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.