The detection of antiherbivore secondary compounds in the fossil record and their potential role in defense against insects

化石证据表明，在宏观生态系统起源于陆地后不久，植物和昆虫就开始相互作用，而草食--消耗活的植物组织--是一种古老的策略，可以追溯到大约4.1亿年前的泥盆纪早期。因此，它们的相互作用是古代和现代生态系统复杂而重要的组成部分。然而，只对化石植物的机械防御进行了研究，因为在化石记录中很难评估化学防御。现代对反食草动物防御的研究表明，植物已经进化出两种主要的策略来对抗节肢动物草食动物。适应性策略允许昆虫草食动物通过生产寿命短的美味的、落叶的、薄叶的叶子来获取光合作用组织。另一方面，食草动物的防御策略是使用寿命长的常绿硬叶状叶子，这些叶子得到了广泛的物理和化学威慑的高度防御。该项目的目标是使用固相微萃取气相色谱(SPME GC-MS)和飞行时间二次离子质谱仪(ToF-SIMS)来分析保存完好的植物化石，以识别任何保存下来的化学防御痕迹，并了解化学防御的演变和发展。我们关注的是三个保存特别完好的植物群：6700万年前的最新白垩纪地狱溪组，3.05亿年前的马图恩组宾夕法尼亚晚期卡尔霍恩煤，以及3.82亿年前的泥盆纪卡茨基尔组。对这些化石的分析将与对新鲜的和腐烂的现代类似物以及已知参与现代化学防御的纯生物碱的分析进行比较。这个项目回答了两个关于化学防御的问题：1.随着时间的推移，目标谱系的防御系统涉及哪些化学物质？2.化学防御层(如毛状体和油体细胞)的形态是否与它们所含的实际化学物质脱钩？此外，这项研究中开发的方法也可以用于研究其他具有保存化学防御能力的化石。

Fossil evidence indicates that plants and insects were interacting soon after macroscopic ecosystems originated on land, and herbivory ‒ the consumption of living plant tissues ‒ is an ancient strategy that extends to the Early Devonian about 410 million years ago. As such their interactions are complex and important components of ancient and modern ecosystems. However, only mechanical defenses have been studied for fossil plants, since chemical defenses are not easy to assess in the fossil record. Modern studies of antiherbivore defenses indicate that plants have evolved two major strategies for contending with arthropod herbivores. The accommodationist strategy allows photosynthetic tissue to be accessed by insect herbivores by production of palatable, deciduous, thin-leaved foliage with short lifespans. The herbivore defensive strategy, on the other hand, is employs evergreen, sclerophyllous leaves with long lifespans that are highly defended by wide-ranging physical and chemical deterrents. The goal of this project is to use solid phase microextraction gas chromatography (SPME GC-MS) and time of flight secondary ion mass spectrometry (ToF-SIMS) to analyze well-preserved fossil plants to identify any preserved traces of chemical defenses, and to understand the evolution and development of chemical defenses. We are focusing on three exceptionally preserved floras: the 67 million-year-old latest Cretaceous Hell Creek Formation, the 305 million-year-old Late Pennsylvanian Calhoun Coal of the Mattoon Formation, and the 382 million-year-old Devonian Catskill Formation. The analyses of these fossils will be compared to analyses of fresh and decayed modern analogues and pure alkaloids known to be involved in modern chemical defenses. This project answer two questions about chemical defenses: 1. What chemicals were involved in the defense systems of the targeted lineages through time? 2. Is the morphology of the chemical defense strcutres (e.g., trichomes and oil body cells) decoupled from the actual chemicals they contain? Furthermore, the methods developed in this study can be used to study other fossils with the potential to preserve chemical defenses.