Ontogenetic changes in defence against a generalist herbivore in Arabidopsis thaliana

Plant defence against herbivores includes resistance (avoiding damage) and tolerance (reducing the negative fitness effects of damage). As plants grow and increase their resource-garnering capacity, they should invest more in defence, but tradeoffs between plant functions may also change with ontogeny, thus complicating predictions on the simultaneous ontogenetic trajectories of resistance and tolerance. In a laboratory experiment, we used ten accessions of Arabidopsis thaliana that represent a gamut of resistance levels naturally found in the species to examine whether resistance and tolerance increase between an early vegetative stage and the fruit-ripening stage, and to test for tradeoffs between both defence modes. We measured constitutive resistance and tolerance to larvae of the generalist moth, Trichoplusia ni, and estimated costs of tolerance at both ontogenetic stages. We found an increase in constitutive resistance from the vegetative to the fruit-ripening stage, but not for tolerance. Accessions differed in tolerance, but not in resistance. Despite finding significant costs of tolerance at both ontogenetic stages, we found no tradeoff between resistance and tolerance. An examination of biomass partitioning at senescence revealed that the plants with a propensity to make roots were more tolerant to herbivory. Our results show that the ontogenetic trajectories of resistance and tolerance can be different, and even though costs of tolerance may be detected, these are not necessarily linked to a tradeoff with resistance. Lastly, the capacity of plants to grow a large shoot (mostly inflorescence) and make root tissue is linked to their ability to tolerate herbivory.