Hidden but Potentially Stressed: A Non-Invasive Technique to Quantify Fecal Glucocorticoid Levels in a Fossorial Amphisbaenian Reptile

SIMPLE SUMMARY: Soil alterations may negatively affect the health of animals living inside these soils, but these negative effects are often unexplored and remain “hidden” underground. This study examines the validity of a non-invasive technique to quantify glucocorticoid levels of the amphisbaenian Trogonophis wiegmanni, a fossorial burrowing reptile. Quantification of corticosterone metabolites was made from fresh fecal samples using an enzyme immunoassay kit. An experimental external supplementation of corticosterone to a group of amphisbaenians was detected in their feces as an increase in their fecal glucocorticoid metabolite levels, confirming that this treatment can be used to induce physiological increases of this hormone in these animals. We also quantified baseline fecal glucocorticoid metabolite levels in a field population of this amphisbaenian using this technique. Results showed that although there were no differences between sexes, sizes, or seasons, there was a high interindividual variation, which may allow using this measurement and technique to examine in detail the environmental causes that may produce this variation. ABSTRACT: To understand wildlife responses to the changing environment, it is useful to examine their physiological responses and particularly their endocrine status. Here, we validated an enzyme immunoassay (EIA) to non-invasively quantify fecal corticosterone metabolites (FCM) in the fossorial amphisbaenian reptile Trogonophis wiegmanni from North Africa. We supplemented animals assigned to the treatment group with corticosterone dissolved in oil applied non-invasively on the skin for several days, while control groups received the oil-alone solution. Fresh feces were collected at the end of the supplementation period, and FCM levels were quantified by an EIA. Basal FCM levels were similar for both treatments and increased at the end of the test, but FCM increased significantly more in corticosterone-treated animals. A further examination of FCM levels in a wild population of this amphisbaenian did not find overall sexual, size or seasonal differences but showed a high range of variation among individuals. This suggests that different uncontrolled intrinsic or local environmental variables might increase the circulating glucocorticoid levels of different individuals. Our results confirmed the suitability of EIA for analyzing physiological changes in FCM in this amphisbaenian species. This technique may be useful for understanding and remediating the little-explored potential stressors of the soil environment that may negatively affect the health state of fossorial reptiles.