A new perspective on amphibians under global change: Detecting sublethal effects of environmental stress as agents of silent population declines

由于栖息地破坏、持续的城市化和农业扩张等与人为全球变化相关的干扰，两栖动物处于全球生物多样性危机的前沿。但在没有受到这种直接干扰影响的栖息地，生物多样性也会丧失，这可能是由环境压力造成的，例如化学污染、病原体和持续的气候变化，导致种群稳步但沉默地下降。暴露在亚致死环境应激源会增加应激激素水平，但也可能影响形态、生理和免疫功能，对表现、健康和生存产生重要的遗留影响。在全球变化的现实中，两栖动物在所有生命阶段都暴露于同时发生的应激源，但研究应激源的相互作用的研究很少，关于两栖动物不同生命阶段的长期研究完全缺失，但需要估计亚致死应激对种群规模的影响。该项目旨在阐明亚致死环境应激源在神秘的两栖动物衰退中的作用，并开发一种早期预警工具，通过在两栖动物繁殖池塘中进行非侵入性应激激素测量来检测种群是否已经长期应激但尚未或潜伏地衰退。特别是，这个项目将通过分析形态、生理、内分泌、免疫和遗传生物标记物作为应激的合适替代指标来调查对热应激和硝酸盐污染的短期和长期反应。这项研究将集中在一种常见但逐渐衰落的无尾两栖动物物种--普通青蛙(Rana Temporaria)上。此外，本研究旨在确定该物种对应激条件的驯化潜力，并将有助于评估未来在全球变化面前的暂时性斑潜蝇的威胁。这项研究基于三个连续的部分：(A)荟萃分析，研究水生污染物和温度对两栖动物交互作用的经验知识；(B)三年多的实地研究，重点是不同硝酸盐污染物对幼虫和成虫应激激素水平的影响；(C)实验室研究，调查变态期间和变态后温度波动和硝酸盐污染对应激的各种生物标志物的影响。这项研究的结果将使我们能够通过检测应激的多个生物标志物来更全面地了解应激对环境变化的反应，并将为深入了解全球变化对两栖动物种群的亚致死效应提供见解，这些亚致死效应会潜移默化地影响两栖动物种群，导致衰退或适应。此外，这项研究的结果可以作为在其分布范围内临时雷公藤种群继续急剧下降之前采取适当的保护策略的基础。

Amphibians are at the forefront of the worldwide biodiversity crisis due to disturbances associated with anthropogenic global change such as habitat destruction, ongoing urbanization, and agricultural expansion. But biodiversity is also lost in habitats unaffected by such direct disturbances, possibly caused by environmental stressors such as chemical pollution, pathogens, and ongoing climate change resulting in steady but silent population declines. Exposure to sublethal environmental stressors increases the stress-hormone level but might also affect morphology, physiology, and immune functioning with important carry-over effects to performance, health, and survival. In global change reality, amphibians at all life stages are exposed to simultaneously occurring stressors but studies investigating interactive effects of stressors are rare and long-term studies on various life stages of amphibians are completely missing but needed to estimate sublethal stress effects on population scale.The proposed project aims to clarify the role of sublethal environmental stressors in enigmatic amphibian declines and to develop an early warning tool for detecting if populations are already chronically stressed but not yet or insidiously declining by noninvasive stress-hormone measurements in amphibian breeding ponds. In particular, this project will investigate short- and long-term responses to thermal stress and nitrate pollution by analyzing morphological, physiological, endocrinological, immunological, and genetic biomarkers as suitable proxies for stress. The study will focus on a common, but slowly declining anuran species, the common frog (Rana temporaria). Also, this study aims to determine the acclimation potential of this species to stressful conditions and will help to assess the future threat of R. temporaria in the face of global change. The study is based on three consecutive components: (A) a meta-analysis, studying the empirical knowledge on the interactive effects of aquatic contaminants and temperature on amphibians, (B) a field study over three years, focusing on the impact of different nitrate contaminations on stress-hormone levels in larval and adult R. temporaria, and (C) a laboratory study, investigating the effects of temperature fluctuations and nitrate pollution on various biomarkers of stress during and after metamorphosis. The results of this study will enable us to understand stress responses to changing environments more holistically by detecting multiple biomarkers of stress and will provide insights into sublethal effects of global change which affect amphibian populations insidiously resulting in either decline or adaptation. Further, the results of this study might serve as a basis for appropriate conservation strategies before populations of R. temporaria proceed to decline dramatically across its distribution range.