Data from: The robustness and evolvability of continuously-varying traits

Theoretical work on the evolution of simple phenotypes with discrete
states, such as RNA and protein structures, has shown that the most
evolvable phenotypes have intermediate levels of mutational robustness, so
long as we let neutral mutations cause the diversification of a
population’s mutationally-accessible phenotypic neighborhood. But whether
this applies to more complex phenotypes is unclear. Here, I predict that
for quantitative traits, intermediate levels of mutational robustness
should boost evolvability whenever (i) the adaptive landscape changes
after a period of stabilizing selection, and (ii) the phenotypic
neighborhood of a genotype is determined in large part by the accumulation
of cryptic alleles, the effects of which can be exposed to selection by
epistatic mutations. I present evolutionary simulation models that support
these predictions, provided that cryptic allele effects are not too large.
Genetic diversity can also be concealed and exposed by incomplete
environmental robustness (i.e., plasticity). With additional simulations,
I show that evolvability can also be maximized with intermediate levels of
environmental robustness, although in a more restrictive parameter space.
So, as for discrete traits, quantitative trait robustness can be good for
evolvability.