| Fitness costs are often assumed to result from allocations to defense but it is difficult to separate the fitness costs from other unknown factors. I use a genetic approach to induce defenses without otherwise affecting the organism. Using this approach I induce Systemic Acquired Resistance (SAR) in Arabidopsis thaliana to determine both the fitness costs and benefits of SAR. In both field and growth chamber studies SAR has a fitness cost that is slightly lowered when nutrients are limited. The result supports the theory that under limiting resources, plants will reduce allocation to defense thus reducing fitness costs. Reduced pathogen symptoms did not result in a fitness benefit for induction. Benefits may exist under different pathogen conditions but, the severe cost suggests that SAR is not constitutive because it is too costly. The induction did not have a significant effect on herbivory demonstrating that SAR does not impair herbivory defense, at least at the level of herbivory found in this experiment. |
