A thesis submitted to the school of graduate studies in the partial fulfillment of the requirements for the degree doctor of philosophy. / Fungal populations occupy a vast number of ecological niches across many geographic areas around the planet. Fungi act as essential nutrient recyclers, playing key roles as saprophytes, mutualists, and pathogens. As humans, we use these broad properties of fungi in biochemical and pharmaceutical industries, creating a plethora of products ranging from antimicrobials to food products. However, certain fungal species have become a devastating burden on human public health. Of these fungal species, my PhD thesis has focused on the critically important mold Aspergillus fumigatus. This mold is an opportunistic human pathogen, being the leading etiological cause of the spectrum of diseases termed aspergillosis that yearly affects over 8,000,000 people worldwide. In addition, the rising number of antifungal resistant strains around the world, especially within environmental populations, is of critical concern. Given that almost all aspergillosis infections result from environmental strains, and that soil is a major ecological niche for A. fumigatus, my thesis focused on characterizing genetic and phenotypic aspects of soil isolates of A. fumigatus obtained from many geographic and climatic regions around the world. My analyses revealed extensive allelic and genotypic diversity within and among populations. These A. fumigatus populations were defined by both historical differentiations, high gene flow, non-random recombination, and high susceptibility to triazole antifungals. Additionally, I tested the sexual fecundity of a subset of these global strains and found that geographic and genetic distance between the pairs of parental strains had little effect on sexual fecundity. Lastly, my research found broad variations in growth of a global sample of A. fumigatus strains at different temperatures. Again, no relationship of either geographic or genetic distance on strain growth was observed. Overall, my research highlights the extraordinary nature of A. fumigatus populations to quickly spread and adapt across diverse and complex environments. / Thesis / Doctor of Philosophy (PhD) / Aspergillus fumigatus is a cosmopolitan mold that causes opportunistic infections in humans termed aspergillosis. To better understand the environmental reservoirs of aspergillosis infection, I investigated soil populations of this fungus, as soil is likely the largest reservoir of A. fumigatus. I isolated A. fumigatus strains from 11 countries across 6 continents and genetically compared these soil populations to each other and to clinical A. fumigatus populations. I found extensive genetic diversity within most local soil populations, along with different relationships among geographic populations. When a sample of these global strains were sexually crossed, I uncovered high variation in their sexual fecundity, which lowered at higher geographic distances. Lastly, strains exhibited high variations in growth at different temperatures regardless of climatic, genetic, and geographic factors from where they were isolated. My thesis highlights the extraordinary phenotypic variations and complex population structure of A. fumigatus populations isolated from soil across the globe.

Over the last 100 years sexual selection has advanced into a vast field of theoretical and empirical research. While Darwin’s idea of female preference being an integral mechanism of sexual selection is no longer debated, our understanding of female preference is still very limited. For example, we know little about the genetic variation in female preference, and the costs of preference over and above the costs of mating with particular male phenotypes. Additionally, while costs of mate choice are well documented, the benefits of mate choice and their implications are still debated. For example, controversy exists over the inevitability of good gene benefits and their capability to promote adaptive sexual selection. Furthermore, the adaptiveness of sexual selection itself is debated. Our understanding of the traits involved in mate choice is also far from complete. Here I investigated aspects of sexual selection in Drosophila simulans, employing a range of behavioural approaches along with artificial selection and environmental manipulations. The findings presented here indicate that female preference can evolve when directly selected on, and that preference itself is not particularly costly. There was also no conclusive evidence for the good genes benefits of mate choice in D. simulans. These benefits are considered crucial in promoting the adaptiveness of sexual selection, and although we found sexual selection to be adaptive under some test conditions it was not adaptive in other conditions. Our investigations into traits involved in mate choice established sex-specific genetic variation in cuticular hydrocarbons and the genetic architecture of this trait was found to sex-specific evolution of cuticular hydrocarbons under natural and sexual selection. Additionally, we found that a secondary sexual character, the sex combs was positively allometric – just like most signalling and weapon traits, and there was no association between trait fluctuating asymmetry and trait size. These findings collectively indicate that sexual selection in D. simulans is consistent with classical models of this process.