How does robustness affect evolvability?

Here, by consolidating and extending simple models of how genetic robustness affects the evolvability of phenotypes with discrete states, I uncover three new insights. (i) Environmental robustness can boost evolvability by allowing populations to spread across a migrationally neutral network of demes, thereby increasing the diversity of plastic phenotypes that can be accessed by migration. (ii) Counter-intuitively, when adaptive landscapes are complex, an increase in environmental stability can increase the frequency of environmentally robust but mutationally sensitive genotypes. This appears to be due to relaxed selection for mutational robustness in generalists. (iii) Evolvability can be affected by changes in mutational sensitivity, or by changes in the neighborhood of phenotypes accessible by non-neutral mutations. Because it allows for the evolution of increased evolvability without a concomitant increase in genetic load, selection should favor changes in the phenotypic neighborhood over changes in mutational sensitivity. Moreover, with fluctuating selection, the potential gains in evolvability conferred by increased mutational sensitivity can be diminished by selective sweeps on the phenotypic neighborhood.