Costs and Benefits of Anti-Herbivore Defenses in Aspen

植物对食草病的防御包括两个主要特征：抗性和耐性。植物防御理论的一个基本前提是，这些性状是昂贵的，因此在植物种群内存在显著的防御性状遗传变异。然而，事实证明，证明辩护的推定成本出人意料地困难。就木本植物物种而言，支持成本概念的证据是模棱两可的，而且微不足道。在过去的15年里，对颤栗杨树的研究揭示了(1)对暴发害虫的敏感度的显著差异，(2)酚苷水平的同样显著的基因型差异，(3)酚苷降低了杨树食性昆虫的性能，(4)杨树基因型间生长和酚苷浓度之间强烈的、环境相关的权衡，以及(5)耐受性的基因变异的初步证据。这项研究的目的是进一步研究杨树-昆虫相互作用进化生态学中防御的成本和收益。一个目标是确定杨树抗性性状是否在实验和自然环境中提供保护。据预测，杨树基因型所承受的落叶程度与酚苷浓度成反比。这项实验将在一个普通的花园中进行，使用的是生长在营养贫瘠和营养丰富的土壤中的无性系繁殖的杨树。落叶将通过增加森林帐篷毛虫来实现。第二个目标是评估抵抗和耐受作为对食草动物的防御性适应的独立和交互作用。据预测，杨树的基因型表现出抗性和耐性的代价，并在抗性和耐性之间表现出负的遗传权衡。这将在一个普通的花园中进行，无性系繁殖的树木生长在营养贫瘠和营养丰富的土壤中。这项工作具有重要意义，因为它将加深对植物防御草食动物的进化和生态学的理解，以及对限制防御系统进化的因素的理解。它构成了对木本植物中化学防御和耐受性的成本和收益的第一次深入的、同时的评估。而且，它涉及北美早期演替森林中具有广阔地理范围和关键生态重要性的物种。

0074427LindrothPlant defense against herbivory involves two principal traits: resistance and tolerance. A fundamental premise of plant defense theories is that such traits are costly, hence the existence of significant genetic variation in defense characteristics within plant populations. Demonstration of putative costs f defense however, has proved to be surprisingly difficult. Evidence supporting the notion of costs is equivocal and vanishingly small with respect to woody plant species. Over the last 15 years, research on quaking aspen has revealed (1) striking variation in susceptibility to outbreak insects, (2) equally striking genotypic variation in levels of phenolic glycosides, (3) phenolic glycosides reduce performance of aspen-feeding insects, (4) strong, environmentally-dependent trade-offs between growth and phenolic glycoside concentrations in aspen genotypes, and (5) preliminary evidence of genotypic variation in tolerance. The purpose of this research is to further investigate the costs and benefits of defense in the evolutionary ecology of aspen-insect interactions. One objective is to ascertain whether aspen resistance traits afford protection in experimental and natural settings. Levels of defoliation sustained by aspen genotypes are predicted to vary in inverse relation to phenolic glycoside concentrations. The experiment will be conducted in a common garden using clonally propagated aspen trees growing in nutrient-poor and nutrient-rich soil. Defoliation will be effected by addition of forest tent caterpillars. A second objective is to evaluate the independent and interactive roles of resistance and tolerance as defensive adaptations against herbivory. Aspen genotypes are predicted to exhibit costs of resistance and tolerance, and to exhibit negative genetic trade-offs between resistance and tolerance. This will be conducted in a common garden, with clonally propagated trees growing in nutrient-poor and nutrient-rich soils. This work is significant in that it will improve understanding of the evolution and ecology of plant defense against herbivores, and of factors constraining the evolution of defense systems. It constitutes the first in-depth, simultaneous evaluation of costs and benefits of chemical defense and tolerance in a woody plant. And, it involves species with expansive geographic ranges and pivotal ecological importance in early successional forests of North America.