Fecal Glucocorticoid Response to Periodic Social Stress in Male Green Anoles, Anolis carolinensis

Abstract

Agonistic encounters necessary for territory establishment and maintenance can be stressful for those involved. Stress responsiveness associated with territorial behavior can occur on both acute and chronic temporal scales contingent upon social status. Social interactions that recur for territory maintenance pose periodic stressors that incur variable physiological costs across social ranks. Adult males of the Green Anole, Anolis carolinensis, experience stressful social encounters during territorial disputes as individuals contest status within a dominance hierarchy. Dominant males in stable territories are known to exhibit greener body coloration and lower levels of stress hormone, corticosterone, relative to their subordinate counterparts. Periodic interactions with novel competitors, however, may induce comparable levels of cumulative glucocorticoid secretion regardless of social status. Glucocorticoid metabolites excreted in feces can be quantified to assess the chronic hypothalamic–pituitary–adrenal (HPA) axis response to periodic social stressors. Fecal glucocorticoid metabolite (FGM) levels in male A. carolinensis were hypothesized to increase in response to novel social encounters that simulated territory establishment and maintenance. Adrenocortical response to recurring episodes of territoriality was predicted to generate similar longitudinal FGM levels across social ranks. FGM analysis was combined with behavioral assessment of body coloration to further contextualize measured stress levels of dominant and subordinate anoles. Prolonged social interaction led to similarly increased levels of fecal glucocorticoid metabolites in both dominant and subordinate anoles relative to those that were solitary. This study provides an alternative perspective on the activity of the HPA axis in dominant–subordinate relationships of A. carolinensis over prolonged periods of territoriality.