Biosciences Research Seminar - Do deleterious mutations play a constructive role in phenotypic evolution?

Deleterious mutations are often purged from the population and are therefore generally considered to be irrelevant for phenotypic evolution. However, they could be compensated by conditionally beneficial mutations, thereby providing access to new adaptive paths. In this talk, I present evidence in favor of this hypothesis. Using high-dimensional phenotyping of laboratory-evolved budding yeast lineages we find that new cellular morphologies emerge exceptionally rapidly as a by-product of gene loss and subsequent compensatory evolution. Unexpectedly, the capacities for invasive growth, multicellular aggregation and biofilm formation also spontaneously evolve in response to gene loss. These ecologically and clinically relevant traits originate as pleiotropic side-effects of compensatory evolution and have no obvious utility in the laboratory environment. The extent of morphological diversity in the evolved lineages is comparable to that of natural yeast isolates with diverse genetic backgrounds and lifestyles. We conclude that compensatory evolution is a previously unrecognized source of morphological diversity and phenotypic novelties.