COS 100-2 - CANCELLED - Constitutive and induced plant defense correlations along a productivity gradient

Abstract: Environmental gradients and associated changes in herbivore pressure can drive the evolution of plant defensive strategies, for example allocation to constitutive vs induced defenses. Long-standing plant defense theory predicts that among species, constitutive defenses against herbivores should be greater in low productivity regions (LPR) whereas inducible defenses should be greater in high productivity regions (HPR). While there is some empirical support for this pattern among species distributed across productivity gradients, it is unclear if the same patterns hold for single species. To address this knowledge gap, we measured constitutive and inducible defenses in populations of horsenettle (Solanum carolinense, Solanaceae) sampled across a latitudinal gradient of environment productivity. We obtained clones from genotypes from 18 populations along a 15° latitudinal gradient in eastern USA (1 genotype per population). We split each clone into two or three individuals and randomly allocated each individual to one of three treatments: i) JA treatment – plants were sprayed with jasmonic acid (JA), a plant hormone involved in defense induction, ii) insecticide – plants were sprayed with insecticide to avoid insect herbivore damage, iii) control - plants were sprayed with water. Plants from all treatments were placed separately in a common garden at the University of Florida, Gainesville, FL, where JA, insecticide and water were applied. We collected the first new leaves after the application of treatments to analyze different defensive traits. We found a trade-off between constitutive and induced defenses. Constitutive defenses were greater in plants from HPR, while induced defenses were greater in plants from LPR, opposite to predicted by theory. Overall, our results support growing evidence of trade-offs between plant defensive strategies (i.e., constitutive and induced defenses) with higher constitutive defenses in HPRs.