Evolution of phenotypic plasticity: genetic differentiation and additive genetic variation for induced defense in wild arugula Eruca sativa

Phenotypic plasticity is the primary mechanism of organismal resilience to
abiotic and biotic stress, and genetic differentiation in plasticity can
evolve if stresses differ among populations. Inducible defense is a common
form of adaptive phenotypic plasticity and long-standing theory predicts
that its evolution is shaped by costs of the defensive traits, costs of
plasticity, and a trade-off in allocation to constitutive versus induced
traits. We used a common-garden to study the evolution of defense in two
native populations of wild arugula Eruca sativa (Brassicaceae) from
contrasting desert and Mediterranean habitats that differ in attack by
caterpillars and aphids. We report genetic differentiation and additive
genetic variance for phenology, growth, and three defensive traits (toxic
glucosinolates, anti-nutritive protease inhibitors, and physical trichome
barriers) as well their inducibility in response to the plant hormone
jasmonic acid. The two populations were strongly differentiated for
plasticity in nearly all traits. There was little evidence for costs of
defense or plasticity, but constitutive and induced traits showed a
consistent additive genetic trade-off within each population for the three
defensive traits. We conclude that these populations have evolutionarily
diverged in inducible defense and retain ample potential for the future
evolution of phenotypic plasticity in defense.