Effects of Leaf Herbivory on Floral Trait Correlations and Scent Composition in Asclepias syriaca.

Flowering plants attract pollinators via traits such as floral scent and morphology, which are often influenced by other interactions like herbivory. However, the effects of herbivory on floral traits may not be consistent across traits, resulting in changed relationships between multimodal traits that could alter pollinator perception. We investigated how herbivory affects floral scent and morphology, and alters correlations between signaling traits. In a natural community, we simulated herbivory seven days before flowering on eight Asclepias syriaca (common milkweed) plants by removing half of their foliar tissue and applying a jasmonic acid solution; eight additional plants received a control spray with solvent only and no damage. After treatments, we collected floral volatile organic compound (VOC) emissions (i.e., scent) and measured five floral morphological traits on all plants. We found that simulated herbivory significantly altered VOC composition. Additionally, herbivory increased flower diameter and hood width while decreasing hood height, but had no effect on inflorescence size, measured as flower number or dry mass. Notably, we found that simulated herbivory led to significantly stronger correlations in floral traits, including both flower morphology-VOC correlations and VOC-VOC correlations. This study demonstrates that herbivory induces changes in floral morphological traits and VOC emissions and increases correlations between floral traits. These findings highlight how herbivory can interfere with the floral traits that plants use to signal their pollination partners.