PARENT SESSION
Oral Session #28: Plant-Animal Interactions. Presiding: S. Louda.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.

Costs of resistance and tolerance against herbivores in the context of plant-plant interactions.

Siemens, David¹, Roy, Bitty¹, ¹

ABSTRACT- Plants are often less defended in nature than one might expect if these traits were shaped by directional selection from herbivores. One explanation for these lower defense levels is that there are costs associated with genetic variation in defense production, which balances selection on defenses. However, direct tests of costs are often equivocal, suggesting that costs are not important, or that costs depend on some other ecological factor. A recent hypothesis states that costs may increase and become important when environments become more stressful. We tested whether costs of resistance and tolerance defenses increased when plants of western Arabis grew with a common neighbor Bouteloua gracilis. Species of Arabis are the closest wild relatives of Arabidopsis. Contrary to the hypothesis, costs of tolerance and resistance were detected when Arabis grew in isolation, but not in the competitive situation. Decreased costs of resistance in stressful environments is consistent with other theory on the evolution of secondary metabolism. However, a decrease in costs of tolerance is not easily explained in the context of current theory.

KEY WORDS: cost of defense, tolerance, resistance, Arabis