Evaluating corticosterone as a biomarker for amphibians exposed to increased salinity and ambient corticosterone

Abstract

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.

Testing whether adrenal steroids mediate phenotypic and physiologic effects of elevated salinity on larval tiger salamanders

“…We followed the exact methods of Tornabene et al . (2021b,c) to collect baseline and stress‐induced waterborne CORT. Briefly, to quantify baseline CORT on each sampling day, we placed larvae into fresh 950 mL polypropylene containers with 200 mL of fresh respective treatment solutions for 1 h. To minimize handling stress, larvae were transferred between treatment and collection containers using a nylon mesh net and gloved hand for <1 min.…”

“…Then, to quantify stress‐induced CORT, larvae were immediately placed in new containers with fresh respective treatment water; the container and larvae were shaken by hand for 5 min, and then larvae sat in containers for another 55 min (1 h total; Tornabene et al . 2021b,c). We also followed the exact methods of Tornabene et al .…”

“…For baseline and stress‐induced CORT, we weighted CORT samples in models by their coefficient of variance (CV) during quantification (between duplicate samples in EIAs; Tornabene et al . 2021b,c). Thus, measurements with high CV would be less heavily weighted in the model and vice versa.…”

“…2018; Tornabene et al . 2021c). We had 3 main objectives to test the effects of salinity on this widespread amphibian species.…”

A Review of Non-Invasive Sampling in Wildlife Disease and Health Research: What’s New?

“…This may in itself alter the cortisol excretion, both systemically and locally in the skin [152]. A further method for the minimally invasive assessment of steroid hormones in amphibians and fish is the immersion of caught individuals in a clean tank of water for a predetermined period of time, after which the animal is moved and excreted hormones can be extracted from the water [159][160][161][162]. These assays can also be used on environmental water samples; however, ambient cortisol and metabolites as well as steroid hormones may persist in the environment to varying degrees and limit the information that can be gathered about an individual in, for example, a pond [162].…”