A key challenge for ecological risk assessment of contaminants under global warming is to predict effects at higher levels of biological organisation. One approach to reach this goal is to study how contaminants and warming cause changes in body stoichiometry as these may potentially cascade through food webs. Furthermore, though contaminants typically interact with warming, how rapid adaptation to higher temperatures affects these interactions is poorly studied. Here, we examined the effects of an important contaminant (ZnO nanoparticles, nZnO) and mild warming (4 °C) on body stoichiometry (C, N, P and their ratios) of an aquatic keystone species, the water flea Daphnia magna. To evaluate whether thermal evolution impacts the effects of nZnO at higher temperatures, we compared two sets of clones from a thermal selection experiment where Daphnia were kept in outdoor mesocosms at ambient or ambient +4 °C temperatures for 2 years. Exposure to nZnO decreased key body stoichiometric ratios (C:N, C:P and a trend for N:P) while warming increased the body C:N ratio. The stoichiometric changes to nZnO and warming were mostly independent and could be partly explained by changes in the macromolecules sugars and fat. Exposure to nZnO decreased C-rich sugars contributing to a reduced %C. Warming reduced body %C due to decreased C-rich sugars and fat levels, yet warming decreased body N% even more resulting in a higher C:N ratio. The stoichiometric responses to nZnO at the higher temperature did not differ between the two sets of clones, indicating experimental thermal evolution did not change the effects of nZnO under warming. Studying the stoichiometric responses to nZnO and warming of this keystone species may provide novel insights on the toxic effects of contaminants under warming. Moreover, understanding the influence of thermal evolution on the toxicity of contaminants is important for ecological risk assessment especially in a warming world.

中文翻译：

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热演化对升温下对纳米ZnO的化学计量响应的影响并不普遍：实验演化的见解。

在全球变暖下对污染物进行生态风险评估的一个关键挑战是预测更高水平的生物组织的影响。实现此目标的一种方法是研究污染物和变暖如何导致人体化学计量的变化，因为这些污染物和温度可能会通过食物网扩散。此外，尽管污染物通常与变暖相互作用，但对高温的快速适应如何影响这些相互作用的研究却很少。在这里，我们研究了重要污染物（ZnO纳米颗粒，nZnO）和温和升温（4°C）对水生梯形水蚤蚤蚤（Daphnia magna）的身体化学计量（C，N，P及其比率）的影响。要评估热演化是否会在较高温度下影响nZnO的影响，我们比较了来自热选择实验的两组克隆，其中水蚤在环境或环境温度+4°C的温度下在室外中型环境中保存2年。暴露于nZnO会降低人体的关键化学计量比（C：N，C：P和N：P的趋势），而变暖则会增加人体的C：N比率。nZnO和变暖的化学计量变化大部分是独立的，并且可以由大分子糖和脂肪的变化部分地解释。暴露于nZnO会降低富含C的糖，从而降低％C。由于减少富含C的糖和脂肪含量，变暖会降低身体的％C，而变暖会进一步降低身体的N％，从而导致更高的C：N比。两组克隆在较高温度下对nZnO的化学计量响应没有差异，表明实验的热演化并没有改变升温条件下nZnO的影响。研究对nZnO的化学计量响应和该基石物种变暖可能会为变暖下污染物的毒性作用提供新的见解。此外，了解热演化对污染物毒性的影响对于生态风险评估尤其重要，尤其是在变暖的世界中。