Evol Ecol Res 1: 151-171 (1999)     Full PDF if your library subscribes.

Thyme is of the essence: Biochemical polymorphism and multi-species deterrence

Yan B. Linhart1 and John D. Thompson2

1Department of Environmental, Population and Organismic Biology, University of Colorado at Boulder, Campus Box 334,Boulder, CO 80309-0334, USA and 2Centre d’Ecologie Fonctionelle et Evolutive, CNRS, Route de Mende, BP 5051, F-34033 Montpellier Cedex, France

Author to whom all correspondence should be addressed.
e-mail: Yan.Linhart@colorado.edu


Populations of the common thyme (Thymus vulgaris, Labiatae) are characterized by a complex genetic and biochemical polymorphism. Individual plants manufacture a single dominant monoterpene which gives them a characteristic smell and taste, and the genetic determination of these chemotypes involves a series of five loci interacting with each other in epistatic fashion. We tested the hypothesis that multi-species herbivory and allelopathy are associated with this monoterpene polymorphism. We compared the relative attractiveness and deterrence of various chemotypes by offering either thyme plants or artificial diets laced with monoterpenes to six herbivores: two molluscs, two insects and two mammals. In addition, we summarize experiments by us and others in which bacteria, fungi and seeds of the grass Brachypodium phoenicoides, a common competitor of T. vulgaris, were exposed to the individual monoterpenes. The results show that the monoterpenes have differential deterrence value against these various species. We conclude that a combination of selective herbivory and allelopathy contributes to the maintenance of this polymorphism.

Keywords: genetic polymorphism, herbivory, Mediterranean ecosystems, monoterpene variation, Thymus vulgaris.

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