Climate warming impacts ecosystems through multiple interacting pathways, including via direct thermal responses of individual taxa and the combined responses of closely interacting species. In this study, we examined how warming and infection by an oomycete parasite (Saprolegnia) affect the dominant zooplankter of Russia's Lake Baikal, the endemic copepod Epischurella baikalensis. We used a combination of laboratory experiments, long‐term monitoring data, and population modeling. Experiments showed a large difference in the thermal optima of host and parasite, with strong negative effects of warm temperatures on E. baikalensis survival and reproduction and a negative effect of Saprolegnia infection on survival. Saprolegnia infection had an unexpected positive effect on E. baikalensis reproductive output, which may be consistent with fecundity compensation by females exposed to the parasite. Long‐term monitoring data suggested that Saprolegnia infections were most common during the warmest periods of the year. Population models, parameterized with experimental and literature data, correctly predicted the timing of Saprolegnia epizootics, but overestimated the negative effect of warming on E. baikalensis populations. Models suggest that diel vertical migration may allow E. baikalensis to escape the negative effects of increasing temperatures and parasitism and enable E. baikalensis to persist in the face of moderate warming of Lake Baikal. Our results contribute to understanding of how warming and parasitism interact to affect the pelagic ecosystems of cold lakes and oceans and how the consequences of these interacting stressors can vary seasonally, spatially, and interannually.

中文翻译：

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生病了吗？气候变暖和寄生虫对贝加尔湖主要浮游动物的影响

气候变暖通过多种相互作用的途径影响生态系统，包括通过单个分类单元的直接热响应以及紧密相互作用的物种的组合响应。在这项研究中，我们研究了卵菌寄生虫（腐殖体）的变暖和感染如何影响俄罗斯贝加尔湖的主要浮游动物，贝加尔湖是该地区的co足类动物Epischurella baikalensis。我们结合了实验室实验，长期监测数据和种群模型。实验表明，寄主和寄生虫的最佳温度差异很大，温暖的温度对贝加尔湖大肠杆菌的生存和繁殖具有强烈的负面影响，而腐殖质感染则对生存产生负面影响。腐烂病感染对贝加尔湖E. baikalensis的生殖产量具有出乎意料的积极影响，这可能与暴露于该寄生虫的雌性的生殖力补偿相一致。长期监测数据表明，在一年中最温暖的时期，腐烂症感染最为常见。用实验和文献数据进行参数化的种群模型可以正确预测腐烂腐生动物的发生时间，但高估了变暖对贝加尔山毛榉种群的负面影响。模型表明diel垂直迁移可能使白屈菜逃脱温度升高和寄生虫的负面影响，并使白屈菜继续面对贝加尔湖的温和增温。我们的结果有助于理解变暖和寄生虫如何相互作用以影响寒冷的湖泊和海洋的中上层生态系统，以及这些相互作用的压力源的后果如何在季节，空间和年度间变化。