Print PageChemical defenses in plants provide a rich array of responses to environmental stress, yet the expression of these defenses carries myriad ecological, genetic, and biochemical costs. Inducible defenses are thought to reduce the allocation costs associated with defense in addition to deterring specialist herbivores and providing variation in host resources, thereby increasing host resistance and slowing adaptation of herbivores. Yet, inducible defenses often exhibit a negative relationship with constitutive defenses in the presence of a generalist herbivore. This has led to the hypothesis that environments favoring specialist herbivores will favor the evolution of inducible defenses as well. We test this hypothesis by assaying levels of induction across a monophyletic clade of plants and pairing these data with biogeographical data (a proxy for specialist habitats).
Results/Conclusions
Tomato (Solanum lycopersicum) is well known for demonstrating induced defenses in response to attack or wounding. Among wild species we find tremendous variation for levels of induction and constitutive defense (p=0.0001). Additionally, we find that inducible defenses in this clade appear to be independent of historical contingencies as there are multiple species that exhibit intra-specific variation in induced defense response. Finally, we find a relationship between “specialization” and variation in induced defense response (Mantel test, p=0.027) supporting the hypothesis that in wild tomatoes environments favoring specialization also favor the evolution of induced defenses. Our work suggests that induced defenses may have evolved in response to specialist herbivores and was later co-opted to reduce allocation costs.
