Plants can evolve resistance traits to reduce herbivore damage and/or tolerance traits to minimize the negative fitness effects of herbivore damage. The selection and maintenance of resistance and/or tolerance may be influenced by aspects of the environment. A less explored area of research is how temporal changes in the environment may affect the selection of resistant and tolerant genotypes within populations of long-lived perennial plants. If environmental conditions influence the selection of locally adapted defense traits, then changes in environmental conditions during succession will alter defense expression. We surveyed Canada goldenrod (Solidago canadensis) defense traits within three early- and three late- successional fields and experimentally measured resistance, tolerance, and their associated costs and benefits for the same genotypes in a common garden to examine whether defense expression co-varies with respect to environmental conditions associated with different successional stages.
Results/Conclusions Early-successional fields had higher stem density of neighboring forbs and grasses and lower canopy cover than late-successional fields. Resistance was spatially correlated with neighboring stem density in early-successional fields and tolerance traits were spatially correlated with canopy cover in late-successional fields. In the common garden where no neighbors and no shade was present, genotypes planted from early-successional fields had lower resistance to herbivory, while for late successional genotypes, resistance was higher than in the original field. We found no cost to resistance but a significant cost to tolerance only in genotypes from the early-successional fields. Together, these studies suggest that S. canadensis defense expression may be influenced by the context of their environment and may shift from a resistance to tolerance strategy during old-field succession.