Geographic variation and temporal changes in plant-herbivore interaction: Case studies with Solidago altissima in native and introduced ranges

Plants are subjected to environmental gradients and may encounter various herbivores, leading to geographic variation in defensive traits. The present review highlights that biological invasions are remarkable natural experiments for studying geographic variation in plant-herbivore interaction and tracking temporal dynamics in plant defense in response to environmental changes. Studies from this viewpoint can challenge various general topics in plant ecology, including the evolution of plant defense and indirect interactions among plants. First, I provide a brief overview on how the introduction of exotic herbivores drives rapid evolution after the establishment of exotic plants and its impacts on native plants. Second, I present a series of case studies investigating the patterns and mechanisms of geographic variation in the interaction between Solidago altissima and Corythucha marmorata (lace bug) in the native range in the United States and the introduced range in Japan. By combining biogeographical and experimental approaches, my collaborators and I unraveled the temporal dynamics of S. altissima's resistance to lace bugs and explored the drivers of differentiation in resistance between native and introduced ranges. These studies provide new insight into the geographic variation in exotic plant-herbivore interaction by unraveling the mechanisms and the temporal scale that cause the variation. These findings are vital not only for predicting invasiveness of exotic plants but also for understanding the evolution of plant-herbivore interaction in community contexts and under climate change.