Biochemical Changes in Aquatic Organisms in a Warming World

我们的世界正在变暖，但我们并不完全理解这一影响深远、具有全球意义的事件的后果。植物和动物对水温升高的反应是通过所谓的等粘适应过程来调整细胞膜的化学成分。这种生物化学适应涉及以多不饱和脂肪酸（PUFA）为代价增加饱和脂肪酸的量。随着水的升温，PUFA的损失，特别是ω-3长链PUFA（LC-PUFA;即20和22个碳长）的损失，对所有生命都有巨大的影响。浮游植物占全球初级生产总量的一半以上，是omega-3 LC-PUFA的主要生产者。然而，我们还不知道气候变暖将如何影响这些基本化合物的生产（来源）和分布（命运）。气候建模者预测，地表气温和极端高温日数将增加;地表水温也将随之增加（特别是在浅水生产系统中）。预计温带和北方地区将感受到最强烈的温度上升。在这些地区（水温较低，全民脂肪酸产量较高），有大量（> 100万）小型湿地（与陆地生态系统高度连通），这表明在生物圈的这些地区，淡水产生的LC-PUFA产量最大。大量证据表明，omega-3 LC-PUFA对动物的健康和福祉至关重要，支持提高生长速度和生殖能力，并以积极的方式促进心血管，免疫和认知健康。动物可以简单地从短链（即18碳）脂肪酸前体合成LC-PUFA，然而，对各种鱼类和哺乳动物（包括人类）的研究表明，将18碳omega-3 FA转化为LC-PUFA，如EPA（20：5 n-3）和DHA（22：6 n-3）是“不可靠和有限的”，因此在脊椎动物大脑，神经组织，心血管系统，视网膜，精子和牛奶中发现的大多数必需脂肪酸（EFA）来自饮食。Omega-3 LC-PUFA（如EPA和DHA）不是由陆生植物或昆虫产生的。因此，陆地生物最终从水生生物（例如昆虫羽化;鱼类）获得大部分ω-3 LC-PUFA，而水生生物又从藻类获得它们。这种“预制”的EFA来源是陆生（和水生）动物获得这些基本生物化学物质的最有效途径，其数量足以使它们保持在最佳状态。使用实验室和实地研究，我的学生（1个PDF，2个博士和1个硕士）和我以及我的同事将解决关键的知识差距，从而改变我们对气候变暖如何影响水生来源的omega-3 LC-PUFA的生产和再分布的理解。我们将：1）在受控的实验室条件下，量化生物化学相关脂质类中PUFA的产生（例如磷脂、二酰基甘油）作为水的函数在来自几个代表性分类群的几个世界性藻类物种中，和2）温和地加热天然池塘的部分，并测量藻类中PUFA的内部生产及其向浮游动物和昆虫幼虫阶段的营养转移，以及通量。LC-PUFA（再分布）从池塘到邻近的陆地系统（通过昆虫出现）。这种关于气候变化如何影响LC-PUFA生产的新概念将从根本上改变我们对水产资源所发挥的关键作用以及这种作用在变暖的世界中如何改变的认识。

Our world is warming up yet we do not fully understand the ramifications of this far-reaching, globally-significant, event. Plants and animals respond to increasing water temperature by adjusting the chemical composition of their cell membranes through the process known as homeoviscous adaptation. This biochemical adaptation involves increasing the amount of saturated fatty acids at the expense of polyunsaturated fatty acids (PUFA). The loss of PUFA as water heats up, particularly the loss of omega-3 long-chain PUFA (LC-PUFA; i.e. 20- and 22-carbons long), has enormous implications for all life. Phytoplankton contribute >½ of the total primary production globally and are the main producers of omega-3 LC-PUFA. However, we do not yet understand how climate warming will affect the production (source) and distribution (fate) of these essential compounds. Climate modelers predict an increase in surface air temperatures and in the number of extreme heat days; with concomitant increases in surface water temperatures (especially in shallow productive systems). These temperature increases are expected to be most profoundly felt in temperate and northern regions. The large (> 1 million) number of small wetlands (with high connectivity to terrestrial ecosystems) in these regions (where water temperatures were colder and EFA production was high) suggest that it is in these regions of the biosphere that freshwater-derived LC-PUFA are being produced in the greatest quantities. A large body of evidence demonstrates that omega-3 LC-PUFA are critical for the health and well-being of animals, supporting enhanced growth rates and reproductive capacities and contributing in demonstratively-positive ways to cardiovascular, immunologic, and cognitive health. Animals could simply synthesize LC-PUFA from shorter-chain (i.e. 18-carbon) fatty acid precursors, however, studies with a variety of fishes and mammals (including humans) have demonstrated that the conversion of 18-carbon omega-3 FA to LC-PUFA such as EPA (20:5n-3) and DHA (22:6n-3) is “unreliable and restricted” and that therefore the majority of the essential fatty acids (EFA) found in the vertebrate brain, nervous tissue, cardiovascular system, retina, sperm and milk come from the diet. Omega-3 LC-PUFA like EPA and DHA are not produced by terrestrial plants or insects. Thus, terrestrial organisms ultimately obtain much of their omega-3 LC-PUFA from aquatic organisms (e.g. insect emergence; fish) which, in turn, obtain them from algae. This “pre-formed” source of EFA is the most efficient way for terrestrial (and aquatic) animals to obtain these essential biochemicals in amounts sufficient to maintain them in optimal condition. Using lab and field studies, my students (1 PDF, 2 PhD and 1 MSc) and I, and my colleagues, will address critical knowledge gaps thereby transforming our understanding of how climate warming affects the production and re-distribution of aquatic-derived omega-3 LC-PUFA. We will: 1) quantify, under controlled laboratory conditions, the production of PUFA in biochemically-relevant lipid classes (e.g. phospholipids, diacylglycerols) as a function of water in several cosmopolitan algal species from several representative taxa, and 2) gently warm portions of natural ponds and measure both the internal production of PUFA in algae and their trophic transfer to zooplankton and the larval stages of insects and also the flux of LC-PUFA (redistribution) from the ponds onto adjacent terrestrial systems (via insect emergence). This new conceptualization of how climate change affects LC-PUFA production will fundamentally transform our appreciation of the key role that our aquatic resources play and how this role may be altered in a warming world.