What it takes to be at the top: The interrelationship between chronic social stress and social dominance

Dominance hierarchies of social animal groups are influenced by complex factors such as stress. Stress experienced by an animal prior to social interactions with a conspecific may be a determinant of their future social dynamics. Additionally, long-term occupancy of a specific hierarchical rank can have psychophysiological effects, leading to vulnerability to future stress. The current study aimed to delineate differential effects of stress acting before or after hierarchy formation. Using the chronic social defeat stress (CSDS) paradigm we performed behavioural investigations to determine whether exposure to CSDS before hierarchy formation predicted the new dominance status. Moreover, in another study we investigated whether social rank predicted stress vulnerability. We found that CSDS did not impede the establishment of dominance in new hierarchies as both stress-susceptible (socially avoidant) and –resilient (social) mice were able to attain dominant ranks. In contrast, within newly established hierarchies of stress-naïve mice, the subordinate, but not dominant, mice exhibit significantly greater avoidance of novel social targets. However, following exposure to CSDS, both lowest- and highest-ranked mice exhibit strong susceptibility to stress as measured by decreased interactions with a novel social target. These results suggest that the response to chronic social stress did not determine social rank in new cohorts, but low-status mice in newly established groups exhibited lower sociability to novel social targets. Interestingly, exposure of a hierarchical social group to chronic social stress led to stress-susceptibility in both high- and low-status mice as measured by social interaction. Highlights Stress susceptibility to chronic social defeat did not impede the establishment of dominance in new hierarchies. Subordinate mice exhibit reduced social preference after hierarchy formation. Following chronic social defeat stress, both subordinate and dominant mice exhibit susceptible-like reduction in social interaction, but dominant mice exhibit the greater decrease in social preference as compared to baseline.