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

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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.

Individual variation in foraging effort of breeding birds

Date created: 
2017-05-01
Abstract: 

Parental care (e.g. provisioning nestlings) is widely assumed to be costly, and life-history theory predicts a trade-off between reproduction and future fecundity and/or survival. However, experimental studies manipulating workload during parental care and demonstrating fitness effects are either rare or have mixed results. Here, we took a two-step approach to this problem in European starlings (Sturnus vulgaris): 1) using a 4-year dataset to ask if changes in parental investment in handicapped (wing-clipped) parents, and the fitness consequences of these decisions, vary among years (i.e. with ecological context), and 2) using an automated radio telemetry system to determine if females alter their activity to compensate for an increase in workload. We found marked individual and annual variation in response to the handicapping treatment. In addition, clipped individuals dramatically reduced their activity, while sustaining current breeding productivity, suggesting that clipped individuals reduce self-maintenance to favour their current reproductive bout.

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

Genetic and endocrine correlates of variation in human sociality

Author: 
Date created: 
2017-06-06
Abstract: 

Hormones play evolutionarily ancient roles in social behaviour; yet the degree to which hormone systems influence human socio-emotional behaviour remains unclear. It is hypothesized that (i) hormone-associated genes linked to psychiatric conditions contribute to variation in social traits among non-clinical populations, and (ii) changes in endogenous hormone levels coordinate adaptive social behaviour with stimuli in the environment. Consistent with the first hypothesis, a vasopressin receptor polymorphism linked to autism was significantly associated with autistic-like traits in healthy individuals. Consistent with the second hypothesis, an empathy-inducing stimulus was found to mediate a trade-off in hormone levels, with oxytocin increasing and testosterone decreasing. Furthermore, a common polymorphism in the general transcription factor II-I gene, which is linked to Williams syndrome, was associated with oxytocin response to the empathy-inducing stimulus and social anxiety among healthy individuals. Together, these findings highlight the diverse ways through which hormone systems contribute to variation in human sociality.

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

The role of AfKDNase in the growth and development of Aspergillus fumigatus

Author: 
Date created: 
2017-04-18
Abstract: 

Aspergillus fumigatus is a filamentous fungus that is the most common cause of life-threatening invasive mould infections in immunosuppressed individuals. A. fumigatus produces a sialidase enzyme that shows a preference for 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid, (KDN). Sialidases break the glycosidic bond between terminal sialic acids and an underlying glycan chain. The purpose of my research was to create and characterize the KDNase knockout and complemented strains in A. fumigatus. Both strains were successfully generated. Growth in the presence of cell wall stressors (hyperosmolarity, antifungal agents, Congo Red dye) showed that the KDNase gene deletion affected morphology and cell wall integrity. Treatment of A. fumigatus conidia with endogenous AfKDNase enzyme resulted in conidial clumping and damage, an effect not observed when conidia were treated with a bacterial sialidase. The Δkdnase strain remained virulent in an immunosuppressed murine model of invasive aspergillosis.

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

Life histories and brain evolution of sharks, rays, and chimaeras

Author: 
Date created: 
2017-03-03
Abstract: 

The brain is perhaps one of the most fundamental organs in all vertebrates. It determines not only an individual’s ability to sense and process stimuli from the environment, but is also crucial in maintaining internal homeostatic processes as well as determining an individual’s cognitive abilities. Brains come at a steep energetic cost however, with neural tissue requiring ~20 times the energy of muscle tissue. With such an important role to play, the ‘expensive brain hypothesis’ was been established to understand the evolutionary correlates of brain size. Maternal investment, defined as energetic investment during development, is a strong underlying factor in brain size evolution where higher energy investment from mothers is associated with increased brain size. However, much of what we know about brains comes from studying birds and mammals, while generally overlooking other vertebrate classes. Despite their diversity, all jawed vertebrate brains are comprised of similar components, a pattern that first appeared in sharks, rays, and chimaeras (Chondrichthyans). Chondrichthyans are often disregarded as unremarkable from a comparative perspective, which overlooks their true diversity of life histories and ecological niches. This thesis seeks to understand the evolution of brain size and organization in relation to life history and maternal investment using chondrichthyans as a model system. First, I reveal the sequence of reproductive evolution, finding that egg-laying is ancestral and that live-bearing and additional maternal investment (matrotrophy) have evolved independently several times, and are correlated with increasing body size. Second, I find that the evolution of reproductive mode and ecological lifestyle underlie the evolution of both brain size and brain organization, such that shallowwater matrotrophic species have large brains that are predominantly composed of regions related to enhanced cognitive abilities, the telencephalon and cerebellum. Conversely, deepwater lecithotrophic species have small brains composed predominantly of medulla oblongata. Lastly, I find that similar patterns of regional scaling in mammals, birds and chondrichthyans differ from those of teleosts, agnathans, and amphibians, and I propose that differing reproductive strategies may underlie this variation.

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