Territory proximity influences aggression and modulates the relationship between social dominance and oxidative stress in a highly social African cichlid fish

High social rank has many benefits, including priority access to mates and resources. However, maintaining high rank or social dominance can be physiologically costly, particularly in species that engage in agonistic competition to maintain their dominance status. Previous studies have rarely manipulated the intensity of agonistic competition in controlled settings to isolate the cost of social dominance. We utilized males of the cichlid fish Astatotilapia burtoni to investigate how the degree of territoriality influences patterns of oxidative stress. In this species, high-rank males compete for territories to attract mates. We housed males individually with a defendable structure and used clear tank dividers to allow visual access to a size-matched male neighbor housed in an identical setup to manipulate territoriality. Defendable structures were placed either close to the divider (proximal treatment) or further away (distal treatment). We found that males in the distal treatment expressed higher levels of territorial aggression than those in the proximal treatment. While males in the distal treatment did not display higher levels of oxidative stress, territory proximity influenced the relationships between physiological markers of dominance (i.e., testosterone, gonad size) and oxidative balance. Although our work is not consistent with higher competition increasing the physiological cost of high rank, it suggests that the level of competition influences the regulation of oxidative balance relative to social dominance characteristics. We suggest that manipulating the degree of territoriality in a controlled setting provides a unique opportunity to further our understanding of how individuals manage the trade-offs associated with high rank. Summary StatementManipulating the amount of space between territories results in variability in the degree of territorial aggression and the interaction of physiological markers of social dominance and oxidative stress.