Social stress decreases marking behavior independently of testosterone in Mongolian gerbils

Abstract

This study examined the endogenous androgen regulation of the marking behavior in Mongolian gerbils ( Meriones unguiculatus). In the first experiment, developmental changes of fecal testosterone levels, ventral gland growth, and the marking frequency of male gerbils were investigated. From 9 weeks of age, marking frequency increased with increases in fecal testosterone levels and ventral gland size. The ventral gland size and marking frequency were significantly correlated to the fecal testosterone level. In the second experiment, we hypothesized that reduction in the marking frequency of subordinate males after social confrontations was controlled by a decrease in the circulating testosterone level, and we followed changes in marking frequency, endocrine status, and ventral gland size after social confrontations in which two adult male gerbils established their social ranks by fighting. As expected, marking frequency and ventral gland size were significantly related to social rank, that is, marking frequency was higher among dominant gerbils and lower among subordinates. In addition, fecal corticosterone levels among subordinates were higher than those of dominant animals. However, neither the fecal and plasma testosterone levels, nor testis size, differed between dominant and subordinate gerbils. These results revealed that endogenous androgen played a role in regulating marking behavior and ventral gland size during the developmental stage and that the reductions in marking frequency and ventral gland size occurring in subordinate males after social confrontations were not directly regulated by androgen changes.