The molecular basis of phenotypic plasticity evolves in response to environmental predictability

Phenotypic plasticity, the response of a given genotype to its environment of development, is a ubiquitous feature of life, enabling organisms to cope with variation in their environment. Theoretical studies predict that, under stationary environmental variation, the level of plasticity should evolve to match the predictability of selection at the timing of development. However, we still lack critical empirical evidence on the extent to which selection on phenotypic plasticity cascades down from higher phenotypic levels to their underlying molecular basis. Here, we used experimental evolution under controlled environmental fluctuations, to test whether the evolution of phenotypic plasticity in responses to environmental predictability ( ρ 2 ) occurred across biological levels, going from DNA methylation to gene expression to cell morphology. Transcriptomic results indicate clear effects of salinity and ρ 2 ×salinity interaction on gene expression, thus identifying sets of genes involved in plasticity and its evolution. These transcriptomic effects were independent of DNA methylation changes in cis . However we did find ρ 2 - specific responses of DNA methylation to salinity change, albeit weaker than for gene expression. Overall, we found consistent evolution of reduced plasticity in less predictable environments for DNA methylation, gene expression, and cell morphology. Our results provide the first clear empirical signature of plasticity evolution at multiple levels in response to environmental predictability, and highlight the importance of experimental evolution to address predictions from evolutionary theory, as well as investigate the molecular basis of plasticity evolution.