Performance and fitness consequences of hypoxia and thermal stress in fishes

如果种群数量下降，没有足够的时间适应，或者如果捕食/竞争的减少使种群能够在不适应当地条件的情况下生存，无论是自然的还是人为的环境压力都可能限制当地适应。缺氧（低溶解氧，DO）是废物和肥料流入导致内陆和沿海水域加速富营养化和污染的人为压力的一种严重和广泛表现。在严重缺氧的情况下，氧气可能是与健身相关的表现特征的一个强大限制因素，比如耐力游泳或逃离捕食者。气候变化可能加剧缺氧对鱼类的影响，因为氧溶解度随着温度升高而降低，而变温动物（冷血生物）的代谢增加。相反，缺氧可能通过限制在较高温度下的有氧运动而加剧热应激。我们对来自低氧沼泽和常氧河流/湖泊的东非鱼类的研究表明，DO是种群之间与氧摄取相关特征差异的强大驱动因素。在比较低do和高do地区的种群时，我们记录了低do地区的鱼有更大的鳃、更大的头（以适应更大的鳃）和更强的缺氧耐受性。尽管有强有力的证据表明种群适应当地环境，但我们最近的研究表明，形态生理特征的适应性差异可能不会对低do鱼类产生积极的适应性影响。本研究计划将在这些基础研究的基础上，将鱼类的形态学和生理学与生态学和进化相结合，以了解缺氧对性能和适应性的影响，以及缺氧与热应激的相互作用。我们将结合野外调查和温度梯度，实验室驯化和饲养研究，以及野外实验来(a)测试一系列关于缺氧和热应激对性能和适应性的交互影响的预测，以及(b)测试局部适应自然界极端缺氧的特征。通过探索局部适应模式的潜在例外情况，量化缺氧和热应激之间的相互作用，我们可以更全面地了解环境应激源的生态和进化后果，并确定生物在极端环境中或面对环境变化时可能促进持久性的特征。**

Environmental stress, whether natural or human-induced, may constrain local adaptation if populations decline, have not had sufficient time to adapt, or if reduced predation/competition allows populations to persist despite poor adaptation to local conditions. Hypoxia (low dissolved oxygen, DO) is a serious and widespread manifestation of anthropogenic stress to inland and coastal waters driven by influx of wastes and fertilizers that accelerate eutrophication and pollution. Under severe hypoxia, oxygen can be a powerful limiting factor on fitness-related performance traits, such as endurance swimming or escaping predators. Climate change is likely to exacerbate the impacts of hypoxia on fishes, because oxygen solubility decreases with rising temperature while metabolism of ectotherms (cold-blooded organisms) increases. Conversely, hypoxia may exacerbate thermal stress by limiting aerobic performance at higher temperatures. Our studies of East African fishes from hypoxic swamps and normoxic river/lake sites have demonstrated that DO is a strong driver of divergence among populations in traits related to oxygen uptake. In comparisons of populations from low-DO and high-DO sites we have documented larger gills, larger heads (to accommodate larger gills), and greater tolerance to hypoxia in fish from low-DO sites. Despite this strong evidence that populations are adapted to their local environments, our recent studies suggest that adaptive divergence in morpho-physiological traits may not have positive fitness consequences in low-DO fish. This research program will build on these foundational studies, integrating the morphology and physiology of fishes with their ecology and evolution to understand performance and fitness consequences of hypoxia and the interaction of hypoxia with thermal stress. We will blend field surveys across DO and temperature gradients, lab acclimation and rearing studies, and field experiments to (a) test a series of predictions on interactive effects of hypoxia and thermal stress on performance and fitness and (b) test for signatures of local adaptation to extreme hypoxia in nature. By exploring potential exceptions to expected patterns of local adaptation and quantifying interactions between hypoxia and thermal stress, we can more fully understand the ecological and evolutionary consequences of environmental stressors and identify characteristics of organisms that may facilitate persistence in extreme environments or in the face of environmental change. **