4 Synthesis: when does plasticity help or hinder adaptive evolution?
Climate change will lead to changes in the rate, variation, and autocorrelation of environmental variables. Moving optimum theory provides a mechanistic approach to develop hypotheses about the impact of plasticity on adaptive evolution in different environments. It is clear that hypotheses such as the Bogert effect, Plasticity-First, and Baldwin hypothesis cannot be tested without controlling for the types of environmental change. This is because the facilitative role that plasticity might play for adaptive evolution in the face of environmental change depends on how the environment is changing. Each of the three environmental components (Fig. 1) influences the two broad categories of eco-evolutionary response mechanisms: 1) heritability, genetic variation, and selection, and 2) within-generation plasticity and population dynamics. The interaction between environmental change components and response mechanisms produces a rich breadth of hypotheses (Box 1); empirical and theoretical tests of these hypotheses will form a more integrative understanding of adaptive responses to a changing world.
Here, we leverage the mechanisms of evolutionary response that we have discussed to suggest a baseline of testable hypotheses for how the facilitative role of plasticity may change as environmental parameters change (Box 1; Figure 2). Our primary goal is to call attention to how plasticity’s contribution to adaptive evolution depends on environmental context. Contradictory hypotheses abound; we contend that these in fact present focal targets for future empirical validation.
Box 1: Hypotheses for the Benefit of Plasticity on Adaptive Evolution in Response to Environmental Change
Current empirical and theoretical work allows us to define null hypotheses of how plasticity can impact adaptive evolution in response to changes in environmental mean rate of change, variation and autocorrelation. Each of these hypotheses utilizes moving optimum theory to infer how the relationship between phenotypic lag and adaptive tracking can be moderated by phenotypic plasticity. This interaction can result in a positive, negative or unimodal relationship between the environmental property and the benefit posed by plasticity for adaptive evolution.