Journal of Chemical Ecology

, Volume 40, Issue 7, pp 717–729 | Cite as

Specificity of Herbivore-Induced Hormonal Signaling and Defensive Traits in Five Closely Related Milkweeds (Asclepias spp.)

  • Anurag A. Agrawal
  • Amy P. Hastings
  • Eamonn T. Patrick
  • Anna C. Knight


Despite the recognition that phytohormonal signaling mediates induced responses to herbivory, we still have little understanding of how such signaling varies among closely related species and may generate herbivore-specific induced responses. We studied closely related milkweeds (Asclepias) to link: 1) plant damage by two specialist chewing herbivores (milkweed leaf beetles Labidomera clivicolis and monarch caterpillars Danaus plexippus); 2) production of the phytohormones jasmonic acid (JA), salicylic acid (SA), and abscisic acid (ABA); 3) induction of defensive cardenolides and latex; and 4) impacts on Danaus caterpillars. We first show that A. syriaca exhibits induced resistance following monarch herbivory (i.e., reduced monarch growth on previously damaged plants), while the defensively dissimilar A. tuberosa does not. We next worked with a broader group of five Asclepias, including these two species, that are highly divergent in defensive traits yet from the same clade. Three of the five species showed herbivore-induced changes in cardenolides, while induced latex was found in four species. Among the phytohormones, JA and ABA showed specific responses (although they generally increased) to insect species and among the plant species. In contrast, SA responses were consistent among plant and herbivore species, showing a decline following herbivore attack. Jasmonic acid showed a positive quantitative relationship only with latex, and this was strongest in plants damaged by D. plexippus. Although phytohormones showed qualitative tradeoffs (i.e., treatments that enhanced JA reduced SA), the few significant individual plant-level correlations among hormones were positive, and these were strongest between JA and ABA in monarch damaged plants. We conclude that: 1) latex exudation is positively associated with endogenous JA levels, even among low-latex species; 2) correlations among milkweed hormones are generally positive, although herbivore damage induces a divergence (tradeoff) between JA and SA; 3) induction of cardenolides and latex are not necessarily physiologically linked; and 4) even very closely related species show highly divergent induction, with some species showing strong defenses, hormonally-mediated induction, and impacts on herbivores, while other milkweed species apparently use alternative strategies to cope with insect attack.


Cardenolides Coevolution Common milkweed Asclepias syriaca Jasmonic acid Latex Monarch butterfly Danaus plexippus Phytohormones Plant-insect interactions 



This study was improved by discussions and input from Jared Ali, Rayko Halitschke, Monica Kersch-Becker, Georg Petschenka, Jennifer Thaler, Tobias Züst, and the Phytophagy Lab at Cornell University. We thank Mark Fishbein for help with the phylogeny of Asclepias and Marc Johnson and Peter Van Zandt for collecting A. obovata seeds. We thank T. Ramsey for help conducting the experiments, E. Kearney and C. Creneti for sample preparation, and J. Kerr for help with cardenolide analysis. Our research and lab ( is currently supported by NSF-DEB 1118783 and the Templeton Foundation.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • Anurag A. Agrawal
    • 1
  • Amy P. Hastings
    • 1
  • Eamonn T. Patrick
    • 1
  • Anna C. Knight
    • 1
  1. 1.Department of Ecology and Evolutionary Biology, and Department of EntomologyCornell UniversityIthacaUSA

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