Plants have evolved two major mechanisms in response to frequent attacks from insect herbivores. While resistance reduces the levels of damage suffered by plants, tolerance reduces the negative effects of herbivory on plant fitness. Despite their roles in defense and consequent fitness advantage, the evolution of these two characters may be constrained by the fitness costs associated with their production. In addition, these costs may be influenced by variation in environmental conditions. In a common garden experiment, the effects of ultraviolet B (UVB) radiation on plant resistance and tolerance to insect herbivory was evaluated by exposing recombinant inbred lines of Arabidopsis thaliana to natural levels of insect herbivory under two levels of UVB radiation (ambient and excluded UVB). Specifically, this study evaluated the existence of genetic variation in plant resistance and tolerance to insect herbivory under variable UVB radiation and whether changes in UVB radiation modify fitness costs associated with tolerance and resistance.
Results from this study revealed the presence of genetic variation in plant resistance and tolerance and that this variation is dependent on UVB radiation levels. In addition, there were differences in the fitness cost of plant resistance and tolerance across UVB environmental gradients. However, no trade-offs between resistance and tolerance was observed. These results highlight implications of changes in UVB radiation on future evolution of important plant characters involved in plant defense to insect herbivory.