The evolution of reversible plasticity in stable environments

Phenotypic plasticity – the capacity of a genotype to develop into different phenotypes depending on environmental inputs – is widespread in nature. Although the construction of phenotypes is often the focus of research, many animals are also able to deconstruct phenotypic adjustments. Organisms routinely use such reversible plasticity to adjust to changes in their social or physical environment. For example, various invertebrates are able to deconstruct defensive morphologies previously built to defend against predators. Theory that explores the selection pressures favoring reversibility is scarce. Existing theory has almost exclusively focused on traits that develop instantaneously rather than incrementally, as is common with many morphological traits. Here, we present a model of the evolution of reversible plasticity when organisms develop incrementally. In our model, organisms repeatedly sample cues to infer the environmental state – which varies between generations but is stable across the lifetime – and incrementally adjust their phenotype to match their environment. Organisms have the possibility to deconstruct phenotypic adjustments. We assume two different modes of phenotypic deconstruction: Organisms can either deconstruct phenotypic adjustments incrementally or completely deconstruct all phenotypic adjustments in one time period. We highlight two results. First, while plasticity in construction is typically highest early in ontogeny, the highest levels of plasticity in deconstruction typically occur in mid-ontogeny. Second, contrasting previous models, we find that reversibility evolves frequently in stable environments and in species with shorter lifespans. Our model thus shows that reversibility does not require environmental change. Rather, reversibility may be favored when organisms are uncertain about the environmental state because the environment can change across generations. Our work illustrates the capacity for reversibility in species who experience environmental changes for the first time in their lives.