Effects of Phenotypic Plasticity and Unpredictability of Selection Environment on Niche Separation and Species Divergence

Evolution of a phenotypically plastic trait is examined under weak optimizing selection in a heterogeneous environment. Selection operates toward optimum phenotype that depends upon the environment. Density-dependent number regulation is caused by nonuniform food supply. The juveniles do not disperse but develop in the parental patch. An adult has a certain probability to migrate to a different patch of selection. Density-dependent number regulation operates after selection. There is one Gaussian food distribution over the patches for a haploid population. The model is individual based. A mutation model has been developed to find the evolutionary stable strategies genotypic values. In the absence of phenotypic plasticity, multiple populations are observed at evolutionary equilibrium with clear niche separation. The genotypes are specialists. Splitting of the population occurs beyond a critical value of food width (defined as the food distance between patches where food supply is half of the maximum value) at fixed migration width. This critical value is correlated with migration distribution. The genotypes develop generalist tendency with the increase of the level of plasticity. Eventually genetic differentiation is removed and one population is found at equilibrium beyond a critical value of plasticity. The genotypes become generalists. Phenotypic plasticity increases niche width and tempers niche separation. The critical value of food width increases with higher migration width. Phenotypic plasticity allows niche separation in the presence of two Gaussian food distributions if the food width happens to be below a critical value and the food distance between the peaks of the two Gaussian food distributions lies above a threshold range. In the presence of additive allelic effect of a diploid population, polymorphic state is observed in the presence of phenotypic plasticity. An initially monomorphic population evolves into two genotypically diverging lineages. The local abundance of food causes local genotypic specialization leading to polymorphism. Niche separation becomes easier with higher selection intensity. © 2019 Elsevier B.V.