The evolution of reversible plasticity in stable environments.

Reversible plasticity, i.e., the ability to deconstruct phenotypic specializations based on environmental conditions, is widespread in nature. Despite its ubiquity, few mathematical models have explored the evolutionary selection pressures that favor trait reversibility. Therefore, many scenarios remain to be examined. In particular, existing theory has modeled trait development as an instantaneous process. These models do not capture the fact that trait development is often a constructive process, in which phenotypes incrementally adjust to local ecologies. Here, we present an optimality model of the evolution of reversible plasticity in which organisms build traits incrementally. In our model, organisms repeatedly sample cues to infer the environmental state-which can vary between generations but not within generations-and incrementally tailor their phenotypes to match their environments. Organisms also have the option to deconstruct phenotypic adjustments. We investigate 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, early-life sensitive periods in construction precede mid-ontogeny sensitive periods in deconstruction. Intriguingly, although organisms typically only deconstruct toward the end of ontogeny, environmental cues in mid-ontogeny have the strongest impact on deconstruction. Second, in contrast to previous models, we find that reversibility often evolves in environments that are stable within generations. Thus, our model shows that reversibility does not require environmental change during development-as long as organisms are initially uncertain about environmental conditions. Our model provides new insights into the capacity for reversibility in species that have evolved in ontogenetically stable environments.