Experimental evidence that social instability influences rank-specific patterns in 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, ROM) compared to subordinate males in stable hierarchies only. Subordinate males in unstable hierarchies had higher ROM than their stable community counterparts, but we found no effect of social stability treatment for dominant males. However, dominant males tended to have lower liver total antioxidant capacity (TAC) than subordinate males in unstable hierarchies, suggesting that the cost of social dominance is higher in unstable hierarchies. There was no other effect of status in tissue (liver, gonad, muscle) or various redox markers including TAC and 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.