Herbivore risk alters plant palatability across woody plant ontogeny

While woody saplings and mature plants generally tolerate moderate herbivory, their seeds and young seedlings are much more vulnerable. Because damage from even a single herbivore can be fatal to early life stages, seeds and young seedlings should benefit from detecting pre-attack herbivore cues and using them to induce defense. The early life-stages of several plant species have been shown to induce defense in response to herbivore kairomones, non-attack-related substances such as feces or slime produced by consumers that are detected by and benefit their prey. Using a generalist herbivore (the slug Arion subfuscus) and tree (Acer saccharum) as a model system, we investigated whether prior exposure to Ar. subfuscus locomotion slime affects A) herbivory on variously aged Ac. saccharum seeds and seedlings; and B) the rate and speed of Ac. saccharum seed germination and seedling growth. Starting 20 days into cold stratification, we exposed Ac. saccharum seeds to either slime-treated dirt (treatment) or dirt alone (control). We then conducted paired-choice Ar. subfuscus bioassays at five ontogenetic stages (seeds, radicles, cotyledons, new first leaves, mature first leaves, and new second leaves) to assess herbivory at each stage and whether prior exposure to slug slime altered damage. Seed germination rate/speed and seedling biomass was recorded prior to each bioassay to assess whether risk cues altered germination and subsequent growth.