Dissertation Research: A Field-Test of Damage-induced Alkaloidal Defenses in Wild Tobacco

草食动物诱导的植物防御已被充分记录，但缺乏这些诱导变化保护植物的实地证据。对野生烟草叶片生物碱含量的增加进行了研究。目前有足够的关于这种诱导防御系统的机理信息，可以对其生态意义进行实地试验。通过先前测试的实验设计，人工破坏生长在德克萨斯州南部的两组野生烟草植物，用激素抑制一组植物的生物碱反应，测量诱导和抑制植物维持的天然草食量及其各自的生物碱含量，将解决以下三个问题：1)这些损伤引起的生物碱水平是否起到了抗食草动物的防御作用？2)就生殖产出而言，这种诱导防御是否代价高昂？3)不同野生烟草种群之间的食草性是否存在差异，这种差异是否与这种诱导防御的收益（减少食草性）和成本（繁殖成本）的差异相关？本项目是为数不多的同时测量叶片化学和草食性表现的诱导植物抗性野外研究之一。此外，这是第一次通过抑制受损植物的防御来研究诱导防御的有效性，也是第一个测量防御繁殖成本的项目。

Herbivore-induced defense in plants is well documented, but field evidence that these induced changes protect plants is lacking. The damage-induced increases in leaf alkaloid content in wild tobacco will be studied. Currently enough mechanistic information on the workings of this induced defense system to propose a field test of its ecological significance is available. With a previously tested experimental design that involves artificially damaging two groups of wild Nicotiana repanda plants growing in south-Texas, hormonally supressing the alkaloidal respose in one group, measuring the amount of natural herbivory sustained by induced and suppressed plants and their respective alkaloid coantents, the following three questions will be addressed: 1) are these damage-induced alkaloid levels functioning as an antiherbivore defense? 2) is this induced- defense costly in terms of reproductive output? and 3) is there variation in herbivory between different populations of wild tobacco, and is this variation correlated with variation in the benefit (reduced herbivory) and cost (reproductive costs) of this induced defense? This project is one of the few field studies of induced plant resistance which simultaneously measures both leaf chemistry and herbivore performance. Moreover, it is the first time the efficacy of an induced defense has been studied by inhibiting the defense in damaged plants, and the first project to measure the reproductive cost of defense.