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<p> This work incorporates information from two sources in order to examine the nature of natural selection acting on phenotypic characters in Drosophila melanogaster along a North South cline. Isofemale lines were established from flies collected along a North South cline extending from Winnipeg, Manitoba to Tampa Bay, Florida. Offspring from different lines within each position were then cultured under standardized conditions and used to examine phenotypic variation in 10 morphological characters along the cline. In a separate set of experiments, flies from Vineland, Ontario were mated in a half-sib design in order to estimate the genetic covariance of the set of 10 characters. The results from the clinal and heritability experiments were then combined using Lande's (1979) equation,&.= Gp-ls, to estimate the net selective differentials and net selection gradients for each adjacent set of populations. The study concluded that: 1) Clinal variation is non-linear, with larger flies in the middle latitudes and smaller flies in the north and south. 2) Selection appears to act primarily on body characters in the north (wing width and femur length) and head characters in the south (eye and face width). 3) Scutellum width and wing length generally moderate the prevalent trends in directional selection on the other characters through antagonistic correlated responses. 4) Clinal patterns of variation may not be at equilibrium, but instead dominated by seasonal responses to selection pressures. </p> / Thesis / Master of Science (MSc)

Strains of pathogens are typically described as virulent or non-virulent. However, in the majority of pathogens, strains often vary continuously and quantitatively in their virulence and pathogencity. Biofilm formation is one of the recently recognized virulence factors in many human pathogens and little is known about the variation and evolution of biofilms among natural strains. In this study, I examined quantitative variation of biofilms among natural strains of the human pathogenic yeast Candida albicans. A total of 115 natural strains of C. albicans from three sources (vaginal, oral and environmental) were quantified by two mebods: (i) the XTT tetrazolium reduction assay, and (ii) optical density following staining by crystal violet dye. Mature biofilm was confirmed by observation using confocal laser scanning microscopy. My analyses indicated that strains from each of the three scurces varied widely in biofilm formation abilities and that biofilm formation ability was positively correlated to cell surface hydrophobicity (CSH). For each strain, multilocus genotypes were determined by PCR-RFLP, my comparative genotype and biofilm analyses denonstrated that natural clones and clonal lineages of C. albicans exhibited extensive quantitative variation for biofilm formation. I also examined potential interactions among strains within C. albicans and between different Candida species. My preliminary results suggest significant variation and complex patterns of strains or species interaction during Candida biofilm development. / Thesis / Master of Science (MS)

Background dependence is a ubiquitous attribute of eukaryotic gene systems that modulates the phenotypic effects of a mutant allele due to segregating genetic variation among different wildtype strains. Despite the wealth of literature demonstrating the presence of genetic background effects, very little is known about how they functionally or mechanistically contribute to the relationship between genetic variation and phenotypic expression. It has been postulated that background dependent effects may be highly specific to the activity of individual alleles or genes. A recent examination of mutant alleles in two interacting genes in the Drosophila wing network demonstrated the magnitude of phenotypic effect of a mutant allele may predict it’s sensitivity to the genetic background. To further understand this, I examined the background dependence of many alleles for genes across the regulatory network of Drosophila wing development in many inbred strains. Our goal was to understand whether effects of the genetic background are an attribute of individual alleles, alleles of the same gene, or genes with similar phenotypes or developmental roles. Our analysis suggests that background dependence is highly positively correlated among alleles of the same gene, especially between alleles with similar magnitudes of phenotypic effect. Similarly, the background dependence of genes within the same regulatory network were also positively correlated. Alleles from different genes, but of the same magnitude of phenotypic effect, generally demonstrated the highest degree of intergenic correlation. However, the background dependence of mutant alleles were generally not well correlated with the wildtype allele. Interestingly, we also found no recovery of any lethal alleles, despite thousands of individuals screened and evident suppression of mutant effects in some strains. We also analyzed the magnitude of intra-line variance in among a subset of our genes. This demonstrated a strong positive relationship between the magnitude of intra-line variation and the severity of phenotypic effects, regardless of the identity of the mutant allele. However, we show no correlation between intra-line variability in the wildtype and the magnitude of perturbation for a given mutant allele. To confirm the quantitative estimates of mean wing size accurately reflected subtle perturbations to wing tissue, we conducted a semi-quantitative analysis and compared it to our quantitative estimates. We demonstrate a high degree of correlation between the quantitative and semi-quantitative approaches, indicating semi-quantitative analysis is a useful way to capture subtle phenotypic effects. In addition, we repeated the quantitative analysis with a subset of the genes and inbred strains from the original data. Importantly, results of the repeated study largely recapitulate our original results. / Thesis / Master of Biological Science (MBioSci)

Coastal environments are important in many ways: they provide food and energy for coastal communities, have a variety of unique biologic habitats, and influence global climate. These environments can change due to either anthropogenic or natural phenomena over a wide range of time scales. However, the often overlooked long-term (centennial to millennial) processes may be hidden behind short-term fluctuations observed today. The need for a reference baseline of coastal habitats provides a new opportunity for paleontology, which is ideally equipped to document the long-term trends and reconstruct historical and ancient environments and communities. However due to taphonomic processes such as decay and diagenesis, there will always be some bias inherent to the fossil record. This bias has been often viewed as a negative aspect, undermining the utility of paleontological data for retrieving ecological and environmental records. Yet, fossils are still one of the best sources of direct data about the past faunas and their ecosystems. To overcome the biases introduced by the fossilization process, researchers have used observations and experiments in modern systems as models to compare fossil deposits, a method called actualistic paleontology. Over recent years, such actuopaleontological approaches have been used increasingly to exploit distinct signatures of fossil deposits in environmental reconstructions, quantify effects of anthropogenic processes on invertebrate faunas and regional ecosystems, and even augment archaeological studies. Three studied included in this dissertation exploit different aspects of paleontological techniques to study coastal systems, including both Recent and fossil settings. Two of the studies use modern environments to serve as models for investigating preservation potential and potential biases that affect subfossil and fossil assemblages forming in intertidal environments, from whether certain fauna will be preserved to the biases inherent in a shell deposit. The final study, conducted at a fine geologic resolution, focuses on the morphology of a fossil ancestor of an extant mactrid bivalve that is ecologically important in many present-day coastal habitats and well-studied by ecologists and malacologists. The study attempts to quantify morphological effects of environmental changes that occur over geological time scales. / Ph. D.