Variation in herbivore defense strategies among plant species differing in elevational distribution and the role of temperature in defense

Temperature influences the distribution and performance of both plants and insect herbivores. Consequently, plant-herbivore interactions are likely to vary across thermal gradients, which could affect the evolution of plant defense. Furthermore, temperature fluctuations may elicit immediate changes in defense. To study the evolutionary and ecological aspects of plant antiherbivore defense depending on temperature, we conducted a transplant experiment on a mountain slope involving 30 Brassicaceae species varying in elevational distribution. Additionally, we carried out a climate-chamber experiment on a subset of 12 species to assess the temperature dependence of constitutive and induced defenses. The transplant experiment revealed that species from higher elevations experienced less herbivory than those from lower elevations. The climate-chamber experiment demonstrated that high-elevation species mounted stronger induced defenses in physical properties of leaves and in phytochemical diversity. Plant responses to low temperature, compared to control temperature, were lower constitutive defense and increased defense induction limited to leaf toughness. By contrast, high temperature increased constitutive chemical defense and defense-induced leaf toughness. Results suggest higher herbivory resistance in high-elevation Brassicaceae species by the induced remodeling of chemical defense. Such defense indication may have been shaped by rare but hard-to-tolerate herbivory in the evolutionary past.