Costs and Benefits of Anti-Herbivore Defenses in Aspen

植物对草食的防御包括两个主要特征：抗性和耐受性。植物防御理论的一个基本前提是这些特征是昂贵的，因此在植物群体中存在显著的防御特征遗传变异。然而，证明假定的防御成本是非常困难的。支持成本概念的证据是模棱两可的，而且在木本植物物种方面几乎没有证据。在过去的15年里，对颤杨的研究揭示了(1)对爆发昆虫的易感性存在显著差异；(2)酚苷水平的基因型差异同样显著；(3)酚苷降低了以颤杨为食的昆虫的性能；(4)生长和酚苷浓度在颤杨基因型中存在强烈的环境依赖性权衡；(5)耐受性基因型差异的初步证据。本研究的目的是进一步探讨白杨与昆虫相互作用的进化生态学中防御的成本和收益。目的之一是确定白杨的抗性性状是否在实验和自然环境中提供保护。杨树基因型持续的落叶水平预计与酚苷浓度呈反比关系。试验将在一个普通的花园中进行，使用无性繁殖的白杨树生长在营养贫乏和营养丰富的土壤中。添加林帐毛虫会影响落叶。第二个目标是评估抗性和耐受性作为对食草性的防御性适应的独立和相互作用。预计白杨基因型会表现出抗性和耐受性的代价，并在抗性和耐受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，无性繁殖的树木生长在营养贫乏和营养丰富的土壤中。这一工作将有助于进一步了解植物防御食草动物的进化和生态学，以及防御系统进化的制约因素。这是第一次对木本植物的化学防御和耐化学性的成本和效益进行深入、同步的评估。而且，它涉及到在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.