Abstract

Many organisms respond to alarm calls of neighbors to change their behavior and morphology and thereby reduce their risk of consumption. The effectiveness of responses to alarm calls in animals can be enhanced by learning, and animals increase their responses to individuals known to provide more reliable or pertinent information. Sagebrush becomes more resistant to chewing herbivores after exposure to the volatiles of experimentally clipped conspecifics. This induced resistance has been shown to be more effective if the volatile cues come from individuals of the same chemotype as the receiver. It is not known if long term exposure to the cues of other chemotypes enhances the effectiveness of eavesdropping on different volatile cues. We conducted an experiment testing the effectiveness of damage-induced volatiles in a meadow of sagebrush dominated by individuals of two chemotypes -- thujone and camphor. As in previous experiments, branches exposed to damage-induced volatiles received less chewing damage over the growing season compared to control branches which did not receive volatiles. Plants of the camphor chemotype received less damage than those of the thujone chemotype. However, regardless of one's chemotype, when the damage-induced volatile cues and the long-term cues from neighbors matched, the induced defense became significantly stronger. These results raise the possibility that plants may learn to respond to different cues.