Clinal adaptation and phenotypic plasticity in Artemisia californica functional traits: Implications for arthropod community structure and plant adaptation to a changing environment

Steep climatic gradients may select for clinal adaptation in plant functional traits with implications for species interactions and response to future climate change. Although local adaptation and plasticity in plant functional traits have been documented for many species, less is known about population level variation in plasticity and whether such variation is driven by adaptation to environmental variation. Whether clinal adaptation in plants cascades up to influence arthropod community structure and patterns of diversity is virtually unknown. We examined clinal variation in Artemisia californica traits and performance - and plastic responses to environmental change - in a common garden of plants sourced from populations spanning a 700 km gradient characterized (from south to north) by a fourfold increase in precipitation and a 61% decrease in interannual precipitation variation. Plants cloned from five populations along this gradient were grown for 3 years in treatments of high and low precipitation. We collected whole arthropod communities from common garden plants to test whether geographic patterns of intraspecific variation in A. californica lead to parallel patterns of variation in arthropod community structure.;We found that genetically based physiological, herbivore defense, and phenological traits and plant performance in A. californica varied among source populations with most traits varying clinally in concordance with the steep latitudinal gradient in the abiotic environment and environmental variability. Overall, precipitation variability at population source sites was the best predictor of variation in plasticity among populations. Additionally, we found genetic variation in arthropod community structure, with density, evenness, and diversity increasing clinally with latitude. Overall, we show that patterns of intraspecific variation in arthropod communities correspond to patterns of variation in plant functional traits for this species. These striking, clinal patterns in plant traits and plasticity are indicative of adaptation to both the mean and variability of environmental conditions. Such clinal adaptation in plants is likely a primary factor influencing arthropod community structure and diversity at the landscape level. Our findings demonstrate that contemporary patterns of adaptation to environmental clines will mediate future plant responses to projected climate change, with implications for the maintenance of biodiversity at higher trophic levels.