http://hdl.handle.net/1974/755 2013-05-24T21:41:00Z http://hdl.handle.net/1974/7878 Title: A paleolimnological assessment of recent environmental changes in lakes of the western Canadian Arctic Authors: THIENPONT, Joshua Abstract: The freshwater ecosystems in the western Canadian Arctic are threatened by multiple and interacting stressors, as high-latitude regions are undergoing rapid change resulting from climate warming and other human-related activities. However, due to the paucity or absence of monitoring data, little is known about long-term changes in lake ecosystems. This thesis addresses this knowledge gap by using paleolimnological techniques to assess the responses of freshwater ecosystems in the Mackenzie Delta region to three major stressors predicted to become increasingly important, namely impacts from accelerated permafrost thaw, marine storm surges, and hydrocarbon exploration. Using a paired-lake design, six reference lakes were compared to six lakes impacted by retrogressive thaw slumps, an important form of thermokarst in this region. While all of the study lakes have undergone ecologically significant biological changes over the last ~200 years as a result of warming, lakes impacted by thaw slumps have changed more due to the cumulative effects of warming and heightened permafrost thaw. In addition to warming, the outer Mackenzie Delta is a low-lying landscape that is susceptible to inundation by marine storm surges from the Beaufort Sea. A large storm event in 1999 flooded >10,000 hectares of the outer delta. My paleolimnological data show that this marine intrusion resulted in diatom assemblage changes in flooded lakes on a landscape-scale that were unprecedented in the recent past, suggesting recent warming, and associated sea-ice decreases, are making this region more susceptible to storm-surge damage. Finally, lakes impacted by sumps used to dispose of the drilling by-products of hydrocarbon exploration exhibit distinct water chemistry, and are particularly elevated in potassium and chloride, which form a major component of some drilling fluids. Related to this, a discernible change in cladoceran assemblages coeval with the time of sump construction suggest that sump failure has resulted in biological changes in affected lakes. Collectively, this research shows that the ecosystems of the western Canadian Arctic are under threat from multiple stressors that have resulted in changes to the chemistry and biology of the freshwater resources of this region. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-04-17 09:30:14.671 2013-04-17T04:00:00Z http://hdl.handle.net/1974/7857 Title: Linking courtship behaviour, colour perception and mate choice decisions in peafowl Authors: Dakin, Roslyn Abstract: Despite a long history of study showing that male courtship signals influence female mate choice in many species, we lack a good understanding of how females choose. What are the mechanisms of mate choice, and how do these mechanisms shape the evolution of courtship signals and traits? In this thesis, I use the peacock’s iridescent eyespots to link signal perception with female mate choice decisions and the behaviours males use during courtship. I begin by investigating how a peacock’s eyespot colours influence his mating success, using models of avian colour vision and measurements of eyespot plumage colours taken at light angles that mimic the way the feathers are displayed during courtship. My results suggest that a substantial portion of the variation in peacock mating success can be explained by these plumage colours, demonstrating that signal function is best understood by considering the context in which signals are presented. Next, I examine how females choose to visit different males for courtship. I show that a female’s familiarity with a male as a result of previous courtship encounters affects how she responds to his signals, including his eyespot colours. Lastly, I examine the visual effects of the peacock’s iridescent eyespot colours under different light conditions, and show that typical male courtship behaviours might enhance the eyespots in a way that influences female choice. I also find evidence that light conditions and female sensory biology together may have shaped the evolution of the eyespot colours in two species of peafowl. Overall, the results of this thesis demonstrate that by understanding how animals perceive colour signals, we can gain a better understanding of the function of behaviour on both sides of the courtship signaling exchange. