Abstract

Functional traits are increasingly recognized as fundamental determinants for mediating ecological resilience. As global change accelerates, phenotypic plasticity in functional traits may provide a modality for fine-tuning responses to atypical or stressful environments. While various studies have explored induced plant trichomes as a response to biotic stress, emerging evidence suggests that trichome induction may also function as a broader tactic for managing a range of environmental stressors, including abiotic chemical stress. Using the annual invasive weed velvetleaf (Abutilon theophrasti), we examine whether herbicide exposure induces changes in trichome traits and whether these responses are associated with herbicide resistance and fitness outcomes. We quantified changes in trichome density and trichome type proportions across control and glyphosate (active ingredient in "Roundup") treated plants. We identified positive correlations between induced total trichome density and herbicide resistance, as well as induced branched trichomes and herbicide resistance. Selection analysis further revealed positive linear selection acting upon induced trichome density in the presence of herbicide, as well as correlative selection favoring induced trichome density and intermediate plant growth. Overall, our study indicates that plastic defenses like trichomes may contribute to plant performance under novel abiotic stress and highlights key constraints shaping the evolution of stress-responsiveness.