COSTS OF RESISTANCE TO NATURAL ENEMIES IN-FIELD POPULATIONS OF THE ANNUAL PLANT ARABIDOPSIS-THALIANA

The annual plant Arabidopsis thaliana is widely used as a model system in molecular genetics, but little is known about populations in the f ield. In this experimental field study of natural populations of Arabi dopsis, I tested the assumption that plant resistance has fitness cost s. Models of the evolution of resistance assume a cost, which is envis ioned as a reduction in fitness in the absence of natural enemies, suc h as insect herbivores and pathogens. The presumed basis of this cost is the diversion of limiting resources away from present and future gr owth and reproduction. Recent failures to detect allocation costs Of r esistance to herbivores have raised questions about whether costs exis t and, thus, about the appropriateness of theories that postulate such costs. I found genetic variation for two traits commonly thought to f unction as resistance characters: trichome density and total glucosino late concentration. Under field conditions, these characters both redu ced damage by the natural assemblage of herbivores and exhibited signi ficant fitness costs.