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-03-22 14:23:48.991 2013-03-25T04:00:00Z http://hdl.handle.net/1974/7841 Title: Contact zone dynamics and the evolution of reproductive isolation in a North American treefrog, the spring peeper (Pseudacris crucifer) Authors: Stewart, Kathryn Abstract: Despite over seven decades of speciation research and 25 years of phylogeographic studies, a comprehensive understanding of mechanisms that generate biological species remains elusive. In temperate zones, the pervasiveness of range fragmentation and subsequent range expansions suggests that secondary contact between diverging lineages may be important in the evolution of species. Thus, such contact zones provide compelling opportunities to investigate evolutionary processes, particularly the roles of geographical isolation in initiating, and indirect selection against hybrids in completing (reinforcement), the evolution of reproductive isolation and speciation. The spring peeper (Pseudacris crucifer) has six well-supported mitochondrial lineages many of which are now in secondary contact. Here I investigate the evolutionary consequences of secondary contact of two such lineages (Eastern and Interior) in Southwestern Ontario using genetic, morphological, acoustical, experimental, and behavioural evidence to show accentuated divergence of the mate recognition system in sympatry. Mitochondrial and microsatellite data distinguish these two lineages but also show ongoing hybridization. Bayesian assignment tests and cline analysis imply asymmetrical introgression of Eastern lineage nuclear markers into Interior populations. Male calls are divergent between Eastern and Interior allopatric populations and show asymmetrical reproductive character displacement in sympatry. Female preference of pure lineage individuals is also exaggerated in sympatry, with hybrids showing intermediate traits and preference. I suggest that these patterns are most consistent with secondary reinforcement. I assessed levels of post-zygotic isolation between the Eastern and Interior lineages using a laboratory hybridization experiment. Hybrid tadpoles showed equal to or greater fitness than their pure lineage counterparts, but this may be countered through competition. More deformities and developmental anomalies in hybrid tadpoles further suggest post-zygotic isolation. Despite evidence for pre-mating isolation between the two lineages, isolation appears incomplete (i.e. hybridization is ongoing). I hypothesize that potentially less attractive hybrids may circumvent female choice by adopting satellite behaviour. Although mating tactics are related to body size, genetic status may play a role. I show that pure Eastern males almost always engage in calling, while hybrids adopt a satellite tactic. An absence of assortative mating, despite evidence of female preference, suggests successful satellite interception possibly facilitating introgression. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-03-04 16:01:33.892 2013-03-04T05:00:00Z http://hdl.handle.net/1974/7809 Title: A ROLE FOR INSULIN SIGNALING IN REGULATING THE PTEN TUMOUR SUPPRESSOR IN CAENORHABDITIS ELEGANS Authors: LIU, JUN Abstract: Many obese individuals and type 2 diabetes mellitus (T2DM) patients have elevated levels of insulin. Hyperinsulinemia is a major cancer risk factor in T2DM individuals and activated insulin receptor (IR) has been linked to many types of cancer and poor survival. However, the mechanisms that account for the link between the hyper-active insulin signaling and cancer risk is not well understood. PTEN plays an antagonistic role in the canonical insulin signaling pathway, and is the second most commonly mutated tumour suppressor (after p53) found in human cancers. In many cancers the PTEN gene is not deleted, but instead the protein is lost. Therefore the regulation of PTEN protein in humans is of great importance. Here we hypothesized that the activated insulin signaling down-regulates PTEN. Considering that insulin signaling is highly conserved from C. elegans to human, I used C. elegans as a model and showed that DAF-2, the worm homolog of IR, is a negative regulator of DAF-18, the worm homolog of PTEN. In addition, I showed that DAF-28, the worm homolog of insulin, also negatively regulates DAF-18/PTEN. I used western blot and immunostaining to show that the protein level of DAF-18/PTEN is increased in the daf-2/IR and daf-28/insulin mutants. I further showed that daf-18/Pten is genetically epistatic to daf-2/IR in regulating neuronal development. I then employed human cell culture experiments and reported that this negative regulation is conserved in human cancer cell lines. I showed that knocking-down IR through siRNA up-regulates PTEN, and over-expressing a gain-of-function IR down-regulates PTEN. I also showed that insulin stimulation dramatically decreased PTEN and this decrease is dependent on IR. I further confirmed a physical association between IR and PTEN in both human and C. elegans, and reported that IR could phosphorylate PTEN. To provide mechanistic insight to DAF-18/PTEN regulation, I identified another protein, which is a ubiquitin ligase, that functions in insulin signaling to down-regulate DAF-18/PTEN. Additionally, I also provided evidence that insulin signaling cross talks with Eph receptor signaling. In summary, my findings will be informative for cancer biologists to study the roles of these genes in carcinogenesis. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-02-04 14:37:29.376 2013-02-05T05:00:00Z