Pennsylvania State University University Park, Pennsylvania
Plants can use environmental cues to anticipate future attacks and ready their defenses. While early warnings are well studied in resisting (i.e., reducing) herbivory, how these cues affect tolerance of herbivore damage is less well known. We examined how environmental cues preceding herbivory influence tolerance and resistance in tall goldenrod Solidago altissima. When S. altissima is exposed to the putative pheromone of its specialist herbivore, the goldenrod gall fly Eurosta solidaginis, the plant primes the jasmonic acid (JA) defense pathway, resulting in greater resistance against the gall fly and other co-occurring herbivore species. Cue levels correlate with JA induction, but how JA levels affect fly survival and plant fitness was unknown. We exposed plants to varying concentrations of the priming cue under the contexts of multiple plant genotypes and herbivore populations and recorded gall induction and plant fitness. Plant genotype, fly population, and priming cue strength all influenced the rate of galling. Plants exposed to low doses of the priming cue were more resistant to galling than plants exposed to high doses, suggesting a non-linear relationship between cue exposure and defense. All plants exposed to the priming cue increased tolerance by producing more flowers than unexposed plants when plants were galled. In S. altissima, exposure to the priming cue appears to safeguard fitness by allowing plants to maintain flower production despite galling and perhaps by reducing gall formation, with the latter mediated cue intensity.
