Are glucocorticoids good indicators of disturbance across populations that exhibit cryptic variation in contaminant tolerance?

Abstract

Glucocorticoids (corticosterone/cortisol; cort) are frequently used in conservation as biomarkers of disturbance in wild populations. However, the context-dependent nature of cort means that it may not always accurately reflect disturbance. For example, there is growing evidence that wildlife populations can evolve or acclimate to human-induced environmental change (i.e. contaminants) by expressing higher levels of tolerance. Mechanisms that allow for populations to achieve higher contaminant tolerance can be related to cort and thereby impact the reliability of cort as an indicator of disturbance. This study asks: (1) do wildlife populations that differ in tolerance to contaminants differentially express baseline and stress-induced cort and ( 2) is cort a viable indicator of disturbance across populations that differ in tolerance to contaminants? Toward this goal, we identified three wood frog Rana sylvatica populations with relatively high NaCl tolerance and three populations with relatively low NaCl tolerance. Tadpoles from these populations were reared to metamorphosis in either an environmentally relevant concentration of NaCl (0.5 g L À1 NaCl) or a control (0 g L À1 NaCl). At metamorphosis we used a noninvasive waterborne assay to measure baseline and stress-induced cort release rates and measured fitness-related metrics. We found that contaminant tolerance influences cort levels. More tolerant populations had lower baseline cort and higher fitness compared to less tolerant populations. However, despite variation in cort across populations with different levels of tolerance, cort still represents a viable indicator of condition as our results show a consistent negative relationship between cort and fitness. Lastly, we found that levels of cort were consistent regardless of whether amphibians were reared in NaCl contaminated or noncontaminated environments. Overall, we emphasize the importance of recognizing population-level variation in cort due to contaminant tolerance when using cort as a biomarker for conservation purposes.

Native species exhibit physiological habituation to invaders: a reason for hope

“…There has been substantial work on how wild animals adjust their behaviour to HIREC [27,28], but do wild animals also adjust their physiological stress response to cope with HIREC? A growing number of studies have explored the diverse effects of human-induced environmental changes on GCs in amphibians, reptiles, birds and mammals [29][30][31][32][33][34][35]. However, these studies almost always focus on how average GCs are affected by anthropogenic disturbances at one point in time, and only few studies have explored the role of invasive species in eliciting a stress response in native species [36][37][38][39][40][41].…”

Framework for multi-stressor physiological response evaluation in amphibian risk assessment and conservation

“…CORT levels in southern leopard frogs increased with exposure to multiple aquatic stressors, specifically a nitrogenous fertilizer, a pesticide, and salt (Adelizzi et al, 2019). However, relatively elevated CORT levels were associated with populations less tolerant to contaminant exposure, such that differences in stress response could be indicative of exposure history (Shidemantle et al, 2022). Predator detection can also elicit an increased CORT response (Narayan et al, 2013).…”

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

“…1970) and aldosterone (hereafter, ALDO) have been prime candidates because of their roles in osmoregulation and counteracting stressors (McCormick & Bradshaw 2006; Shidemantle et al . 2021; Tornabene et al . 2021b).…”

“…In another study, adaptive tolerance influenced CORT responses for 3 different populations of wood frogs exposed to salinity (Shidemantle et al . 2021). CORT also mediated sublethal effects of salinity and a growth‐survival tradeoff for northern leopard frog larvae [ Lithobates pipiens (Schreber, 1782)]; survival was lower, but sublethal effects were mitigated when actions of CORT were suppressed (Tornabene et al .…”