Does competition magnify the fitness costs of induced responses in Arabidopsis thaliana? A manipulative approach

Abstract

Studies have increasingly shown that the constitutive or induced expression of resistance in plants is costly to fitness in the absence of enemy attack. If such costs are based on resource allocation tradeoffs, it has been hypothesized that resource limitation associated with plant competition increases the fitness costs of resistance. In two greenhouse studies, I examined the expression and costs of induced responses in pot-grown Arabidopsis thaliana grown alone or surrounded by six intraspecific neighbors. In the first study, I manipulated the expression of systemic acquired resistance (SAR) with the application of salicylic acid and monitored peroxidase activity and total seed production in treated plants. I used five lines of A. thaliana that varied in their competence to express SAR in this study. In the second study, I manipulated the expression of induced resistance (IR) with the application of jasmonic acid and monitored trypsin inhibitor activity and total seed production in treated plants. I used two lines of A. thaliana that varied in the competence to express IR in this study. Lines varied in their chemical and fitness responses to hormone treatment and competition in each study, but the application of wound-related hormones significantly increased levels of chemical defenses and reduced total seed production by an average of 15% overall in both studies. Competition reduced peroxidase activity by 6% in the first study, had no effect on trypsin inhibitor levels in the second study, and reduced total seed production by an average of 35% overall in both studies. However, there was no interaction between competition and hormone treatment on total seed production in either study. Induced responses were costly to fitness in A. thaliana, but competition had no effect on the magnitude of costs.

Costs and benefits of priming for defense in Arabidopsis

“…In wheat, Heil et al (6) demonstrated costs of SA-inducible defenses on growth and seed set. In Arabidopsis, Cipollini (7) showed that exogenously applied SA reduced seed production. Recently, Heidel et al (8) performed a field experiment with two sets of Arabidopsis genotypes: one group that is blocked in SA-inducible defenses and another group that constitutively expresses SA-inducible defenses.…”

Constitutive and inducible trypsin proteinase inhibitor production incurs large fitness costs in Nicotiana attenuata

“…This cost-benefit paradigm has motivated most of the theory about the evolution of plant defenses against herbivores (5)(6)(7)(8). Conclusive evidence attributing fitness costs to a particular defense trait has been elusive, but recent studies have made significant advances (9,10). The paradigm has been difficult to test for two reasons: (i) fitness costs, which can be measured as reductions in either male (11) or female (1,9,12) reproductive function, arise from many different types of compromises that could result from the expression of defense traits; and (ii) the fitness costs of a defense trait must be disentangled from the costs of genetically correlated traits (13)(14)(15).…”

“…2 and 3) have exploited inducible expression as a means of controlling for, or homogenizing, the genetic background of plants and have measured plant fitness before and after eliciting resistance in plants in herbivore-free environments. The discovery that herbivore attack elicits the JA cascade in many species, and that exogenous JA treatments elicits induced resistance without the wounding that normally accompanies herbivore attack, has motivated studies to measure the fitness costs of JA-induced responses (1,10,(26)(27)(28)(29). However, because of pleiotropic effects of the elicitors, the observed fitness differences do not arise solely from the expression of the resistant trait (12,30), and therefore these studies are likely to overestimate the fitness costs of resistance.…”

“…A recent exception to this trend is a study that used the jar1-1 mutant in Arabidopsis thaliana, which is deficient in JA signaling and expression of proteinase inhibitors (PIs), but surprisingly found greater reductions in seed production after JA elicitation in the mutant line than in the Col WT lines (10). Transformation technology provides a novel approach to manipulating plant resistance traits.…”

Exotic Plant Invasion in the Context of Plant Defense against Herbivores

“…Trade-offs between defense and growth and/or reproduction has been shown for quantitative defense traits such as protease inhibitors, which are considered costly chemicals to produce (Glawe et al, 2003;Zavala and Baldwin, 2006). Reallocation of resources from defense to growth may lead to better competitive ability (Cipollini and Bergelson, 2001;Cipollini, 2002;Moreno et al, 2009). Feng et al (2009 reported that the increased vigor of Ageratina adenophora, a neotropical invasive weed in Asia, is due to reallocation of nitrogen from cell walls (defense) to photosynthesis (growth), evidence that supports EICA.…”