Plasticity as a Sign of Developmental Bias in the Evolution of Gene Regulatory Networks

Phenotypic plasticity is an organism's ability to produce a different phenotype in response to nongenetic perturbations such as environmental disturbances. Beneficial phenotypic plasticity can be important in evolution. After an environmental disturbance, it can delay extinction giving opportunity to the appearance of beneficial mutations. In addition, plasticity may also be one of the factors that define the course that evolution takes, for example, through genetic assimilation. This is a process in which a phenotype that initially appears as a plastic response becomes under genetic control. In the end, development of such a phenotype does not require the factor that originally induced it. Here, I use a model of the evolution of gene regulatory networks to study the range of conditions that allow the association between plasticity and the course of evolution. I assayed conditions like the difference between ancestral and optimum phenotypes, the difficulty to build the optimum phenotype, the complexity of the developmental system, mutation rate, strength of plasticity limitations, fitness advantage of the optima, and the similarity between the initially induced phenotype and the optimum. I found that populations that yield a beneficial phenotype through plasticity most often evolve a similar genetically determined phenotype under all the conditions that I assayed. I also identified conditions that facilitate evolution through genetic assimilation. Notwithstanding, even under less favorable circumstances, this form of evolution still confers easier access to a new genetically determined optimum.