Collaborative Research: Using herbivore kairomones to assess short-term and legacy risk responses in the early life stages of long-lived woody plants

Even though plants cannot move, they are far from defenseless against their herbivores. While research exploring how plants protect themselves has focused largely on changes in plant defense that occur in response to herbivore attack, it has recently been shown that plants can detect and respond to herbivore cues (referred to as ‘kairomones’) even before an attack begins.

Mucus from snails and slugs, herbivores that attack seeds and seedlings, triggers defensive responses in seedlings that help the plants survive subsequent attack by slugs or other herbivores. Such defenses may be particularly important for seedling sugar maple trees, an iconic tree in the northeastern US critical to the maple sugar industry that is declining throughout its range.

An invasive slug, the dusky Arion, poses a major threat to newly germinated sugar maple seedlings; this project addresses how mucus from this slug affects the anti-herbivore defenses of sugar maples ranging in age from seedlings to saplings. It also evaluates whether early-life exposure to mucus can help protect sugar maples against later-arriving herbivores ranging from gypsy moths to white-tailed deer.

The project also funds work by the Rhode Island-based Science and Math Investigative Learning (SMILE) program, a classroom-based organization that works with kids grades 4-12 to increase the numbers of educationally disadvantaged students who graduate from high school prepared to enter higher education and pursue STEM careers. Students work with project scientists on field- and classroom-based experiences that employ inquiry-based learning to reveal ecological principles and explore local ecosystems.

Despite substantial research exploring plant defense induction during and after herbivore attack, little is known about whether and how plants use pre-attack cues such as kairomones (herbivore-emitted chemicals not associated with attack that are detected by - and thus provide benefits to - a plant) to preemptively induce defense. Herbivore kairomones have recently been documented in multiple systems; slug/snail mucus, an easily obtained and manipulable kairomone, can be used to ask novel questions about plant risk perception and induced responses.

The fact that slugs preferentially attack seedlings, a highly vulnerable life history stage, highlights the selective advantage of pre-attack mucus detection and response. The following questions are addressed in a long-lived woody plant system: How do different risk cues affect growth and defense of different-aged seedlings?; How do ontogenetic shifts in susceptibility determine patterns of responses?; What are the immediate and legacy consequences of risk perception and ontogeny in the field?

These questions are asked using the slug Arion subfuscus and the sugar maple Acer saccharum in experiments exploring interactions between risk cue quality and seedling age over both short (~1 month) and long (>1 yr.) time periods. This is the first study of how kairomones affect woody plant defense, growth, and subsequent herbivore vulnerability. The manipulation of herbivore cues, ontogeny, and differential susceptibility within and across seasons explores whether current plant defense reflects the ‘ghost of herbivory risk past’; present-day defense may often only make sense considering past information received by plants.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.