Ontogenetic shifts in the response of woody plant seedlings to herbivore cues

Plants typically alter their chemical or physical defenses in response to herbivore damage. Recent studies have shown that herbivore cues including slug locomotion mucus, may also induce these plant responses. These induced responses are well-known in herbaceous- and mature broadleaf species, but how responses to herbivore cues vary during seedling ontogeny is little studied. Slugs feeding causes extensive mortality to young seedlings but often avoid older seedlings. The present study was designed to examine how induced responses to herbivore cues, locomotion mucus of the dusky slug Arion subfuscus, change during seedling ontogeny in sugar maple Acer saccharum. More specifically, we explored whether (1) exposure to slug locomotion mucus induce changes in growth and defenses including plant secondary metabolites expression in different–aged seedlings; (2) induced responses differ among different–aged seedlings; and (3) exposure to herbivore cues increase resistance in seedlings to future herbivory. Three different-aged sugar maple seedlings (4, 7, and 10-week) grown in a greenhouse were treated with either distilled water, methyl jasmonate or slug locomotion mucus for 5 times (every 3^rd day). After termination of treatments, plants were destructively sampled after 4 and 14 days to assess changes in plant growth (height, number of leaves, plant biomass) and secondary metabolite concentration. Herbivory bioassays were performed by releasing a single slug into Petri dishes that contained a leaf disc of one of the treated plants. After 24 h, the slug was removed, and the leaf area consumed was measured. The results of this study will be presented and discussed.