEC pedestals as a model of the leading edge and developed a strategy to identify pedestal proteins and tease out their biological functions. Using mass spectrometry-based proteomics of concentrated pedestal preparations, I identified 17 highly abundant novel proteins as well as 11 previously known pedestal proteins. One of the identified molecules, nexilin, was characterized in depth. Using EPEC and Listeria monocytogenes as bacterial models for actin-based dynamics, I revealed that nexilin is concentrated towards the rear of pedestals and Listeria comet tails when these actin-rich structures become motile. The use of siRNA-mediated knockdowns further suggested that depletion of nexilin results in unusually thin and short filamentous comet tails. Another pathogen that can colonize non-phagocytic cells is F. tularensis—the etiological agent of Tularemia. Here, I examined the internalization process and intracellular fate of Francisella in hepatocytes. To study the strategy that F. tularensis uses to invade epithelial cells I developed in vitro infection models and used those models to uncover clathrin, its associated endocytic components and cholesterol as key molecules needed for F. tularensis internalization. Finally, I elucidated the role of two Francisella virulence factors (IglC, PdpA) and showed that both PdpA and IglC are needed for the efficient invasion and intracellular growth of F. tularensis. Taken together, I have identified multiple novel targets co-opted by the extracellular EPEC and the intracellular pathogens L. monocytogenes and F. tularensis that play a central role in their pathogenesis such as the actin associated protein nexilin and clathrin endocytic components clathrin, epsin1, and Eps15.

Document type: 
Thesis
Senior supervisor: 
Julian Guttman
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Assessment of embryotoxicity, post-hatch development, and long-term effects on behavior and reproduction in zebra finches (Taeniopygia guttata) following in ovo methylmercury exposure

Author: 
Date created: 
2015-04-16
Abstract: 

Mercury is an environmental contaminant that can bioaccumulate in terrestrial ecosystems as organic methylmercury (MeHg); however little is known on the effects of mercury exposure on terrestrial-feeding songbirds. The objectives of the current study were to 1) assess embryotoxic effects of in ovo exposure, via egg injection, to MeHg concentrations similar to those reported in free-living songbirds; and 2) investigate long term post-hatching effects of in ovo exposure to MeHg on offspring development, mating behavior, and reproduction in a model songbird species, the zebra finch (Taeniopygia guttata). In ovo MeHg decreased hatching success in a dose-dependent manner. However, it had no long-term post hatching effects on growth, hematological traits, male courtship song quality, mating behavior in either sex, or female reproductive performance. These findings would suggest that in ovo exposure to MeHg has acute effects on embryo survival, but no long-term effects on the behavioral endpoints measured or reproductive performance.

Document type: 
Graduating extended essay / Research project
File(s): 
Senior supervisor: 
Tony Williams
Department: 
Science:
Thesis type: 
(Project) M.E.T.

Variance and extreme events in population ecology

Date created: 
2015-03-04
Abstract: 

Assessing, managing, and communicating variance and risk is fundamental to effective ecological decision making. One promising approach is to borrow concepts from financial portfolio management. Ecological populations behave like portfolios in many ways—we can treat the abundance of populations, such as salmon in streams, as financial stock value, and groups of populations, such as salmon within a river catchment, as portfolios. If a group of populations react differently to an environmental event then the probability of sudden decline may be lowered, similar to a diversified financial portfolio. This risk reduction has been referred to as the portfolio effect. In this thesis I consider three applications of portfolio concepts to ecology. I begin by evaluating ways of estimating portfolio effects and applying these metrics to moth, reef fish, and salmon metapopulations from around the world. I show an inherent bias to a commonly used method, develop a new method based on Taylor's power law of mean--variance scaling, and outline recommendations for estimating portfolio effects. Next, I use a portfolio approach to inform conservation priorities for salmon populations under a changing climate. I show that preserving a diversity of thermal tolerances minimizes risk and ensures persistence given long-term environmental change. However, this reduction in variability can come at the expense of long-term persistence if climate change increasingly restricts available habitat, forcing ecological managers to balance society's desire for short-term stability and long-term viability. Finally, I take the concept of black swans (extreme and unexpected events) from the financial literature and ask what the evidence is for these events across hundreds of bird, mammal, insect, and fish abundance time series. I find strong evidence for the infrequent (3–5\%) occurrence of ecological black swans. Black swans are predominantly (87%) downward events and tend to be associated with extreme climate, natural enemies (predators and parasites), or the combined effects of multiple factors, with little relationship to life history. My thesis demonstrates the importance of conserving ecological properties that may contribute to portfolio effects, such as thermal-tolerance diversity and habitat heterogeneity, and developing conservation strategies that are robust to unexpected extreme events.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Nicholas K. Dulvy
Andrew B. Cooper
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Effects of anthropogenic disturbance on sensitive wildlife and habitats

Author: 
Date created: 
2015-01-20
Abstract: 

The cumulative ecological impacts of broad-scale anthropogenic disturbances, such as forestry or energy development, are a challenge to predict and evaluate. Here, I evaluate the potential of future run-of-river (ROR) hydropower development to impact riparian ecosystems in British Columbia, Canada. I found the projected spatial footprint of ROR in the riparian zone to be 40 times smaller than the footprint of existing disturbance from forestry, roads, and powerlines, but concentrated in watersheds that currently have low levels of disturbance. Habitat degradation for small riparian vertebrates from ROR development was cumulative with substantial existing impacts. I also tested whether harvest data in Species Distribution Models can aid in evaluating species responses to logging at different scales and sensitivity levels using a simulation framework. I found that logging becomes a strong predictor of species distributions at landscape scales, or when the spatial heterogeneity of forestry exceeds that of other variables (e.g. climatic or topographical) in the model.

