Exposure of unwounded plants to chemical cues associated with herbivores leads to exposure-dependent changes in subsequent herbivore attack.

John L Orrock,Gustavo Bonaventure

doi:10.1371/journal.pone.0079900

Abstract

Although chemical predator cues often lead to changes in the anti-predator behavior of animal prey, it is not clear whether non-volatile herbivore kairomones (i.e. incidental chemical cues produced by herbivore movement or metabolism but not produced by an attack) trigger the induction of defense in plants prior to attack. I found that unwounded plants (Brassica nigra) that were regularly exposed to kairomones from snails (mucus and feces produced during movement of Helix aspersa) subsequently experienced reduced rates of attack by snails, unlike unwounded plants that received only one initial early exposure to snail kairomones. A follow-up experiment found that mucus alone did not affect snail feeding on previously harvested B. oleracea leaves, suggesting that changes in herbivory on B. nigra were due to changes in plant quality. The finding that chemicals associated with herbivores leads to changes in palatability of unwounded plants suggests that plants eavesdrop on components of non-volatile kairomones of their snail herbivores. Moreover, this work shows that the nature of plant exposure matters, supporting the conclusion that plants that have not been attacked or wounded nonetheless tailor their use of defenses based on incidental chemical information associated with herbivores and the timing with which cues of potential attack are encountered.

Highlights

Animals often use information from their environment to gauge the risk of attack by predators [1,2,3]
In the follow-up experiment, the presence of mucus alone was not a deterrent to snail feeding on B. oleracea; these results are expected to be conservative, since the mucus cues that would have been available to foraging snails in B. nigra herbivory trials would have represented a more dilute source of mucus and an older mucus cue
Differences in rates of herbivory were not driven by snail preference for plants of a particular size or because snails avoided mucus cues per se, as there were no differences in the size or number of leaves among plants prior to herbivory trials, no differences in snail visitation to plants, and mucus itself did not deter snail feeding in choice trials with B. oleoracea

Summary

Introduction

Animals often use information from their environment to gauge the risk of attack by predators [1,2,3] This information may take the form of kairomones, chemical cues that are not directly associated with attack by a predator [1]. Just as animals may give greater weight to cues that are received more recently or more often [4,5], plants might be sensitive to the timing of cue detection and the amount of cue received, since the timing of kairomone cue presentation and the amount of cue received may be important indicators of the reliability of the information provided by the cue [14]

Methods

Results

Conclusion