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There’s something in the water: validating a non-invasive stress hormone assay for tadpoles

There’s something in the water: validating a non-invasive stress hormone assay for tadpoles

Lynne Beaty


The physiological mechanisms underlying the effect of stressors on individual differences in animal behavior are poorly understood. This gap is due, in part, to the difficulty of repeatedly measuring physiological characteristics without causing additional undo stress to animals. This problem is exacerbated for small-bodied animals from which it is difficult to extract sufficient volume of biological material to accurately quantify aspects of individual physiology, like stress hormones. One way to circumvent this quandary, at least in aquatic organisms, is to assay the release rate of stress hormones into water. While water-borne stress hormone assays are commonly used in fish, this approach has yet to be validated in small-bodied aquatic amphibians, like tadpoles. Furthermore, because there are conflicting results for the relationship between tadpole stress hormones and activity levels, we investigated the relationship between stress hormones (corticosterone – CORT) and activity level in cricket frog (Acris blanchardi) tadpoles. After exposing tadpoles to exogenous CORT, we quantified whole-body and water-borne CORT release rates using EIA kits. We found that CORT levels were related to activity and that whole-body and water-borne CORT were positively correlated, validating the use of non-invasive water-borne assays for measuring CORT in small-bodied tadpoles. This was the first study to successfully validate this method for tadpoles, which will allow future studies to effectively and repeatedly quantify tadpole stress hormone levels and their relationship with purportedly stress-induced changes in behavior.