  Non-genetic perturbations, such as environmental change or developmental
noise, can induce novel phenotypes. If an induced phenotype confers a fitness
advantage, selection may promote its genetic stabilization. Non-genetic
perturbations can thus initiate evolutionary innovation. Genetic variation that
is not usually phenotypically visible may play an important role in this
process. Populations under stabilizing selection on a phenotype that is robust
to mutations can accumulate such variation. After non-genetic perturbations,
this variation can become a source of new phenotypes. We here study the
relationship between a phenotype's robustness to mutations and a population's
potential to generate novel phenotypic variation. To this end, we use a
well-studied model of transcriptional regulation circuits. Such circuits are
important in many evolutionary innovations. We find that phenotypic robustness
promotes phenotypic variability in response to non-genetic perturbations, but
not in response to mutation. Our work suggests that non-genetic perturbations
may initiate innovation more frequently in mutationally robust gene expression
traits.
