Effects of Phenotypic Robustness on Adaptive Evolutionary Dynamics

Theoretical and experimental studies have provided evidence for a positive role of phenotype resistance to genetic mutation in enhancing long-term adaptation to novel environments. With the aim of contributing to an understanding of the origin and evolution of phenotypic robustness to genetic mutations in organismal systems, we adopted a theoretical approach, elaborating on a classical mathematical formalizations of evolutionary dynamics, the quasispecies model. We show that a certain level of phenotypic robustness is not only a favourable condition for adaptation to occur, but also a required condition for short-term adaptation in most real organismal systems. This appears as a threshold effect, i.e. as a minimum level of phenotypic robustness (critical robustness) below which evolutionary adaptation cannot consistently occur or be maintained, even in the case of sizably selection coefficients and in the absence of any drift effect. These results, are in agreement with the observed pervasiveness of robustness at different levels of biological organization, from molecules to whole organisms.