Effects of isolation-rearing on the development of social behaviors in male Mongolian gerbils (Meriones unguiculatus).

Social isolation has been shown to modify behavioral patterns and neuroendocrine function in many species. In this study, we examined the influence of post-weaning social isolation on the behavioral development and fecal testosterone and corticosterone levels of male Mongolian gerbils. In Experiment 1, isolation-reared (IR) males spent more time engaged in social-sniffing. IR males also showed more aggressive and anxiety-related behaviors than group-reared males (GR; three animals per cage). In Experiment 2, a screen-divided-reared condition (SDR) was examined in addition to GR (two males per cage) and IR males. In the SDR group, two subjects were separated by a wire mesh screen allowing for sensory communication and limited physical contact but not direct social interactions. SDR males showed similar patterns in sniffing and anxiety-related behaviors to IR males; however, an increase in aggression was not observed. No differences in fecal testosterone and corticosterone levels were found among males in different rearing conditions. These results suggest that post-weaning social isolation affects behavioral development without affecting testosterone and corticosterone levels. The behavioral changes observed may therefore be regulated by different mechanisms; increases in social-sniffing and anxiety-related behaviors may be caused by the deprivation of direct social interactions, whereas the enhancement of aggressive behaviors may be caused by the lack of sensory stimulation and limited physical contact with other individuals.