Agent-based modelling of a nematode system provides general insights into the evolutionary constraints and modulators of phenotypic plasticity, bet-hedging, and environmental homeostasis

In this study, I implemented an agent-based model aimed at exploring the competition between plastic and non-plastic genotypes in a digital environment with periodic fluctuations in food resources, using the dimorphic nematode Pristionchus pacificus as a proxy for mixed-strategy systems showing a combination of stochastic and conditional phenotype production. Emerging behaviours generated in response to variation in three main variables, that is, i) intrinsic cost of plasticity, ii) timescale of environmental fluctuation, and iii) degree of plasticity, were monitored in terms of frequency and time to fixation of two alleles of the developmental switch gene eud-1, one enabling mouth-form dimorphism and predation, the other leading to the constitutive expression of a single, bacterivorous morph. Interestingly, while intermediate-to-long periods of environmental stability (in terms of generations) and a higher level of plasticity might favour the evolution of plastic strategies in a "cost-free" condition, the introduction and increase of inherent costs of plasticity could make pure bet-hedging more advantageous, induce a sequential collapse in the frequency of fixation of plastic strains and time of coexistence between strains, and make the invasion by non-plastic mutants more likely until a plateau is reached. In addition, asymmetries in fitness between the two morphs might be an almost necessary condition to enable the invasion of a non-plastic population by plastic genotypes. Collectively, while confirming some previous theoretical findings, these outcomes could uncover the sensitivity of a mixed-strategy system to even small changes in key variables, suggesting the existence of phase transitions and critical evolutionary constraints.