Warming alters sex-specific responses in leaf defense against insect herbivory in Populus cathayana

Abstract

Abstract Climate warming has been found to increase forest insect herbivory with potentially important consequences for the performance and distribution of plant species. Dioecious species often show sex-specific responses to abiotic drivers leading to spatial segregation of the sexes. However, little is known about sexual differences in defense against herbivorous insects in response to warming. We used a field survey and glasshouse experiment to test how sex-specific defenses of Populus cathayana against insect herbivory respond to warming. Consumed leaf area in females was greater than in males at +4 ℃ experimental warming or lower altitude. The warming treatment did not strongly affect differences in constitutive levels of leaf salicortin, condensed tannins (CT), salicylic acid (SA) and jasmonic acid (JA) between the two sexes. However, warming decreased herbivore-induced responses in salicortin, CT, SA, JA and defensive-related enzyme activities (e.g., superoxide dismutase, peroxidase, polyphenol oxidase and lipoxygenase) more in females than in males. Moreover, consumed leaf area in females showed more negative relationships with feeding-induced chemical defense traits than in males. These results show that sex-specific leaf defense against insect herbivory can be mediated by climate warming, and that higher leaf herbivory in females under warming is mainly influenced by decreases in induced defense responses rather than constitutive defense responses.