Noninvasive measures of physiological stress are confounded by exposure

Diana J. R. Lafferty,Lindsay Clontz,Klaus Hackländer,L. Scott Mills,Marketa Zimova

doi:10.1038/s41598-019-55715-5

Abstract

Glucocorticoids and glucocorticoid metabolites are increasingly used to index physiological stress in wildlife. Although feces is often abundant and can be collected noninvasively, exposure to biotic and abiotic elements may influence fecal glucocorticoid metabolite (FGM) concentrations, leading to inaccurate conclusions regarding wildlife physiological stress. Using captive snowshoe hares (Lepus americanus) and simulated environmental conditions, we evaluated how different realistic field conditions and temporal sampling constraints might influence FGM concentrations using an 11-oxoetiocholanolone-enzyme immunoassay. We quantified how fecal pellet age (i.e., 0–6 days), variable summer temperatures, and precipitation affected FGM concentrations. Fecal pellet age had a strong effect on FGM concentrations (βAge = 0.395, s.d. = 0.085; β2Age = −0.061, s.d. = 0.012), which were lowest at the beginning and end of our exposure period (e.g., meanday6 = 37.7 ng/mg) and typically highest in the middle (meanday3 = 51.8 ng/mg). The effect of fecal pellet age on FGM concentrations varied across treatments with warm-dry and cool-wet conditions resulting in more variable FGM concentrations relative to control samples. Given the confounding effects of exposure and environmental conditions, if fresh fecal pellet collection is not an option, we encourage researchers to develop a temporally consistent sampling protocol to ensure all samples are exposed to similar environmental conditions.

Highlights

Glucocorticoids and glucocorticoid metabolites are increasingly used to index physiological stress in wildlife
We found that the age of feces affects fecal glucocorticoid metabolites (FGM) concentrations, and the age-FGM relationship has a curvilinear shape
We found multiple significant differences between the FGM concentrations in the control samples and FGM concentrations exposed to the environmental treatments (Fig. 1)

Summary

Introduction

Glucocorticoids and glucocorticoid metabolites are increasingly used to index physiological stress in wildlife. Using captive snowshoe hares (Lepus americanus) and simulated environmental conditions, we evaluated how different realistic field conditions and temporal sampling constraints might influence FGM concentrations using an 11-oxoetiocholanolone-enzyme immunoassay. The effect of fecal pellet age on FGM concentrations varied across treatments with warm-dry and cool-wet conditions resulting in more variable FGM concentrations relative to control samples. The confounding effects of exposure time and abiotic environmental conditions are variable by species and in some situations mitigated by observing animals and collecting samples immediately after defecation[20,21] or possibly by sampling feces deposited in snow[22]. We evaluated at what fecal pellet age FGM levels begin to differ from FGM concentrations in control samples when exposed to different environmental treatments (precipitation and temperature combinations). We provide recommendations for field study design to ensure measures of FGM concentrations represent the physiological state of the target animal and/or populations

Methods

Results

Conclusion