Collaborative Research: Ocean Acidification: Impacts of evolution on the response of phytoplankton populations to rising CO2

智力价值：人类活动正以前所未有的速度推高大气中的二氧化碳浓度，扰乱海洋的碳酸盐缓冲系统，降低海洋的pH值，改变溶解的无机碳的浓度和组成。最近的研究表明，这种海洋酸化对浮游植物有许多短期影响，包括碳固定的变化等。这些生理变化可能对浮游植物的代谢和群落结构产生深远的影响，并对地球的碳循环产生伴随影响，从而对全球气候产生影响。然而，目前对该领域的理解的外推是复杂的，因为自然种群可能会随着环境的变化而进化，导致与短期研究预测的结果不同的结果。事实上，进化实验表明，微生物通常能够迅速适应环境的变化，有益的突变能够在与未来几十年环境动态预测相关的时间尺度上横扫大量种群。该项目解决了浮游植物种群的两个主要不确定性领域，包括以下问题：1)现存物种容易获得的对二氧化碳升高的适应性突变，它们出现的频率，以及它们对适应性的影响有多大？2)物理和生态的相互作用将如何影响这些突变向常住种群的扩展？本研究将通过将实验进化与海洋生物地球化学循环的计算模型相结合来解决这些问题。首先，培养的单细胞浮游植物，主要功能群的代表（如蓝藻、硅藻、球石藻），将在模拟的2100年二氧化碳浓度下进化。从这些实验中，我们将估算a)有益突变的比率，b)这些突变所带来的适应度增益的大小，以及c)与这些突变相关的次级表型（即权衡），并使用生理和遗传方法进行分析。其次，将修改现有的全球海洋系统数值模型，以a)模拟大气二氧化碳浓度变化对海洋化学的影响，b)允许将二氧化碳特异性适应突变体引入现有的虚拟浮游植物种群中。该模型将用于探索在现实环境情况下（例如资源可用性，捕食等）有益突变的生态和生物地球化学影响。最初，该模型将应用于理想化的敏感性研究；然后，随着实验结果的可用性，我们将探索实验中观察到的特定有益突变的含义。更广泛的影响：这项跨学科的研究将为进化过程影响浮游植物多样性、生理生态学和碳循环在不久的将来的海洋中的程度提供新颖的、变革性的理解。许多重要的成果之一将是开发和测试对主要浮游植物功能群竞争研究有用的近中性遗传标记，其应用远远超出目前的建议。拟议工作的一个固有组成部分是将教育和外展活动结合起来，向本科生提供先进的跨学科培训，同时让他们和专业人员参与与海洋酸化有关的社区外展活动和教育。在密歇根州立大学，本科生将参与实验和计算机建模，因此将获得跨学科的研究经验。在其他项目中，这些学生将制作一个简化版本的海洋建模软件，可以作为一个“应用程序”实施，用于教育和推广项目。至少两名本科生将被招募到哥伦比亚大学和麻省理工学院参与该项目，重点是通过实践培训扩大STEM的参与。此外，还将安排访问中等教育机构，讨论海洋酸化和微生物“在行动中的进化”。这些访问将由两个NSF STCs， BEACON （MSU）和CMORE （MIT/Columbia）提供的侧重于海洋酸化、微生物学和进化的教学资源提供。

Intellectual Merit: Human activities are driving up atmospheric carbon dioxide concentrations at an unprecedented rate, perturbing the ocean's carbonate buffering system, lowering oceanic pH, and changing the concentration and composition of dissolved inorganic carbon. Recent studies have shown that this ocean acidification has many short-term effects on phytoplankton, including changes in carbon fixation among others. These physiological changes could have profound effects on phytoplankton metabolism and community structure, with concomitant effects on Earth's carbon cycle and, hence, global climate. However, extrapolation of present understanding to the field are complicated by the possibility that natural populations might evolve in response to their changing environments, leading to different outcomes than those predicted from short-term studies. Indeed, evolution experiments demonstrate that microbes are often able to rapidly adapt to changes in the environment, and that beneficial mutations are capable of sweeping large populations on time scales relevant to predictions of environmental dynamics in the coming decades. This project addresses two major areas of uncertainty for phytoplankton populations with the following questions: 1) What adaptive mutations to elevated CO2 are easily accessible to extant species, how often do they arise, and how large are their effects on fitness? 2) How will physical and ecological interactions affect the expansion of those mutations into standing populations? This study will address these questions by coupling experimental evolution with computational modeling of ocean biogeochemical cycles. First, cultured unicellular phytoplankton, representative of major functional groups (e.g. cyanobacteria, diatoms, coccolithophores), will be evolved under simulated year 2100 CO2 concentrations. From these experiments, estimates will be made of a) the rate of beneficial mutations, b) the magnitude of fitness gains conferred by these mutations, and c) secondary phenotypes (i.e., trade-offs) associated with these mutations, assayed using both physiological and genetic approaches. Second, an existing numerical model of the global ocean system will be modified to a) simulate the effects of changing atmospheric CO2 concentrations on ocean chemistry, and b) allow the introduction of CO2-specific adaptive mutants into the extant populations of virtual phytoplankton. The model will be used to explore the ecological and biogeochemical impacts of beneficial mutations in realistic environmental situations (e.g. resource availability, predation, etc.). Initially, the model will be applied to idealized sensitivity studies; then, as experimental results become available, the implications of the specific beneficial mutations observed in our experiments will be explored.Broader Impacts: This interdisciplinary study will provide novel, transformative understanding of the extent to which evolutionary processes influence phytoplankton diversity, physiological ecology, and carbon cycling in the near-future ocean. One of many important outcomes will be the development and testing of nearly-neutral genetic markers useful for competition studies in major phytoplankton functional groups, which has applications well beyond the current proposal. An inherent component of the proposed work is the integration of education and outreach to provide advanced interdisciplinary training to undergraduate students, while involving both them and the PIs in community outreach and education related to ocean acidification. At MSU, undergraduate students will participate in bench work as well as computer modeling, and will therefore gain interdisciplinary research experience. Among other projects, these students will produce a simplified version of the ocean modeling software that may be implemented as an "app" for use with education and outreach programs. At least two additional undergraduates will be recruited to work on the project at Columbia and MIT, with a focus on broadening participation in STEM through hands-on training. Additionally, visits with secondary education institutes will be arranged to talk about ocean acidification and microbial "evolution in action." These visits will be facilitated by instructional resources focused on ocean acidification, microbiology, and evolution, which are available from two NSF STCs, BEACON (MSU) and CMORE (MIT/Columbia).