The projected climate change and increase in thermal conditions in northern latitudes over the next 60 yr has the potential to alter the metabolic scope and potential fitness of aquatic ectotherms. Here, we experimentally tested if elevated egg incubation temperature affected metabolic scope in juvenile brown trout (Salmo trutta) as a phenotypically plastic response. Cohorts of brown trout from anadromous and resident crosses were raised through embryogenesis in either natural river temperatures (cold) or elevated (+3°C, warm) temperatures until they could feed exogenously. The standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope (AS = MMR − SMR) of juveniles from four anadromous‐resident crosses and from both incubation temperatures were tested at 13°C. We found that metabolic measures (SMR, MMR, AS) were lower in warm than cold‐incubated fish. There was no difference in the metabolic rates of fish from different anadromous‐resident crosses. The results of this experiment are consistent with the countergradient variation hypothesis (CGV) in which phenotypic variation, in this case variation in metabolic rates, is inversely related to thermal conditions, originally proposed in relation to altitudinal or latitudinal gradients. While previous studies have related CGV to genetic differences between populations, our study shows that thermal differences encountered at the embryonic stage can produce a phenotypic pattern consistent with CGV. It is difficult to predict the consequences of these metabolic changes in a future warmer climate, as lower metabolic rates indicate that brown trout will probably expend less energy, but a reduced aerobic scope may counteract this affect, limiting their ability as a top predator and in escaping predators. Our results suggest that there are mechanisms used to adjust to elevated water temperature that can be initiated during embryogenesis. Given that there were no differences among crosses, it is likely that temperature‐induced differences are the result of plastic responses.

中文翻译：

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胚胎发生过程中的热条件影响幼体鳟鳟鱼的代谢率

在接下来的60年中，预计的气候变化和北部纬度地区热状况的增加可能会改变新陈代谢的范围，并可能改变水等温线。在这里，我们通过实验测试了蛋孵化温度升高是否会影响少年鳟鱼的代谢范围（Salmo trutta）作为表型可塑性反应。在自然河水温度（冷）或高温（+ 3°C，温暖）下，通过胚胎发生饲养了来自杂种和常驻杂交的褐鳟，直到它们能够外生。在13°C下测试了四个非定居杂交和两个温育温度下的少年的标准代谢率（SMR），最大代谢率（MMR）和有氧范围（AS = MMR-SMR）。我们发现，温暖的鱼类的代谢指标（SMR，MMR，AS）低于冷孵化的鱼类。不同的无定居杂交鱼的代谢率没有差异。该实验的结果与反梯度变异假说（CGV）一致，其中表型变异，在这种情况下为代谢率的变异，与温度条件成反比，最初与温度梯度或纬度梯度有关。尽管先前的研究已将CGV与种群之间的遗传差异相关，但我们的研究表明，在胚胎期遇到的热差异可以产生与CGV一致的表型。很难预测这些代谢变化在未来气候变暖中的后果，因为较低的代谢率表明褐鳟可能消耗较少的能量，但是有氧运动能力的降低可能抵消这种影响，限制了它们作为顶级捕食者和捕食者的能力。逃避掠食者。我们的结果表明，有一些机制可用于调节水温升高，这种机制可在胚胎发生过程中引发。鉴于十字架之间没有差异，