Jasmonate and salicylate-mediated induced plant responses influence arthropod community assembly across seasons

Induced plant defenses regulated by the phytohormones jasmonic acid and salicylic acid are predicted to shape arthropod communities. While there is ample evidence that induced plant responses affect individual performance of herbivores, relatively little is known about their community-wide effects and the costs associated with induced defenses. We investigated the long-term effects of plant defenses on the arthropod community and plant fitness on the glandular trichome-bearing plant, Trichogoniopsis adenantha (Asteraceae), a native tropical plant, to assess the effects of jasmonate and salicylate defensive pathways on arthropod community structure. We used chemical elicitors to activate the jasmonate and salicylate defensive pathways on plants over 16 months. Our results showed that plant phytohormone induction altered host use by herbivores and beneficial arthropods. We found evidence for both induced resistance and susceptibility in response to different defensive pathways. Application of methyl jasmonate increased the concentration of pyrrolizidine alkaloids on leaves and flowers, and consequently reduced leaf herbivory and decreased seed damaged by pre-dispersal seed predators. In contrast, salicylate-induced plants were more susceptible to chewing herbivores and more resistant to sap-sucking herbivores. Induced plant responses did not affect the overall abundance of predators, however, we revealed contrasting species-specific responses. Although induced plants showed lower ovary damage, they suffered stronger fitness costs (i.e. reduced ovary fertilization) compared to controls. Our findings reveal the community-wide impacts of induced plant responses and underscore the importance of evaluating fitness costs associated with defenses. This study contributes to a broader understanding of ecological community organization in complex tropical systems.