title: Relaxation of herbivore-mediated selection drives the evolution of genetic covariances between plant competitive and defense traits.
abstract: Insect herbivores are important mediators of selection on traits that impact plant defense against herbivory and competitive ability. Although recent experiments demonstrate a central role for herbivory in driving rapid evolution of defense and competition-mediating traits, whether and how herbivory shapes heritable variation in these traits remains poorly understood. Here, we evaluate the structure and evolutionary stability of the G matrix for plant metabolites that are involved in defense and allelopathy in the tall goldenrod, Solidago altissima. We show that G has evolutionarily diverged between experimentally replicated populations that evolved in the presence versus the absence of ambient herbivory, providing direct evidence for the evolution of G by natural selection. Specifically, evolution in an herbivore-free habitat altered the orientation of G, revealing a negative genetic covariation between defense- and competition-related metabolites that is typically masked in herbivore-exposed populations. Our results may be explained by predictions of classical quantitative genetic theory, as well as the theory of acquisition-allocation trade-offs. The study provides compelling evidence that herbivory drives the evolution of plant genetic architecture.
authors.affiliation: School of Biological Sciences, Monash University, Victoria, 3800, Australia.
authors.forename: Akane
authors.initials: A
authors.lastname: Uesugi
authors.affiliation: School of Biological Sciences, Monash University, Victoria, 3800, Australia.
authors.forename: Tim
authors.initials: T
authors.lastname: Connallon
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14850.
authors.forename: André
authors.initials: A
authors.lastname: Kessler
authors.affiliation: School of Biological Sciences, Monash University, Victoria, 3800, Australia.|Centre for Geometric Biology, School of Biological Sciences, Monash University, Victoria, 3800, Australia.
authors.forename: Keyne
authors.initials: K
authors.lastname: Monro
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D060434:Herbivory; D007313:Insecta; D010641:Phenotype; D064209:Phytochemicals; D012641:Selection, Genetic; D036624:Solidago
chemical_list: D064209:Phytochemicals
keywords: Allelopathy; G-matrix; acquisition-allocation theory; plant secondary metabolites; plant-herbivore interaction; trade-off