Scaling fitness optima-Studying adaptive evolution with multiple genotypes of Aspergillus nidulans

Abstract

Adaptation involves the successive substitution of beneficial mutations by selection, a process known as an adaptive walk. Theoretical models of adaptation have made predictions regarding the properties of adaptive walks, but we know little empirically about how adaptation differs between different genotypes faced with the same environment, knowledge that is critical to a broad understanding of natural adaptation. Furthermore, as the body of theoretical knowledge continues to grow, it is becoming apparent that the conventional model systems used to study adaptation, chiefly single-celled organisms, are not well-suited for studying adaptation in spatially structured environments, and, barring yeasts, cannot be used to study the effects of sex on adaptation. This thesis tackles both questions using the fungus Aspergillus nidulans , first demonstrating that the selection coefficients of mutations, but not the total number, are affected by initial adaptedness to an environment and then developing a mathematical growth model that will allow for further development of theoretical models of adaptation in spatially structured environments.