Abstract
Phenotypic plasticity is thought to impact evolutionary trajectories by shifting trait values in a direction that is either favored by natural selection (“adaptive plasticity”) or disfavored (“nonadaptive” plasticity). However, it is unclear how commonly each of these types of plasticity occurs in natural populations. To answer this question, we measured glucosinolate defensive chemistry and reproductive fitness in over 1,500 individuals of the wild perennial mustard Boechera stricta, planted in four common gardens across central Idaho, USA. Glucosinolate profiles—including total glucosinolate quantity as well as the relative abundances and overall diversity of different compounds—were strongly plastic both among gardens and along environmental gradients within gardens. The magnitude and direction of glucosinolate plasticity varied greatly among genotypes. We observed five cases of adaptive plasticity between gardens, in which glucosinolate profiles shifted in a direction that matched the direction of natural selection. In contrast, we found no evidence for nonadaptive glucosinolate plasticity between habitats. Evidence for within-habitat selection on glucosinolate reaction norm slopes (i.e., plasticity along a continuous environmental gradient) was inconclusive. Together, our results indicate that glucosinolate plasticity may improve the ability of B. stricta populations to persist after migration to new habitats.