Phenotype selection due to mutational robustness

The mutation-selection mechanism of Darwinian evolution gives rise not only to the adaptation to environmental conditions but also to the enhancement of the robustness against mutation. Suppose more than one phenotypes share the same fitness value. The robustness distribution should differ for different phenotypes. Thus, we expect that some phenotype is favored in evolution and some is hardly selected as a consequence of the selection bias for mutational robustness. In this paper, we investigated this selection bias on phenotypes for a model of gene regulatory networks (GRNs) by numerical simulations. The model we used exhibits three types of response to the change of input signal; monostable, toggle switch, and one-way switch. We regarded these three response types as three phenotypes. We constructed the randomly generated set of GRNs using the multicanonical Monte Carlo method and compared it to the outcomes of evolutionary simulations. The results suggest that the one-way switches were strongly suppressed in evolution because a majority of the one-way switches were not mutationally robust.