Collaborative Research: Did the Neogene aridification drive adaptive ecological radiation in an ancient plant lineage?

数亿年前进化而来的生物通常被认为是遗迹或“活化石”，因为它们似乎与已灭绝的化石祖先没有变化。在所有被认为是活着的文物的古代分类群中，苏铁尤其值得注意，因为最近的证据表明，现存的苏铁可能根本不是文物，而是在新近纪(约20万年前)进化的。这段时间的特点是气温下降，大气中二氧化碳浓度下降，干旱地区扩大。这项研究询问，随着苏铁在新的条件下进化出自己的解剖学和生理学，新近纪气候变化是否推动了苏铁的多样化。这种从细胞到整个植物的综合方法将为苏铁的进化提供一个新的视角，并测试这个古老的谱系在苏铁起源数亿年后是否在多个大陆经历了并行和并行的进化。这项拟议的工作尤其关键，因为苏铁是地球上最濒危的植物群之一，约70%的物种面临灭绝的威胁，主要是由于栖息地破坏和偷猎。也许没有其他植物谱系以如此惊人的速度消失，可以提供一个独特的机会来研究种子植物进化的最早实验之一，我们的结果将直接为保护实践提供指导。该项目将为威斯康星大学麦迪逊分校和佛罗里达国际大学的研究生和本科生提供研究经验，这两所大学是美国最大的拉美裔服务机构之一，以及为本科生提供以研究为导向的实地课程。这项研究将揭示产生现存多样性的生态和进化过程，苏铁是最古老和最不寻常的种子植物之一。为了确定苏铁的多样性是否是通过适应性特征进化实现的，该项目将：(A)表征苏铁解剖特征的多样性(例如气孔、束鞘延伸、输血组织和木质部的解剖特征)，并测试它们对非生物条件(例如光、二氧化碳、VPD、干旱)的气体交换和水力反应的影响，(B)测试这些解剖和生理特征是否与物种在气候空间的分布有关，以及(C)确定特征进化的时间和顺序是否与新近纪气候变化相对应。通过利用苏铁表现出的不同寻常的解剖特征组合，这项研究可能通过以下方式对植物生理学、生态学和进化产生深远的影响：(A)揭示在其他植物群(例如，束鞘延伸、输血组织)中也发现的功能鲜为人知的解剖特征(S)的重要性，(B)表征在现存植物中特别罕见但在已灭绝的分类群(例如，管胞和同质维管)中常见的特征组合的功能，从而允许对已灭绝谱系的功能进行新的洞察，并更好地为维管植物的生理特征进化序列提供背景，以及(C)测试关于进化的重复性和可预测性的长期假设。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Living organisms that evolved hundreds of millions of years ago are often considered relics or "living fossils" because they seem unchanged from their extinct, fossilized progenitors. Of all ancient taxa regarded as living relics, cycads are particularly notable because recent evidence suggests extant cycads may not be relics at all, but instead evolved during the Neogene period (~20My ago). This time period was characterized by declining temperatures, atmospheric CO2 concentrations, and the expansion of arid regions. This research asks whether Neogene climate change drove the diversification of cycads as they evolved their anatomy and physiology in response to the new conditions. This integrative approach that spans from cells to whole plants will provide a novel perspective on cycad evolution and test whether this ancient lineage experienced concurrent and parallel evolution on multiple continents hundreds of millions of years after the origin of cycads. The proposed work is especially critical because cycads are among the most endangered plant groups on Earth, with ~70% of species threatened with extinction, primarily due to habitat destruction and poaching. Perhaps no other lineage of plants disappearing at such an alarming rate can provide as unique an opportunity to examine one of the earliest experiments of seed plant evolution, and our results will directly inform conservation practices. This project will provide research experiences for graduate students and undergraduates at University of Wisconsin-Madison and Florida International University, one of the nation's largest Hispanic Serving Institutions, as well as research-driven field courses for undergraduates. This research will uncover the ecological and evolutionary processes that have generated the extant diversity of one of the oldest and most unusual groups of seed plants, the cycads. To determine whether Neogene diversification of cycads was enabled by adaptive trait evolution, the project will: (A) characterize the diversity of cycad anatomical traits (e.g. anatomical traits of stomata, bundle sheath extensions, transfusion tissue, and xylem) and test their impacts on gas exchange and hydraulic responses to abiotic conditions (e.g. light, CO2, VPD, drought), (B) test whether these anatomical and physiological traits are linked to species’ distributions in climate space, and (C) determine whether the timing and order of trait evolution corresponded to Neogene climate change. By leveraging the unusual anatomical trait combinations exhibited by cycads, this research may have far reaching impacts in plant physiology, ecology, and evolution by: (A) revealing the significance of anatomical traits with poorly known function(s) that are also found in other plant groups (e.g., bundle sheath extensions, transfusion tissue), (B) characterizing the function of trait combinations that are exceptionally rare among extant plants but commonly found in extinct taxa (e.g., tracheids and homogeneous pits) thus allowing new insight into the function of extinct lineages and better contextualizing the sequence of physiological trait evolution in vascular plants, and (C) testing long-standing hypotheses about the repeatability and predictability of evolution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.