Evolution of multicellularity and unicellularity in yeast S. cerevisiae to study reversibility of evolutionary trajectories.

Abstract

Adaptive trajectories of populations have been focus of number of studies. However, adaptive trajectories have not been studied in the context of reverse evolution. By reverse evolution, we mean a scenario where selection is reversed. In this work, we use evolution (and reversal from) of multicellularity in S. cerevisiae as a model to answer this question. When selected for fast-settling variants, multicellularity evolves rapidly in the organism. On reversing selection, unicellularity evolves from the multicellular clusters. However, the dynamic trajectories of the two processes are different. In this context, evolution is not reversed dynamically at a phenotypic level. The phenotypic reversal is not driven by reversal of the original mutations during the forward evolution. Overall, our results show that the dynamics of molecular and phenotypic trajectories of evolution are distinct, and reversal of selection leads to unique trajectories of phenotypic reversal.