Social status and gene expression in wild baboons

Social status predicts fitness outcomes in social animals, motivating efforts to understand its physiological causes and consequences. We investigated the relationship between social status and immune gene expression in male and female wild baboons. Importantly, female status is determined by kinship, while male status is determined by fighting ability. We uncover pervasive status-gene expression associations in males, but not females. In contrast to previous findings in hierarchies that are not competitively determined, we find that high status males exhibit high levels of pro-inflammatory gene expression. Using Mendelian randomization, we show that this variation in immune gene expression precedes dominance rank attainment: males who compete successfully for high status are intrinsically immunologically distinct. The nature of social hierarchies thus fundamentally shapes the relationship between social status and immune function.