DISSERTATION RESEARCH: Exploiting Seasonality and Differences in Herbivory to Create a Novel Framework for Testing Optimal Defense Theory

植物构成了大多数陆地食物网的基础，害虫消耗的植物组织比所有其他动物的总和还要多。因此，了解植物如何抵御虫害对于维持重要的生态系统服务和粮食生产至关重要。与老叶相比，幼叶通常对未来的植物成功更有价值，也更有营养，对昆虫也更有吸引力，但年轻的组织可能对这种攻击有更多的防御能力。植物的生长机制本身可能解释了这种模式，或者它可能是一种进化适应，以保护自己免受害虫侵害。一系列实验将使用过去400年来分别在低水平或高水平虫害下进化的植物种群，测试单独或具有防御反应的生长生理学的替代解释。这项工作将纳入本科生的贡献。这项研究将检验植物与昆虫相互作用研究的基石--最优防御理论，该理论预测，食草动物选择年轻组织比老组织受到更好的保护。然而，生理限制，而不是对食草动物强加的选择的适应性反应，可能会导致相同的模式。在这项提议中，我的目标是通过解开适应性进化或生理限制是否导致防御分配的差异来促进对幼叶如此高度防御的原因的理解。为了测试生理约束与适应性进化的交替假设，将开发一个严格的新的最佳防御框架，该框架要求防御测试：(1)包括根组织，(2)直接测量相对组织值，以及(3)评估这些值如何在生长季节变化。该框架将通过对特定组织的植物种群进行种内比较来测试，这些植物种群对特定组织的攻击风险(通过使用欧洲和北美的Verbascum thapsis母系)可以预测地有所不同，使用的方法是盆栽实验，并测量组织价值(组织移除和种子产量)和化学防御分配。

Plants form the basis of most terrestrial food webs, and insect pests consume more plant tissue than all other animals combined. Thus, understanding how plants defend against insect pests is crucial to maintaining important ecosystem services and food production. Compared to old leaves, young leaves are often more valuable to future plant success as well as more nutritious and desirable to insects, but younger tissue may have more defenses against such attack. The mechanisms of plant growth alone might explain this pattern, or it could be an evolutionary adaptation to protect against pests. A series of experiments will test the alternate explanations of growth physiology alone or with defense response using populations of plants that have evolved separately under either low or high levels of insect attack for the last 400 years. The work will incorporate the contributions of undergraduate students.This research will examine a cornerstone of research on plant-insect interactions, the optimal defense theory, which predicts that herbivory selects for young tissues to be better defended than old tissue. However, physiological constraints, as opposed to adaptive responses to selection imposed by herbivory, could lead to the same patterns. In this proposal, I aim to advance understanding of what drives young leaves to be so highly defended by disentangling whether adaptive evolution or physiological constraints drives differences in allocation in defense. To test the alternate hypotheses of physiological constraints versus adaptive evolution, a rigorous new framework of optimal defense will be developed that requires tests of defense to: (1) include root tissue, (2) directly measure relative tissue values, and (3) evaluate how these values change through a growing season. The framework will be tested using an intraspecific comparison between plant populations that predictably vary in their risk of attack (by using European and North American maternal lines of Verbascum thapsis) for specific tissues using pot experiments and measures of tissue value (tissue removal and seed output) and chemical defense allocations.