CONVERGENCE AND DIVERGENCE OF ADAPTIVE STRATEGIES IN EXPERIMENTALY EVOLVING POPULATIONS OF SACCHAROMYCES CEREVISAE

Adaptation to an environment occurs through an increase of fitness. Fitness has several components that are classically called life-history traits. Because selection can not optimize all traits together, trade-offs arise between life-history traits and there are several ways, also called life-history strategies, to increase the fitness. Although the process of adaptation has been intensively studied since the first work of Darwin, we are still unable to predict which life-history strategies will evolve in which environment and which trajectories will be taken to reach the fittest life-history strategy. In this work we have studied how yeast life-history strategies evolved in a laboratory experimental evolution. We investigated the phenotypic evolution of six initially genetically and phenotypically different strains of Saccharomyces cerevisiae under four selection regimes. After over 260 generations, life-history strategies were studied using a multivariate analysis on nine life-history and four metabolic traits. We find that diversifying selection occurred between the four selection regimes but that there was phenotypic convergence for multiple traits within the selection regimes. The intensity of selection proved to be significantly dependent on the glucose composition of the medium. The degree of specialization depended both on the initial genetic background of the strains and on the environmental factors acting as selective agents. To our knowledge, this laboratory evolution experiment is the first one to analyze multitraits evolution for several genotypes in several environments.