Validation of a Method for Measuring the Fecal Glucocorticoid Metabolites in the Midday Gerbil (Meriones meridianus Pallas 1773, Muridae, Rodentia): Biological and Physiological Approaches

Estimating the level of stress in wild populations opens opportunities for studying various populational processes, including population dynamics, range expansions, and colonization. Over the past two decades, methods for a noninvasive assay of the glucocorticoid levels have been actively developed and widely implemented in various biological fields. They are most suitable for assessing long-term stress, but require a validation procedure for each new animal species studied. We have conducted biological and physiological validation of a noninvasive method for determination of fecal glucocorticoid metabolites (FGMs) in the midday gerbil, Meriones meridianus. Both methods showed a significant increase in the concentration of FGMs after a similar time after manipulations (4–5 hours after stressful procedures or the administration of ACTH), and peak values were two times the baseline. Saline injection (control group) did not cause a significant increase in the FGM concentration, thus confirming that the noninvasive measuring of a smoothed level of FGMs is more suitable for assessing the long-term stress, in contrast to the assay of glucocorticoids in the blood. The biological validation was as effective as the physiological method, which is commonly considered more reliable. Given the low invasiveness of the biological method, the high effectiveness expands the potential for its application.