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，而害虫消耗的植物组织比所有其他动物消耗的总和还要多。因此，了解植物如何抵御害虫对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，嫩叶通常对植物未来的成功更有价值，也更有营养，更受昆虫的欢迎，但年轻的组织可能有更多的防御能力来抵御这种攻击。植物生长的机制可以单独解释这种模式，或者它可能是一种进化适应，以防止害虫。一系列实验将测试单独生长生理学或防御反应的替代解释，使用在过去400年里在低水平或高水平昆虫攻击下分别进化的植物种群。这项工作将包括本科生的贡献。这项研究将检验植物-昆虫相互作用研究的基石，即最佳防御理论，该理论预测草食动物选择年轻组织比年老组织得到更好的保护。然而，生理上的限制，而不是对食草动物施加的选择的适应性反应，可能导致相同的模式。在这个提议中，我的目标是通过解开是适应性进化还是生理限制驱动了防御分配的差异，来推进对是什么驱使嫩叶如此高度防御的理解。为了测试生理约束与适应性进化的替代假设，将开发一个严格的最佳防御新框架，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，(3)评估这些值在生长季节中的变化。该框架将通过植物种群的种内比较来进行测试，这些植物种群在可预测的攻击风险方面存在差异（通过使用欧洲和北美的Verbascum thapsis母系），通过盆栽实验和组织价值（组织去除和种子输出）和化学防御分配来测量特定组织。

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.