Collaborative Research: Seasonal and decadal changes in temperature drive Prochlorococcus ecotype distribution patterns

智力优势：海洋蓝藻原绿球藻的两种数量优势生态型在纬度上划分了海洋表面生态位，生态型eMIT9312在30°N-30°S区域占优势，eMED4在高纬度地区占优势。这些生态型可能占开阔海洋生态系统初级产量的25-50%，但这一比例取决于哪种生态型占主导地位。两种生态型的相对丰度与温度呈对数线性关系，从eMIT9312到eMED4的转变发生在~18°C。根据这些描述性数据，可以假设温度是相对丰度的主要驱动因素。然而，它们对净初级产量的贡献似乎与温度无关，这表明温度通过与光合作用无关的机制调节生态型优势。为了验证这些假设，pi正在进行一系列的实地和实验室研究，以调查温度变化对这些生态型分布的影响。北太平洋的两艘游轮将追踪eMIT9312-主导地区向emed4主导地区的转变，其中一艘游轮在冬季，另一艘在夏季。他们假设生态型丰度的比例将随着温度梯度的季节变化而向纬度移动：夏季18°C等温线向北的迁移将与1:1生态型过渡点的类似迁移相匹配。建议多次穿越18°C等温线，夏季游轮也将沿着等温线前往美国西海岸，以深入了解物理和地球化学的影响。将通过对收集的一系列物理、化学和生物数据进行一系列多变量分析，评估可能影响温度与生态型比之间关系的环境变量，如养分浓度、光照/混合深度和基于病毒/放牧的死亡率。季节性比较将辅以甲板孵育和实验室竞争分析（使用现有和新分离株），这将首次确定这些生态型的适合度系数与温度的关系。由于季节变暖期间温度梯度的纬度变化和生态型的迁移可能与气候变化导致的高纬度变暖具有共同特征，研究者的分析将为模拟生物和生物地球化学对气候变化的响应提供重要的生物学参数（如丰度、产量、温度变化系数）。这项研究将与承诺合作者的研究相结合，产生足够的数据，以在生态系统尺度上描述温度（相对于其他强迫因子）在限制这些数量上占主导地位的海洋光养生物的范围和季节性迁移方面的贡献。更广泛的影响：该提案包含了对整个科学界的几个层面的延伸。生物、化学和物理数据将存放在GenBank、NOAA的国家海洋数据中心以及生物和化学海洋数据管理办公室（BCO-DMO）。结果将为气候和生态系统变化模型提供信息，并作为海洋生态系统如何响应气候变化的例子在课堂上使用。这与分子生态学也有明确的联系：生物体基因组中潜在的微小变化是如何导致它们的生态或对气候变化的适应能力的根本差异的？该项目将通过为每次巡航建立正式的外展合作来扩大正在进行的努力。这些合作将基于两个具体目标：(1)一名科学新闻系学生将记录并广泛地传达巡航的目标和活动；(2)K-12教师的动手巡航机会将作为其他教师的信息门户。此外，该项目将支持三名研究生（两名在田纳西州- EPSCOR大学-一名在杜克大学）和几名本科生，组成各自论文的重要主体。最后，pi将继续努力为分子生态学和海洋科学中历史上代表性不足的群体提供机会。

Intellectual Merit: The two numerically-dominant ecotypes of the marine cyanobacterium Prochlorococcus partition the surface ocean niche latitudinally, with ecotype eMIT9312 dominant in the 30°N-30°S region and eMED4 dominant at higher latitudes. These ecotypes may account for 25-50% of primary production in open ocean ecosystems, but this percentage is dependent on which ecotype dominates. The relative abundance of the two ecotypes follows a log-linear relationship with temperature, with the transition from eMIT9312 to eMED4 occurring at ~18 °C. From these descriptive data, it has been hypothesized that temperature is the primary driver of relative abundance. Their contribution to net primary production, however, appears to be independent of temperature, suggesting temperature regulates ecotype dominance through photosynthesis-independent mechanisms. To test these hypotheses, the PIs are undertaking a series of field and lab studies to investigate the effect of temperature change on the distribution of these ecotypes. Two cruises in the North Pacific will trace the transitions from eMIT9312- to eMED4-dominated regions, with one cruise during the winter and the other during summer. They have hypothesized that the ratio of ecotype abundance will move latitudinally with the seasonal shift in temperature gradient: migration of the 18° C isotherm northward in the summer will be matched by a similar migration of the 1:1 ecotype transition point. Multiple crossings of the 18° C isotherm are proposed, and the summer cruise will also follow the isotherm to the Western US coast to gain insight on physical and geochemical influences. Environmental variables such as nutrient concentrations, light/mixing depths, and virus /grazing based mortality, which may impinge on the relationship between temperature and ecotype ratio, will be assessed through a series of multivariate analyses of the collected suite of physical, chemical and biological data. Seasonal comparisons will be complemented with on-deck incubations and lab competition assays (using existing and new isolates) that will establish, for the first time, how fitness coefficients of these ecotypes relate to temperature. As latitudinal shifts in temperature gradient and migration of ecotypes during seasonal warming likely share common features with high latitude warming as a consequence of climate change, the investigator's analyses will contribute important biological parameters (e.g., abundances, production rates, temperature change coefficients) for modeling biological and biogeochemical responses to climate change. This research will be integrated with that of committed collaborators, generating data sufficient for ecosystem-scale characterizations of the contributions of temperature (relative to other forcing factors) in constraining the range and seasonal migration of these numerically dominant marine phototrophs.Broader Impacts: This proposal encompasses several layers of outreach to the scientific community at large. Biological, chemical and physical data will be deposited in GenBank, NOAA's National Oceanographic Data Center, and the Biological and Chemical Oceanography Data Management Office (BCO-DMO). Results will inform climate and ecosystem-change models, and be used in classrooms as examples of how ocean ecosystems may change in response to climate variation. There are also clear connections to molecular ecology: how do potentially small changes in an organism's genome lead to fundamental differences in their ecology or resiliency to climate change? This project will expand ongoing efforts by establishing formal outreach collaborations for each cruise. These collaborations will be based on two specific goals: (1) a science journalism student will document and broadly communicate the goals and activities of the cruise and (2) a hands-on cruise opportunity for K-12 teachers will serve as an information gateway to other teachers. In addition, this project will support three graduate students (two at Tennessee - an EPSCOR university - and one at Duke) and several undergraduates, composing a significant body of their respective theses. Finally, PIs will continue their efforts to provide opportunities to historically under-represented groups in molecular ecology and ocean sciences.