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

智力优势：海洋蓝藻原氯球菌的两种数量优势生态型在纬度上划分了表层海洋生态位，在30°N-30°S地区生态型eMIT9312占优势，在高纬度地区生态型eMED4占优势。这些生态型可能占公海生态系统初级生产力的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向eMED4的转变发生在~18℃。然而，它们对净初级生产力的贡献似乎与温度无关，这表明温度通过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正在进行一系列的野外和实验室研究，以调查温度变化对这些生态型分布的影响。北太平洋的两次巡航将跟踪从eMIT9312到eMED4主导地区的过渡，一次在冬季，另一次在夏季。他们假设，生态型丰度比将随着温度梯度的季节性变化而在纬度上移动：夏季18℃等温线向北迁移将与1：1生态型转换点的类似迁移相匹配。建议多次穿越18°C等温线，夏季邮轮也将沿着等温线前往美国西部海岸，以深入了解物理和地球化学影响。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来评估环境变量，如营养浓度、光照/混合深度和基于病毒/放牧的死亡率，这些变量可能影响温度和生态型比率之间的关系。季节性比较将与甲板孵化和实验室竞争分析(使用现有的和新的分离物)相补充，这将首次确定这些生态型的适合度系数与温度的关系。由于季节性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，研究人员的分析将为模拟生物和生物地球化学对气候变化的反应提供重要的生物学参数(例如丰度、生产率、温度变化系数)。这项研究将与坚定的合作者的研究相结合，产生足够的数据来描述温度(相对于其他强迫因素)在限制这些数量上占主导地位的海洋生物的范围和季节性迁徙方面的贡献，从而产生足够的数据。生物、化学和物理数据将存放在GenBank、NOAA的国家海洋数据中心和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，并在课堂上用作海洋生态系统如何应对气候变化的例子。分子生态学也有明显的联系：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发生根本变化的？该项目将通过为每艘邮轮建立正式的外联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)科学新闻专业的学生将记录并广泛传播邮轮的目标和活动，(2)为K-12教师提供的动手邮轮机会将成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，一所EPSCoR大学，一名在杜克大学)和几名本科生，构成他们各自论文的重要组成部分。最后，私人投资机构将继续努力，为分子生态学和海洋科学领域历来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.