Document type: 
Thesis
Senior supervisor: 
Wendy Palen
Department: 
Science: Biological Sciences
Thesis type: 
(Thesis) M.Sc.

Insect-derived hybrid antimicrobial peptides: antibiotics for the next generation?

Date created: 
2014-04-04
Abstract: 

There has been recent interest in utilizing natural antimicrobial peptides (AMPs) as novel antibiotics. Hybrid antimicrobial peptides (hAMPs) are synthetic molecules containing active motifs from multiple parental AMPs. This thesis presents in vitro activity data of hAMPs designed b y combining binding and killing motifs from different invertebrate and vertebrate AMPs. The goals of hAMP design are to improve antimicrobial efficacy and reduce host cytotoxicity. Activity was further optimized by modifying basic properties of the peptide such as charge, hydrophobicity, peptide length and specific amino acid composition. Overall, hAMPs exhibited higher antimicrobial efficacy than their active motifs alone in vitro. Some hAMPs kill bacteria through membrane permeabilization while others likely attack intracellular targets. Synergistic activity was observed when different hAMPs were combined together separately or when combined in the form of a multivalent hAMP. Our results indicate that hAMPs may be suitable for use as novel antimicrobial agents.

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

Multimodal mechanisms of early mate-detection in the parasitoid wasp Pimpla disparis (Hymenoptera: Ichneumonidae)

Date created: 
2015-04-20
Abstract: 

Males of the hymenopteran parasitoid Pimpla disparis have been observed to aggregate on gypsy moth, Lymantria dispar, host pupae before the emergence of a female. This led me to test the hypothesis that males respond to chemical cues associated with parasitized pupae. Results of laboratory experiments suggest that females mark the host pupae they have parasitized and that males discern between such pupae and those not parasitized. Males continue to recognize parasitized pupae throughout the development of the parasitoid. To investigate potential acoustic and vibratory cues that males may exploit to detect the presence and track the progress of a developing parasitoid (DePa; future mate) inside a host pupa, I analyzed DePa-derived cues by airborne sound and laser Doppler vibrometer recordings. Parameters (e.g., amplitude) of sound and vibratory cues change significantly over time and thus could ‘inform’ a visiting adult male about the stage of DePa’s development. To test the hypothesis that male P. disparis memorize and revisit the location(s) of parasitized host pupae as a strategy to attain mates, we color-coded P. disparis males in a field survey and recorded their behaviour. We learned that they revisit parasitized moth pupae on consecutive days, and arrest on those pupae with a near-emergence parasitoid. These results are supported by laboratory experiments, revealing that males memorize both the macro- and micro-locations of parasitized host pupae. DePa’s quiescence a few days before emergence could be a cue for a visiting male that the emergence of a mate will soon take place but it would not help the male to precisely predict the time of emergence. In contrast, oral fluid produced by emerging adult parasitoids may be indicative of the emergence process. I tested the hypothesis that semiochemicals associated with DePa’s emergence arrest males on a parasitized host pupa. I found that these semiochemicals emanate from oral fluid secreted by parasitoids while chewing their way out of a host. Attraction of males to oral fluid semiochemicals from males and females indicates that mate-seeking males co-opt chemicals involved in the eclosion process as a mate finding cue, taking a 50% chance that the prospective mate is a female.

Document type: 
Thesis
File(s): 
Sound recording of a Pimpla disparis larva 8 days post parasitism of the host pupa
Sound recording of a Pimpla disparis pupa 14 days post parasitism of the host pupa
Sound recording of a Pimpla disparis pupa 18 days post parasitism of the host pupa
Video of spinning 14-day-old Pimpla disparis pupa inside host pupa
Video of adult Pimpla disparis chewing its way out of the host pupal case
Senior supervisor: 
Gerhard Gries
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Baculovirus infection, host immunity and pathogen competition in the cabbage looper, Trichoplusia ni

Date created: 
2015-04-22
Abstract: 

Competition between pathogens within a host could change the short term and evolutionary outcomes of an infection. These interactions include resource-based and immune-mediated competition. We understand little about the insect immune response to virus infection and how this alters the host for future co-infecting pathogens. I characterised several immune parameters of the cabbage looper, Trichoplusia ni, in response to challenge by a baculovirus, TnSNPV, and found that all parameters reduced with increasing virus dose. To measure the effect of competing pathogens on virus success, I exposed T. ni to TnSNPV followed by either the bacterium, Bacillus thuringiensis, or the fungus, Beauvaria bassiana. The fungus reduced the infection success of the baculovirus and the bacterium negatively impacted virus replication. This outcome has consequences for microbial control agents in insect pest management and adds to our fundamental understanding of the effect of mixed infections on pathogen and host populations.

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