Plasticity-led evolution: A survey of developmental mechanisms and empirical tests

Recent years have witnessed increased interest in evaluating whether phenotypic plasticity can precede, facilitate, and possibly even bias adaptive evolution. Despite accumulating evidence for "plasticity-led evolution" (i.e., "PLE"), critical gaps remain, such as: how different developmental mechanisms influence PLE; whether some types of traits and taxa are especially prone to experience PLE; and what studies are needed to drive the field forward. Here, we begin to address these shortcomings by first speculating about how various features of development-modularity, flexible regulation, and exploratory mechanisms-might impact and/or bias whether and how PLE unfolds. We then review and categorize the traits and taxa used to investigate PLE. We do so both to identify systems that may be well-suited for studying developmental mechanisms in a PLE context and to highlight any mismatches between PLE theory and existing empirical tests of this theory. We conclude by providing additional suggestions for future research. Our overarching goal is to stimulate additional work on PLE and thereby evaluate plasticity's role in evolution.