Candida albicans, the most prevalent human fungal pathogen, demonstrates remarkable adaptability and genome plasticity, enabling it to thrive in diverse environments within the human body. This pathogen unequivocally serves as a common commensal member of the human microbiota and poses as an opportunistic pathogen capable of causing infections under specific conditions. The C. albicans genome can undergo significant alterations, including single nucleotide polymorphisms, insertions, deletions, and chromosomal aneuploidy, particularly under environmental stresses such as exposure to azole drugs like fluconazole. This thesis examines crucial aspects of microbial competition and the evolutionary dynamics of C. albicans under drug stress, particularly fluconazole. Competitive fitness, a fundamental concept in evolutionary biology, measures organisms' ability to survive, reproduce, and compete for resources. Traditional methods for assessing microbial competitive fitness are labour-intensive and involve manual colony counting. Chapter 2 introduces a high-throughput, automated method that employs fluorescent microscopy and machine learning to measure head-to-head competition between microbial populations quantitatively. This innovative approach significantly enhances the accuracy and reproducibility of fitness assessments. Fluconazole is a widely used antifungal agent that has been shown to induce resistance in C. albicans through repeated use. Previous studies on fluconazole tolerance and resistance have largely focused on high population sizes where selection pressure is prominent. This thesis pioneers examining mutation accumulation and evolutionary responses of C. albicans at low population sizes, where genetic drift plays a more substantial role. In Chapter 3, I have evolved replicate lines of C. albicans through mutation accumulation experiments in both the presence and absence of fluconazole, followed by comprehensive phenotypic and genotypic analyses. The results indicate that C. albicans lines evolved without fluconazole showed no significant changes in fitness compared to ancestral lines. In contrast, lines exposed to fluconazole showed a significant, dose-dependent increase in drug tolerance, competitive fitness, and the prevalence of aneuploid chromosomes. These findings highlight the dual role of fluconazole in inducing and selecting advantageous mutations, driving rapid adaptation in C. albicans. This study underscores the profound impact of antifungal treatment on the evolutionary trajectories of pathogenic fungi and provides insights into the mechanisms underlying drug resistance.