Evolutionary dynamics of interactions between plants and their enemies: comparison of herbivorous insects and pathogens

Abstract Plants colonized land over 400 million years ago. Shortly thereafter, organisms began to consume terrestrial plant tissue as a nutritional resource. Most plant enemies are plant pathogens or herbivores, and they impose natural selection for plants to evolve defenses. These traits generate selection pressures on enemies. Coevolution between terrestrial plants and their enemies is an important element of the evolutionary history of both groups. However, coevolutionary studies of plant–pathogen interactions have tended to focus on different research topics than plant–herbivore interactions. Specifically, studies of plant–pathogen interactions often adopt a “gene‐for‐gene” conceptual framework. In contrast, studies of plants and herbivores often investigate escalation or elaboration of plant defense and herbivore adaptations to overcome it. The main exceptions to the general pattern are studies that focus on small, sessile herbivores that share many features with plant pathogens, studies that incorporate both herbivores and pathogens into a single investigation, and studies that test aspects of Thompson's geographic mosaic theory for coevolution. We discuss the implications of these findings for future research.