A Chemical Polymorphism in a Multitrophic Setting: Thyme Monoterpene Composition and Food Web Structure

• Published in: The American naturalist 2005-10, Vol.166 (4), p.517-529
• Main Authors: Linhart, Yan B., Keefover‐Ring, Ken, Mooney, Kailen A., Breland, Bianca, Thompson, John D.
• Format: Article
• Language: English
• Subjects: Animal Feed; Animals; Aphids - physiology; Aphis; Bromus; Bromus madritensis; Ecological competition; Ecological genetics; Ecology; Effects; Evolutionary biology; Food; Food Supply; Genetic Variation; Genotype & phenotype; Herbivores; Herbs; Mediterranean Region; Monoterpenes - analysis; Plant biochemistry; Plant Physiological Phenomena; Plants; Poaceae - physiology; Polymorphism; Polymorphism, Genetic; Predators; Smell; Species; Synecology; Taste; Thyme; Thymus Plant - chemistry; Thymus Plant - genetics; Thymus Plant - parasitology; Thymus vulgaris
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/444438

We investigated the effects of chemical variation in thyme (Thymus vulgarisL.) on its interactions with competitors, herbivores, and herbivore predators. Four different thyme monoterpene phenotypes (chemotypes) were grown in a \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $4\times 2\times 2$ \end{document} factorial of chemotype, caging (sham half‐cages vs. full cages), and competition (control vs. the grassBromus madritensisL.). Cages reduced numbers of arthropod predators. Thyme‐feeding aphidsAphis serpylliKoch passed through full cage walls to increase more than fourfold. As a result, freed from their predators, aphids had a large negative effect on thyme size and flowering. Similarly, competition fromBromushad a negative effect on thyme size and flowering. Individual effects of aphids and competition were nonadditive, however, and their combined effect was significantly less than that predicted by a multiplicative null model. Differential thyme sizes among chemotypes were not mediated by herbivores or competitors, but differential flowering was due to the effects of chemotype on aphids. We thus document differential selection by aphids among thyme chemotypes and the influence ofBromuson the strength of these negative effects of aphids.