Molecular characterization of clonal interference during adaptive evolution in asexual populations of Saccharomyces cerevisiae

The classical model of adaptive evolution in an asexual population postulates that each adaptive clone is derived from the one preceding it1. However, experimental evidence suggests more complex dynamics2-5 with theory predicting the fixation probability of a beneficial mutation as dependent on the mutation rate, population size, and the mutation's selection coefficient6. Clonal interference has been demonstrated in viruses7 and bacteria8, but has not been demonstrated in a eukaryote and a detailed molecular characterization is lacking. Here we use different fluorescent markers to visualize the dynamics of asexually evolving yeast populations. For each adaptive clone within one of our evolving populations, we have identified the underlying mutations, monitored their population frequencies and used microarrays to characterize changes in the transcriptome. These data provide the most detailed molecular characterization of an experimental evolution to date, and provide direct experimental evidence supporting both the clonal interference and the multiple mutation models. In his seminal paper in 1932, Muller proposed that in asexual populations, adaptive events occur in succession1. This now classical model of evolution by clonal replacement has bee