Summary Induced plant defense is commonly hypothesized to be an adaptive response to environmental heterogeneity reflecting phenotypic costs and benefits. While various studies have explored the adaptability of induced trichomes in response to biotic factors, we have limited understanding of whether induced trichomes can be an adaptive defense strategy in the presence of novel anthropogenic environmental stressors, such as herbicide exposure. Using annual invasive weed velvetleaf ( Abutilon theophrasti ), we explore whether induced trichome production contributes to herbicide resistance and determine its impact on growth and fitness in the presence and absence of glyphosate (active ingredient in “Roundup”). We observed trichome traits (proportion of polymorphs and density) and found a significant tradeoff between constitutive and inducible strategies for total trichome density. We identified positive correlations between induced total trichome density and herbicide resistance as well as induced branched trichomes and herbicide resistance. Additionally, our selection analysis revealed positive linear selection acting upon induced increase of total trichome production and correlative selection favoring high induced trichome production and intermediate growth. Overall, our study indicates that induced trichome production may evolve as an adaptive defense strategy in agroecosystems and identifies significant constraints impacting the evolution of induced trichome defense.

Building a barrier: investigating the defensive role of induced trichome production in herbicide exposed plants