Hypoxia in a warming world: performance and fitness consequences of dual stressors for inland fishes

除了过度捕捞和物种入侵外，淡水生物还面临着与土地转换、污染和富营养化相关的多重威胁。此外，越来越多的证据表明，淡水对气候变化高度敏感。最终，为了了解和预测人类活动对水生生物多样性的影响，我们必须探索多种压力因素的独立和相互作用的影响。缺氧（低溶解氧，DO）是水生系统中广泛存在的应激源，由可加速富营养化的废物和肥料的流入驱动;严重缺氧可能是鱼类性能的强大限制因素。气候变暖可能会加剧缺氧，因为鱼类的新陈代谢和氧气需求随着水温的增加而增加，而缺氧则限制了氧气的供应。这些双重压力源之间的潜在相互作用一直是最近几项研究的重点;其中许多研究都集中在短期（天，周）的鱼类暴露于一个或两个压力源。在这项研究计划中，我们将量化短期和终身（饲养研究）鱼类暴露于不同温度和DO制度的性能和健身后果;我们将探讨不同温度和DO制度的鱼类种群如何在其反应中有所不同。我们将建立在我们对东非鱼类的30年研究基础上，这些鱼类跨越自然界中强烈的温度和DO梯度。对田间种群的生态生理学测定和实验室驯化和饲养研究的组合将用于（a）测试温度上限的氧依赖性;（B）量化缺氧和热应激对性能和健身相关性状的相互作用;和（c）测试对缺氧的局部适应（例如，更大的鳃）提高对变暖的沃茨的耐受性。我们将研究跨越温度和溶解氧自然梯度的种群，以及那些经历溶解氧或温度变化以应对人类影响的种群，例如可以增加水温的森林砍伐或可以减少溶解氧的富营养化。解开多重压力源的影响是地球仪鱼类种群保护和管理的一个关键挑战。我们在非洲的长期实地系统使我们能够根据长期数据和综合研究，测试缺氧和热应力对鱼类的独立和相互作用影响的具体预测。通过混合种群间研究，长期环境数据和饲养实验，我们将在受控实验室条件下和自然界中的双重压力源的影响之间提供急需的联系。现场与实验室效果的一致性加强了我们在气候变化面前预测全球缺氧危机后果的能力，所获得的知识将有助于我们研究和管理本地和国外的系统。

Freshwater organisms face multiple threats associated with land conversion, pollution, and eutrophication, in addition to overharvesting and species invasions. In addition, there is mounting evidence that freshwaters are highly sensitive to climate change. Ultimately, to understand and predict effects of human activities on aquatic biodiversity, we must explore both independent and interactive effects of multiple stressors. Hypoxia (low dissolved oxygen, DO) is a widespread stressor in aquatic systems driven by influxes of wastes and fertilizers that can accelerate eutrophication; and severe hypoxia can be a powerful limiting factor on fish performance. Climate warming is likely to exacerbate hypoxia because fish metabolism and therefore oxygen demand increase with water temperature, while hypoxia limits oxygen supply. Potential interactions between these dual stressors have been the focus of several recent studies; many of which have focused on short-term (days, weeks) exposures of fish to one or both stressors. In this research program, we will quantify performance and fitness consequences of both short-term and life-long (rearing studies) exposure of fish to different temperature and DO regimes; and we will explore how fish populations from different temperature and DO regimes differ in their response. We will build on our 30-yr foundation of studies on East African fish species that cross strong gradients of temperature and DO in nature. A combination of ecophysiological assays on field populations and lab acclimation and rearing studies will be used to (a) test for oxygen dependency of upper thermal limits; (b) quantify interactive effects of hypoxia and thermal stress on performance and fitness-related traits, and (c) test whether local adaptation to hypoxia (e.g., larger gills) improves tolerance to warming waters. We will study populations crossing natural gradients of temperature and DO, and those experiencing change in DO or temperature in response to human impacts, such as deforestation that can increase water temperature or eutrophication that can decrease DO. Disentangling effects of multiple stressors is a key challenge to conservation and management of fish populations across the globe. Our long-term field system in Africa allows us to test specific predictions on independent and interactive effects of hypoxia and thermal stress on fishes based on long-term data and integrative research. By blending interpopulational studies, long-term environmental data, and rearing experiments, we will provide a much needed link between effects of dual stressors under controlled lab conditions and in nature. Consistency in field versus lab effects with strengthen our ability to predict consequences of the global hypoxia crisis in the face of climate change, and knowledge gained will help us to study and manage systems locally and abroad.