title: Toxic cardenolides: chemical ecology and coevolution of specialized plant-herbivore interactions.
abstract: Cardenolides are remarkable steroidal toxins that have become model systems, critical in the development of theories for chemical ecology and coevolution. Because cardenolides inhibit the ubiquitous and essential animal enzyme Na⁺/K⁺-ATPase, most insects that feed on cardenolide-containing plants are highly specialized. With a huge diversity of chemical forms, these secondary metabolites are sporadically distributed across 12 botanical families, but dominate the Apocynaceae where they are found in > 30 genera. Studies over the past decade have demonstrated patterns in the distribution of cardenolides among plant organs, including all tissue types, and across broad geographic gradients within and across species. Cardenolide production has a genetic basis and is subject to natural selection by herbivores. In addition, there is strong evidence for phenotypic plasticity, with the biotic and abiotic environment predictably impacting cardenolide production. Mounting evidence indicates a high degree of specificity in herbivore-induced cardenolides in Asclepias. While herbivores of cardenolide-containing plants often sequester the toxins, are aposematic, and possess several physiological adaptations (including target site insensitivity), there is strong evidence that these specialists are nonetheless negatively impacted by cardenolides. While reviewing both the mechanisms and evolutionary ecology of cardenolide-mediated interactions, we advance novel hypotheses and suggest directions for future work.
authors.affiliation: Department of Ecology and Evolutionary Biology, and Department of Entomology, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Anurag A
authors.initials: AA
authors.lastname: Agrawal
authors.affiliation: Biozentrum Grindel, Molekulare Evolutionsbiologie, Martin-Luther-King Platz 3, 20146 Hamburg, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Petschenka
authors.affiliation: Department of Natural and Environmental Sciences, Western State College of Colorado, Gunnison, CO 81231, USA.
authors.forename: Robin A
authors.initials: RA
authors.lastname: Bingham
authors.affiliation: Department of Ecology and Evolutionary Biology, and Department of Entomology, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Marjorie G
authors.initials: MG
authors.lastname: Weber
authors.affiliation: Department of Ecology and Evolution, Bâtiment Biophore, University of Lausanne, CH - 1015 Lausanne, Switzerland.
authors.forename: Sergio
authors.initials: S
authors.lastname: Rasmann
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002298:Cardenolides / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D055669:Ecological and Environmental Phenomena; D060434:Herbivory / Q000187:drug effects* / Q000502:physiology*; D010802:Phylogeny; D010944:Plants / Q000187:drug effects*
chemical_list: D002298:Cardenolides