Meeting Abstract
For species living in dominance hierarchies, social rank dictates access to resources and often contributes to reproductive success. To ensure survival, individuals constantly evaluate trade-offs between crucial biological systems, like the reproductive and immune systems, depending on their social rank and physiological state. Little is known about how social species balance interactions between immune system function and fluctuations in social status and reproductive fitness, particularly in fishes, the largest and most diverse group of vertebrates. Astatotilapia burtoni is ideally suited to address this question because males reversibly transition between dominant reproductively-active and subordinate reproductively-suppressed phenotypes depending on their social environment. Here, we tested the hypothesis that immune responses differ with male social rank and reproductive state. We injected males with phytohaemagglutinin (PHA), a lectin that stimulates localized inflammation, and quantified differences in the width of the caudal peduncle in response to injection. We demonstrate that subordinate males have a greater difference in the width of their caudal peduncles (pre- vs. post-injection) compared to dominant males, indicative of the recruitment of more leukocytes and a stronger immune response. Sectioned spleens also showed differences in the quantity of macrophage centers between PHA and vehicle-injected males. Using qPCR, we are also comparing expression levels of pro-inflammatory cytokines in spleen and kidney of immune-challenged dominant and subordinate males. Because little is known about how reproductive physiology influences immune responses in fishes, this research provides greater insight into how socially plastic animals balance these trade-offs, with important implications for other taxa that exist in dominance societies.
