Water-borne and plasma corticosterone are not correlated in spotted salamanders

Water-borne hormone measurement is a noninvasive method suitable for amphibians of all sizes that are otherwise difficult to sample. For this method, containment-water is assayed for hormones released by the animal. Originally developed in fish, the method has expanded to amphibians, but requires additional species-specific validations. We wanted to determine physiological relevance of water-borne corticosterone in spotted salamanders (Ambystoma maculatum) by comparing concentrations to those taken using established corticosterone sampling methods, such as plasma. Using a mixture of field and laboratory studies, we compared water-borne corticosterone levels to other traditional methods of sampling corticosterone for spotted salamander larvae, metamorphs, and adults. Despite multiple attempts, and detecting differences between age groups, we found no correlations between water-borne and plasma corticosterone levels in any age group. Water-borne sampling measures a rate of release; whereas plasma is the concentration circulating in the blood. The unique units of measurement may inherently prevent correlations between the two. These two methods may also require different interpretations of the data and the physiological meaning. We also note caveats with the method, including how to account for differences in body size and life history stages. Collectively, our results illustrate the importance of careful validation of water-borne hormone levels in each species in order to understand its physiological significance.水体激素检测法（water-borne hormone measurement）是一种无创检测手段，适用于体型各异且难以通过传统方式采样的两栖动物。该方法通过检测实验动物释放至饲养水体（containment-water）中的激素水平完成检测。该方法最初开发用于鱼类研究，后拓展至两栖动物领域，但仍需针对不同物种开展特异性验证。本研究旨在通过将斑点钝口螈（Ambystoma maculatum）的水体皮质酮（corticosterone）水平与血浆（plasma）等经典皮质酮采样方法获取的结果进行对比，明确水体激素检测法的生理相关性。本研究结合野外与实验室实验，对比了斑点钝口螈幼体、变态个体以及成体的水体皮质酮水平与传统皮质酮采样方法的检测结果。尽管进行了多次尝试并成功检测出不同年龄组间的激素水平差异，但我们未在任何年龄组中发现水体皮质酮与血浆皮质酮水平存在相关性。水体激素检测法衡量的是激素的释放速率，而血浆检测法反映的是血液中循环的激素浓度。二者独特的计量单位本质上可能导致无法建立相关性。此外，这两种检测方法对数据及生理意义的解读路径也存在差异。本研究同时指出了该方法的注意事项，例如如何校正体型与生活史阶段带来的检测差异。综上，本研究结果表明，若要明确水体激素检测结果的生理意义，针对每个物种开展严谨的验证工作至关重要。