MODELING PHENOTYPIC PLASTICITY .1. LINEAR AND HIGHER-ORDER EFFECTS OF DOMINANCE, DRIFT, ENVIRONMENTAL FREQUENCY AND SELECTION ON A ONE-LOCUS, 2-ALLELE MODEL

The evolutionary dynamics of dominance, drift, selection and probability of environmental change is explored in the case of a single-locus two-allele model for the genetic control of phenotypic plasticity. The model represents a situation similar to the real case of the pennant/vestigial phenotype in Drosophila melanogaster. The aim of the simulation is to analyse the contribution of the four factors, of their quadratic effects, and of the two-way interactions on the equilibrium frequencies of the two alleles and on the genotypic constitution of the population. Selection turned out to be the only factor whose linear component significantly affects the system (73% of the variance explained); on the other hand, the cumulative effect of the nonlinear terms is strong (20% of the variance), and most of the interactions are highly significant. Some counter-intuitive effects of the interaction between selection and dominance or selection and frequency of the two environments are shown by means of contour plots from a multidimensional regression surface analysis. An interesting outcome is that plasticity can be favoured in a homogeneous environment, and it is selected against in one particular case of environmental heterogeneity: when two environments are equally likely to occur.