Physiological biomarkers are commonly used to assess the health of taxa exposed to natural and anthropogenic stressors. Glucocorticoid (GC) hormones are often used as indicators of physiological stress in wildlife because they affect growth, reproduction and survival. Increased salinity from human activities negatively influences amphibians and their corticosterone (CORT; the main amphibian GC) physiology; therefore, CORT could be a useful biomarker. We evaluated whether waterborne CORT could serve as a biomarker of salt stress for three free-living amphibian species that vary in their sensitivity to salinity: boreal chorus frogs (Pseudacris maculata), northern leopard frogs (Rana pipiens) and barred tiger salamanders (Ambystoma mavortium). Across a gradient of contamination from energy-related saline wastewaters, we tested the effects of salinity on baseline and stress-induced waterborne CORT of larvae. Stress-induced, but not baseline, CORT of leopard frogs increased with increasing salinity. Salinity was not associated with baseline or stress-induced CORT of chorus frogs or tiger salamanders. Associations between CORT and salinity were also not related to species-specific sensitivities to salinity. However, we detected background environmental CORT (ambient CORT) in all wetlands and spatial variation was high within and among wetlands. Higher ambient CORT was associated with lower waterborne CORT of larvae in wetlands. Therefore, ambient CORT likely confounded associations between waterborne CORT and salinity in our analysis and possibly influenced physiology of larvae. We hypothesize that larvae may passively take up CORT from their environment and downregulate endogenous CORT. Although effects of some hormones (e.g. oestrogen) and endocrine disruptors on aquatic organisms are well described, studies investigating the occurrence and effects of ambient CORT are limited. We provide suggestions to improve collection methods, reduce variability and avoid confounding effects of ambient CORT. By making changes to methodology, waterborne CORT could still be a promising, non-invasive conservation tool to evaluate effects of salinity on amphibians.

中文翻译：

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评估皮质酮作为暴露于盐度和环境皮质酮增加的两栖动物的生物标志物

生理生物标志物通常用于评估暴露于自然和人为压力源的分类群的健康状况。糖皮质激素 (GC) 激素通常用作野生动物生理压力的指标，因为它们会影响生长、繁殖和生存。人类活动导致的盐度增加会对两栖动物及其皮质酮（CORT；主要的两栖动物 GC）生理产生负面影响；因此，CORT 可能是一种有用的生物标志物。我们评估了水性 CORT 是否可以作为对盐度敏感度不同的三种自由生活两栖动物的盐胁迫生物标志物：北方合唱蛙 (Pseudacris maculata)、北方豹蛙 (Rana pipiens) 和斑纹虎蝾螈 (Ambystoma mavortium ）。跨越与能源相关的含盐废水的污染梯度，我们测试了盐度对幼虫基线和应激诱导的水性 CORT 的影响。压力引起的，但不是基线，豹蛙的 CORT 随着盐度的增加而增加。盐度与合唱蛙或虎蝾螈的基线或压力诱导的 CORT 无关。CORT 与盐度之间的关联也与物种特异性对盐度的敏感性无关。然而，我们在所有湿地中检测到背景环境CORT（环境CORT），并且湿地内部和湿地之间的空间变化很大。较高的环境 CORT 与湿地中幼虫的较低水性 CORT 相关。因此，在我们的分析中，环境 CORT 可能混淆了水性 CORT 和盐度之间的关联，并可能影响幼虫的生理。我们假设幼虫可能会被动地从环境中吸收 CORT 并下调内源性 CORT。虽然一些激素（如雌激素）和内分泌干扰物对水生生物的影响已经得到很好的描述，但调查环境 CORT 的发生和影响的研究是有限的。我们提供改进收集方法、减少可变性和避免环境 CORT 的混杂影响的建议。通过改变方法，水性 CORT 仍然可能是一种有前途的非侵入性保护工具，用于评估盐度对两栖动物的影响。减少变异性并避免环境 CORT 的混杂影响。通过改变方法，水性 CORT 仍然可能是一种有前途的非侵入性保护工具，用于评估盐度对两栖动物的影响。减少变异性并避免环境 CORT 的混杂影响。通过改变方法，水性 CORT 仍然可能是一种有前途的非侵入性保护工具，用于评估盐度对两栖动物的影响。