This project investigated the genetic composition of natural populations of Anadara trapezia in Australia at three spatial scales : i) microgeographic (within an estuary, 50 metres to ~ 6 kilometres); ii) microgeographic (within populations, less than 50 metres); and, iii) macrogeographic (hundreds of kilometres along the coast of Australia). Allozyme polymorphism surveys using cellulose acetate strips have revealed, from 43 enzymes screened, 18 putative polymorphic loci. Comparisons of levels of heterozygosity among enzyme structural groups showed no significant differences, however, monomers were significantly more variable as a group than multimers. Significant differences in the level and distribution of polymorphism among functional groups of enzymes were observed. It appears that selection may be acting at the molecular level, not only on a particular locus, but on a group of functionally similar loci. At the macrogeographic scale, significant departures from random mating were observed in most populations. Significant differences in allele distribution among populations of A. trapezia along the east coast of Australia were found. At the macrogeographic scale, heterogeneity of allele frequencies may depend upon the distance separating the populations and surface water currents. Differentiation among population groups in this study is attributed to changes in the direction of the East Australian Current combined with onshore countercurrents. The systematic status of the disjunct western Australian population of A. trapezia was also evaluated as compared with the east coast populations. No evidence of genetic, hence evolutionary divergence was found. The results have serious implications in the management of fisheries as erroneous assumptions in fisheries management models may lead to depletion and near extinction of marine species. The research stresses the necessity of sampling at multiple scales and replication strategies. It also highlighted the complexities researchers are faced with in studies of marine bivalves, such as the presence of null alleles, deficiencies of heterozygotes, apparent inbreeding and the small geographic scales governing population structure. / Doctor of Philosophy (PhD)

<p><strong><br /></strong></p> / <p><strong>In Canada the incidence of yeast infections have increased over the past decade, which in turn has resulted in the increased mortality and morbidity rates among the immuno-compromised patients. Yeasts are ubiquitous in nature and constitute a healthy portion of human skin and gut flora. Factors such as the urban settings and food have been previous shown to influence the yeast flora people harbour. This makes us believe that to effectively tackle the rising yeast infections in Canada we need to not only conduct epidemiological yeast studies in clinical settings but should also understand the diversity and distribution of them in the urban environment. This thesis constitutes of an epidemiological fungemia study and an urban environmental yeast profiling study conducted in the city of Hamilton.</strong></p> <p><strong> </strong></p> <p><strong>In the first chapter of the thesis I discuss the results of the epidemiological candidemia study. We noticed that over the past decade the mean age of the population with candidemia in hospitals within Hamilton has increased by 10 years. DNA fingerprinting analysis suggested that 33% of the blood stream</strong><strong><em>Candida</em></strong><strong> </strong><strong>isolates from January 2005 to February 2009 belonged to 18 clusters, some of which were shared between wards and hospitals. we found that for each of the four species, strains isolated closer to each other temporally were overall genetically more similar to each other as well, which suggested that nosocomial sources likely caused repeated candidemia infections. The study is the first of its sort in Canada and the results of this chapter are expected to aid infection control practitioners in the Hamilton hospitals and make the stay of patients in hospitals safer.</strong></p> <p><strong> </strong></p> <p><strong>In the second chapter, we discuss the diversity and distribution of yeasts prevalent on trees in and around Hamilton. We identified a total of 88 environmental yeasts belonging to 20 species (based on ITS sequence data). The yeast populations were highly heterogeneous in both species and genotype composition. Among the 14 tree species sampled, yeasts were frequently found on cedar, cottonwood and basswood. Interestingly all the</strong><strong> <em>Candida parapsilosis</em> </strong><strong>strains were found from pine tree only. Some of the potential environmental factors shaping the distribution of yeast populations in Hamilton are discussed.</strong></p> / Master of Science (MSc)