Social instability influences rank-specific patterns of oxidative stress in a cichlid fish

In many animal societies, dominant individuals have priority access to resources. However, defending high rank can be costly, especially in unstable social hierarchies where there is more intense competition. Oxidative stress has been proposed as a potential cost of social dominance, but few studies have examined this cost in relation to social stability. We studied the cost of social dominance in the cichlid fish Astatotilapia burtoni by manipulating social stability among males in replicate naturalistic communities for 22 weeks. We found that our social stability treatment influenced status-specific patterns in 3 out of 6 measurements of oxidative stress. Specifically, dominant males experienced increased plasma oxidative damage (measured as reactive oxygen metabolites, ROMs) compared with subordinate males in stable hierarchies only. Subordinate males in unstable hierarchies had higher ROMs than their stable community counterparts, but we found no effect of social stability treatment for dominant males. However, dominant males tended to have reduced total antioxidant capacity (TAC) in the liver when compared with subordinate males in unstable hierarchies, suggesting that the cost of social dominance is higher in unstable hierarchies. There were no effects of status and treatment on gonad TAC, muscle TAC or oxidative DNA damage. We conclude that the stability of the social environment influences the relative cost of social dominance in a tissue- and marker-specific manner.