Population differentiation related to climate of origin affects the intensity of plant–herbivore interactions in a clonal grass

Abstract

With ongoing climate change, it is likely that shifts in species distribution ranges will lead to changes in the type and intensity of plant–herbivore interactions. Plants currently exposed to lower levels of herbivory could have less developed defensive mechanisms and therefore could suffer in case of increased herbivore pressure.We performed a common garden experiment using clones of Festuca rubra originating from four populations experiencing contrasting temperature and precipitation regimes. Clones of identical genotype were subjected to both the control and the herbivory treatment using larvae of the nymphalid butterfly Coenonympha pamphilus, a generalist herbivore feeding on several grass species. Various measures of constitutive and induced defence as well as growth response to herbivory were assessed, compared between populations of different climatic origin and related to herbivore performance (larval survival).The four F. rubra populations significantly differed in constitutive defence (content of Si and total phenols), nutritional quality (content of C) and inducibility of defence (change in total phenols), but not in growth response to herbivory. Herbivores survived better on populations from colder climate and better survival was generally related to lower Si content and lower initial plant size.We demonstrated population differentiation in both constitutive and induced defence against insect herbivory, which directly affected survival of a generalist herbivore. Our findings confirmed the expectation that plants from higher elevations are more prone to herbivory. Moreover, differences in various aspects of plant defence between populations from the same altitude stresses the need of considering multiple factors when assessing the effect of climate on plant–herbivore interactions.