Leaves damaged by insect herbivory have consistently different biomechanical traits compared to undamaged leaves within individual plants

Leaf herbivory by insects is a widespread phenomenon across ecosystems, significantly impacting plant growth, survival, and community structure and biodiversity maintenance. While past research has mainly focused on interspecific and intraspecific differences in insect herbivory and its correlation with leaf traits, intra-individual variation in the susceptibility of leaves to insect herbivory remains under-investigated. Here, we investigated 5583 leaves from 584 seedlings of 40 woody species from a subtropical forest in southwestern China, focusing on five key leaf traits: size, specific leaf area (SLA), water content, thickness, and toughness. Our results revealed significant differences in these trait properties between insect-damaged and undamaged leaves from the same individual plant, with damaged leaves being larger, thicker, and harder, but having lower SLA and water content. These patterns were consistent across species, suggesting a conserved mechanism influencing the evolution of traits resisting insect herbivory. Furthermore, our findings offer valuable insights for future research on herbivory, particularly in terms of experimental design. Relying solely on traits from intact leaves may compromise the reliability of the leaf trait effects on herbivory. Traits of damaged leaves should also be considered to ensure the robustness of herbivory research.