Small change? : adaptation and its costs, in experimental evolution

Abstract

Trade-off is an important feature of theory concerning adaptation across environments. This thesis develops concepts and tests theories concerning trade-offs, using tools from experimental microbial evolution in the yeast Saccharomyces cerevisiae. Data used includes variants from whole genome sequencing and phenotypic data from Biolog TM multi-well plates. Both of these techniques were used to analyse populations from previous experiments over 300 generations of adaptation in chemostat and serial transfer conditions conducted by Jeremy Gray and Matthew Goddard. It is shown that sexual status impacts on molecular evolution, changing the spectrum of variants observed in adapting populations. Mutation rate and sexual status are also shown to play a role in shaping the evolution of phenotypic trade-offs across environments, and groundwork is laid for future research in this area, using the increasingly accessible tools for high throughput microbial population research. This work also contributes to theory in the field. It is argued that trade-off model in biological systems is correlated with genomic complexity, and that antagonistic pleiotropy is the dominant mechanism of trade-off for microbes under ‘normal’ conditions, such as in the absence of a mutator phenotype. Theory concerning trade-off and adaptation is also briefly applied to issues underlying the development of antibiotic resistance in bacterial populations.