Non-Invasive Assessment of Adrenal Activity in the Subterranean Rodent Ctenomys talarum in Field and Laboratory Conditions

The endocrine stress response is a valuable tool for evaluating how organisms cope with environmental challenges. However, selecting an appropriate matrix for measuring glucocorticoids (GCs) requires careful consideration of sample quality and accessibility. This study reveals that blood sampling affects plasma cortisol levels in the subterranean rodent <i>Ctenomys talarum</i>, with the effect being reversed shortly thereafter. To facilitate a non-invasive approach, an enzyme-linked immunosorbent assay (EIA) that had previously been validated for measuring plasma cortisol in <i>C. talarum</i> was evaluated to measure adrenocortical activity by analyzing fecal glucocorticoid metabolites (FGCs). Using this assay, we monitored the stress response during wild capture, transport to captivity, adrenocorticotropic hormone (ACTH) stimulation, and immobilization. This showed that FGC levels accurately reflect adrenal activation in these contexts. We also documented a relationship between reproductive seasonality and FGCs. Finally, we provide evidence for a relationship between adrenal activity and behavior. Our results suggest that when considering plasma GCs for the assessment of acute stress, it is crucial to understand the magnitude and timing of the effects of blood sampling on the stress state of organisms. The validation of FGC measurement in <i>C. talarum</i> provides a new option for advancing ecophysiological studies in both the wild and captivity.