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

智力优势：人类活动正在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pH值，并改变溶解无机碳的浓度和组成。最近的研究表明，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。这些生理变化可能会对浮游植物的新陈代谢和群落结构产生深远的影响，同时也会对地球的碳循环产生影响，从而影响全球气候。然而，将目前的认识外推到该领域是复杂的，因为自然种群可能会因其不断变化的环境而演变，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，并且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席卷大量种群。该项目解决了浮游植物种群的两个主要领域的不确定性与以下问题：1）什么样的适应性突变，以升高的二氧化碳是很容易获得现存的物种，他们多久出现，以及有多大的影响是他们的健身？2)物理和生态的相互作用将如何影响这些突变扩展到常设种群？本研究将通过将海洋生态地球化学循环的实验演化与计算模拟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（如蓝藻，硅藻，颗石藻）的代表，将在模拟2100年CO2浓度下演变。从这些实验中，估计a）有益突变的比率，B）由这些突变赋予的适应性增益的大小，和c）次级表型（即，权衡）与这些突变相关，使用生理学和遗传学方法测定。第二，将修改现有的全球海洋系统的数值模型，以a）模拟不断变化的大气CO2浓度对海洋化学的影响，和B）允许将CO2特定的适应性突变体引入现有的虚拟浮游植物种群。该模型将用于探索有益突变在现实环境条件下（例如资源可用性，捕食等）的生态和生物地球化学影响。最初，该模型将被应用到理想化的敏感性研究，然后，实验结果变得可用，在我们的实验中观察到的特定有益突变的影响将被探讨。更广泛的影响：这一跨学科的研究将提供新的，变革性的理解在何种程度上进化过程影响浮游植物多样性，生理生态学，在不久的将来的海洋碳循环。许多重要成果之一将是开发和测试用于主要浮游植物功能群竞争研究的近乎中性的遗传标记，其应用范围远远超出目前的提议。拟议工作的一个固有组成部分是将教育和外联相结合，为本科生提供先进的跨学科培训，同时让他们和PI参与与海洋酸化有关的社区外联和教育。在密歇根州立大学，本科生将参加板凳工作以及计算机建模，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”与教育和推广计划使用。至少另外两名本科生将被招募到哥伦比亚和麻省理工学院从事该项目，重点是通过实践培训扩大对STEM的参与。此外，还将安排访问中学教育机构，讨论海洋酸化和微生物的进化。“这些访问将得到侧重于海洋酸化，微生物学和进化的教学资源的促进，这些资源可从两个NSF STC，BEACON（MSU）和CMORE（MIT/哥伦比亚）获得。

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).