Fecal hormone variation during prolonged social interaction in male Tscheskia triton

Agonistic behavior is crucial for conspecific members to maintain a social hierarchy, optimum population density, and high fitness. It is known that agonistic behavior and social ranking often interact with hormones such as testosterone (T) and glucocorticoids (GCs). The challenge hypothesis states that T levels in males are promoted by the agonistic behaviors of other males and has been widely testified in many taxa of vertebrates, even in humans, but seldom attempted in rodents. Here, we examined how fecal T and corticosterone (CORT) concentrations changed during prolonged social conflict in male greater long-tailed hamsters (Tscheskia triton). Dyads were subjected to 5 min staged encounters daily for 15 days during which agonistic and social behaviors were recorded and fecal hormone concentrations were determined by radioimmunoassay. Our results showed that pairwise male hamsters developed overt and stable dominant-subordinate relationships rapidly and that the agonistic behavior decreased over the course of the experiment. Dominant males exhibited more frequent flank marking and locomotion and shorter latency to initial attack than their subordinate counterparts. Testosterone levels were significantly increased in both dominant and subordinate males during early encounters, but T and CORT levels were higher in subordinate males. After five encounters, we found no difference between hormone levels and behavior for all males, implying some kind of behavioral and physiological habituation. This complex pattern of hormonal change during social conflict is discussed and correlations between behavioral and physiological habituation are hypothesized.