title: A new method for measuring relative growth rate can uncover the costs of defensive compounds in Arabidopsis thaliana.
abstract: *Most plants suffer some degree of herbivore attack and many actively defend themselves against such an event. However, while such defence is generally assumed to be costly, it has sometimes proved difficult to demonstrate the costs of defensive compounds. *Here, we present a method for analysing growth rates which allows the effects of variation in initial plant size to be properly accounted for and apply it to 30 lines from a recombinant inbred population of Arabidopsis thaliana. We then relate different measures of relative growth rate (RGR) to damage caused by a specialist lepidopteran insect and to levels of putative defensive compounds measured on the same lines. *We show that seed size variation within the recombinant inbred population is large enough to generate differences in RGR, even when no other physiological differences exist. However, once size-standardized, RGR was positively correlated with herbivore damage (fast-growing lines suffered more damage) and was negatively correlated with the concentration of several glucosinolate compounds. *We conclude that defensive compounds do have a growth cost and that the production of such compounds results in reduced herbivore damage. However, size standardization of RGR was essential to uncovering the growth costs of defensive compounds.
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, Winterthurerstrasse 190, University of Zurich, Zurich CH-8057, Switzerland.
authors.forename: Cloé
authors.initials: C
authors.lastname: Paul-Victor
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, Winterthurerstrasse 190, University of Zurich, Zurich CH-8057, Switzerland.
authors.forename: Tobias
authors.initials: T
authors.lastname: Züst
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Rees
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Kliebenstein
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, Winterthurerstrasse 190, University of Zurich, Zurich CH-8057, Switzerland.
authors.forename: Lindsay A
authors.initials: LA
authors.lastname: Turnbull
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000737:chemistry* / Q000254:growth & development*; D005961:Glucosinolates / Q000032:analysis*; D007915:Lepidoptera; D008954:Models, Biological; D010935:Plant Diseases; D012639:Seeds / Q000033:anatomy & histology*
chemical_list: D005961:Glucosinolates