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, and 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 is
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.