TRADE-OFFS AND ONTOGENETIC CHANGES IN RESISTANCE AND TOLERANCE TO INSECT HERBIVORY IN ARABIDOPSIS

Premise of research. As plants grow and develop larger roots and leaves, their access to resources increases. Consequently, reproductive plants should he able to invest in defense against herbivores more than younger plants. However, because plant defense may occur through resistance (traits that reduce herbivore damage) or tolerance (traits that reduce the negative effects of damage on plant fitness), ontogenetic changes in the pattern of resource allocation to growth, defense, and reproduction are likely to influence the relative investment in resistance and tolerance. Currently, many mechanisms of resistance are known, while mechanisms of tolerance are still rather unexplored, We investigated whether resistance and tolerance increase with ontogeny, whether tolerance is costly (i.e., lower seed production in the absence of damage), whether the relative investment into these two modes of defense changes with ontogeny, and whether plant growth rate and certain biomass allocation patterns are associated with tolerance. Methodology. In a greenhouse experiment, we measured resistance and tolerance to the generalist herbivore Trichoplusia ni in seven accessions of Arabidopsis thaliana at three ontogenetic stages: early vegetative (four-leaf rosette), first flower, and first fruit. Pivotal results, Both resistance and tolerance to T. ni larae increased from the vegetative stage to flowering and remained high through fruiting in A. thaliana. We found a negative association between resistance and tolerance that was very pronounced at the vegetative stage, decreased during flowering, and disappeared by the fruiting stage. We also found a cost of tolerance at the vegetative stage but not in later stages. Growth rate did not influence tolerance, but plants with greater root : shoot ratios were more tolerant of herbivory. Conclusions. Our study demonstrated that both resistance and tolerance increase with ontogeny and that the cost of tolerance and a pronounced trade-off between resistance and tolerance faded through ontogeny.