Document: RIC-3-23-6

Testing the moving target model of plant resistance.

KARBAN, R.* ¹, J.S.THALER ² and A.A.AGRAWAL ²

University of California, Davis, CA 95616 USA ¹
University of Toronto, Toronto, Ontario M5S3B2 CANADA ²

Abstract:
Induced resistance may involve either a consistent, directional change in the mean level of resistance or an increase in variance in resistance with no necessary change in the mean. An increase in variance of traits that provide resistance makes plants seem like moving targets to their herbivores; plants change after attack but not in a predictable manner. Although such a moving target strategy has been hypothesized to provide effective defense, few experiments have considered whether plants in fact become more variable following damage. This property can be tested easily by comparing the variance in resistance associated with damage to the variance associated with no damage. We illustrate this simple test with our own data and find that resistance in cucumber plants becomes more variable following feeding by spider mites. Other similar examples from the published literature are also presented. Increased variance may protect plants by making it difficult for herbivores to induce appropriate metabolic enzymes to match their food, by reducing herbivore benefits for a given mean level of nutrition, and by making it less likely that herbivores will evolve to circumvent plant defenses over evolutionary time.

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This abstract is being presented at: 3:20 PM in session:
Symposium # 23: Why Variation is Not Just Noise: The Influence of Variability on Plant-Herbivore and Plant-Pathogen Interactions.