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

化石证据表明，在陆地上形成宏观生态系统后不久，植物和昆虫就相互作用了，而食草动物--食用活的植物组织--是一种古老的策略，一直延续到大约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的复杂和重要组成部分。然而，只有机械防御已经研究了化石植物，因为化学防御是不容易评估的化石记录。现代研究表明，植物已经进化出两种主要的策略来对抗节肢动物。植物光合作用策略允许食草昆虫通过生产美味的、落叶的、寿命短的薄叶叶子来获取光合组织。另一方面，食草动物的防御策略是利用万年青的、硬叶的叶子，这些叶子具有很长的寿命，受到广泛的物理和化学威慑的高度保护。该项目的目标是利用固相微萃取气相色谱（SPME GC-MS）和飞行时间二次离子质谱（ToF-SIMS）分析保存完好的植物化石，以确定任何保存的化学防御痕迹，并了解化学防御的演变和发展。我们专注于三个保存异常完好的植物群：6700万年前的最新白垩纪地狱溪组，3.05亿年前的晚宾夕法尼亚卡尔霍恩煤的马通组，和3.82亿年前的泥盆纪卡茨基尔组。对这些化石的分析将与新鲜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。这个项目回答了关于化学防御的两个问题：1。什么样的化学物质参与了目标血统随时间的防御系统？2.是化学防御结构的形态（例如，毛状体和油体细胞）与它们所含的实际化学物质脱钩？此外，本研究中开发的方法可用于研究其他具有保护化学防御潜力的化石。

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.