CAREER: Tracking the evolution of grasses and grasslands: using phytoliths to explore evolution-ecology links in deep time

职业生涯：追踪草和草原的进化：使用植物硅体探索进化-生态联系的深度，华盛顿大学的Caroline Stromberg今天覆盖了地球40%的陆地表面，为包括人类在内的10亿多种动物提供了栖息地，并极大地影响了全球气候以及碳循环和二氧化硅循环。了解草原生物群的历史对于理清其复杂的控制和预测天然草原和农作物将如何应对持续的人类诱导的气候变化至关重要。近年来，对植物硅石化石(植硅体)的分析为草原形成过程中的进化和生态事件提供了迫切需要的信息。然而，要获得进一步的知识，关键在于确定化石记录中特定草类谱系的精确方法。这项职业研究有两个主要目标。首先，该项目将通过在进化框架中首次全面和详细地绘制草的植硅体形状图，以及绘制其他相关的功能特征(例如，光合作用途径)和环境偏好图，加强对植硅体的使用，以进行可靠的分类学(物种命名)和生态学解释。第二，该项目将利用这把草化石类型和生态学的“钥匙”来解决草进化中的两个突出问题：(1)草是在什么时候和什么环境中起源和多样化的？(2)是什么驱动了C4光合作用的草的生态扩张？为了解决第一个问题，该项目将研究来自阿根廷的白垩纪-古近纪(1.45亿-2300万年前)植硅体组合，以确定现存草之间的进化关系，并利用这些信息来确定谱系分裂发生的时间。植硅体组合分析和其他古植物学证据将有助于确定早期草的栖息地是什么样子。为了解决第二个问题，该项目将分析来自堪萨斯州的中新世-上新世(2300万-260万年前)植硅体组合，以记录大平原上C4草的生态扩张。该项目将推断目前存在的主要C4草种系，并重建植被结构的变化。直接与来自该剖面的稳定同位素数据进行比较，将可以测试哪些因素影响了C4草的优势地位。这一研究计划的结果将改变过去7000万年来生态系统变化的研究，特别是草原的聚集，并允许评估过去和未来是什么过程控制了草原的演变。它还将从根本上为考古学做出贡献，长期以来，植物硅体一直是追踪作物驯化和土地利用的主要工具。在这个研究项目中探索的综合主题--进化、生态和环境变化--将被纳入从中学到研究生水平的正式和非正式教育以及公共宣传。这一教育部分将通过(1)以探究为基础的实验室和我在华盛顿大学本科课程中的活动来完成，(2)在实验室和实地对一名博士后研究员、一名研究生和至少7名本科生进行研究指导，(3)在伯克博物馆设计新的展品，展示进化论研究的实践，以及(4)旨在吸引中学女生参与进化生态科学的课外计划。这里提出的联合研究和教育活动的目的是激发人们更多地欣赏塑造并继续塑造我们的世界的过程，更广泛地说，更好地理解所有年龄段的学生的科学实践和批判性思维。

CAREER: Tracking the evolution of grasses and grasslands: using phytoliths to explore evolution-ecology links in deep timeCaroline Stromberg, University of WashingtonGrasslands cover 40% of Earth's land surface today, provide habitats for over a billion animals including humans, and greatly influence global climate and the carbon and silica cycles. Understanding the history of the grassland biome is essential for disentangling its complex controls and predicting how natural grasslands and crop plants will respond to ongoing human induced climate change. In recent years, analysis of fossilized plant silica (phytoliths) has shed much needed light on evolutionary and ecological events during the establishment of grasslands. However, gaining further knowledge depends critically on refined methods for identifying specific grass lineages in the fossil record. This CAREER research has two main goals. First, the project will enhance the use of phytoliths for robust taxonomic (the naming of species) and ecological interpretations through the first comprehensive and detailed mapping of grass phytolith shapes in an evolutionary framework, coupled with mapping of other, functionally relevant traits (e.g., photosynthetic pathway) and environmental preferences. Second, project will use this "key" to fossil grass types and ecology to tackle two outstanding questions in grass evolution: (1) When and in what environments did grasses originate and diversify?; and (2) What drove the ecological expansion of grasses with C4 photosynthesis? To address the first question, the project will study Cretaceous-Paleogene (145-23 million years ago) phytolith assemblages from Argentina to determine the evolutionary relationships between the grasses present, and use this information to determine when the lineage split occurred. Phytolith assemblage analysis and other paleobotanical evidence will help determine what early grass habitats were like. To address the second question, the project will analyze Miocene-Pliocene (23-2.6 million years ago) phytolith assemblages from Kansas to document the ecological expansion of C4 grasses in the Great Plains. The project will infer major C4 grass lineages present, and reconstruct changes in vegetation structure. Direct comparison with stable isotopic data from the section will permit testing of which factors influenced the rise to dominance of C4 grasses. The results of this research program will transform the study of ecosystem change during the last ~70 million years, specifically the assembly of grasslands, and allow evaluation of what processes control grassland evolution, in the past and in the future. It will also contribute fundamentally to archaeology, where phytoliths have long been a principal tool for tracking domestication of crop plants and land use. The integrated themes explored in this research program--evolution, ecology, and environmental change--will be incorporated into formal and informal education at the middle-school- to graduate-school-level and public outreach. This educational component will be accomplished through (1) inquiry-based labs and activities in my undergraduate courses at University of Washington, (2) research mentoring of one postdoctoral researcher, one graduate student, and at least 7 undergraduates in the lab and field, (3) design of new exhibits at the Burke Museum demonstrating evolution research in action, and (4) an after-school program aiming to engage middle-school girls, which remain minorities in STEM, in evolution-ecology science. The joint research and educational activities proposed here aim to inspire a greater appreciation for the processes that shaped and continue to shape our world, and more broadly, a better understanding of the practice of science and critical thinking in students of all ages.