Sex decreases the pleiotropic costs of local adaptation by purging hitchhiking load

Understanding the evolutionary mechanisms that maintain sex despite its direct costs is a long-standing challenge. Previous work has shown that sexual recombination can accelerate adaptation, in part by separating beneficial mutations from deleterious hitchhikers. However, earlier studies focused on effects of sex in a constant environment. We show that recombination provides an advantage during changing conditions in promoting the evolution of generalist phenotypes by reducing pleiotropic costs caused by local adaptation. Using laboratory evolution in Saccharomyces cerevisiae , we show that hitchhiking load leads to pleiotropic costs and hence specialization in response to local adaptation in asexual but not sexual lineages. This provides evidence that sex can be maintained over long evolutionary timescales because it enables lineages to persist in the face of environmental change.