title: Exploring plant defense theory in tall goldenrod, Solidago altissima.
abstract: Understanding the evolutionary reasons for patterns of chemical defense in plants is an ongoing theoretical and empirical challenge. The goal is to develop a model that can reliably predict how defenses are distributed within the plant over space and time. This is difficult given that evolutionary, ecological, and physiological processes and tradeoffs can operate over different spatial and temporal scales. We evaluated the major predictions of two leading defense theories, the growth-differentiation balance hypothesis (GDBH) and optimal defense theory (ODT). To achieve this, enemies, fitness components, terpenoids, and protease inhibitors were measured in Solidago altissima and used to construct conventional univariate and structural equation models (SEMs). Leaf-tissue value indices extracted from an SEM revealed a strong correlation between tissue value and terpenoid defense that supports ODT. A tradeoff between serine protease inhibition and growth as well as an indirect tradeoff between growth and terpenoids manifested through galling insects supported the GDBH. Interestingly, there was a strong direct effect of terpenoids on rhizome mass, suggesting service to both storage and defense. The results support established theories but unknown genotypic traits explained much of the variation in defense, confirming the need to integrate emerging theories such as pollination constraints, defense syndromes, tolerance, mutualisms, and facilitation.
authors.affiliation: Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Heath
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, 445 Corson Hall, Ithaca, NY, 14853, USA.
authors.forename: André
authors.initials: A
authors.lastname: Kessler
authors.affiliation: Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Woebbe
authors.affiliation: Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA.
authors.forename: Don
authors.initials: D
authors.lastname: Cipollini
authors.affiliation: Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA.
authors.forename: John O
authors.initials: JO
authors.lastname: Stireman
mesh_terms: D000818:Animals; D018533:Biomass; D060434:Herbivory; D007313:Insecta / Q000502:physiology; D015233:Models, Statistical; D010641:Phenotype; D010935:Plant Diseases / Q000276:immunology*; D057865:Plant Immunity; D018515:Plant Leaves / Q000737:chemistry / Q000276:immunology / Q000502:physiology; D011480:Protease Inhibitors / Q000378:metabolism; D027343:Rhizome; D036624:Solidago / Q000737:chemistry / Q000276:immunology* / Q000502:physiology; D013729:Terpenes / Q000302:isolation & purification*
chemical_list: D011480:Protease Inhibitors; D013729:Terpenes
keywords: Solidago altissima; growth differentiation balance hypothesis; optimal defense; plant defense; resource allocation