9.4 Wednesday, Jan. 4 Rank-related variation in immune function in a gregarious carnivore FLIES, Andrew S*; MANSFIELD, Linda S; TSAO, Jean I; HOLEKAMP, Kay E; Michigan State University; Michigan State University; Michigan State University; Michigan State University email@example.com
Immune defenses are energetically costly in many ways, including nutritional demands of producing new immune defense cells and molecules, and collateral damage to unintended targets of immune defenses. A growing body of evidence supports the hypothesis that resource quality can affect immune function by reducing trade-offs among competing physiological functions. Here we tested the hypothesis that differential access to food resources would affect immune function among spotted hyenas (Crocuta crocuta). Spotted hyenas live in social groups containing up to 90 individuals; priority of access to food by individual group members is determined by their positions in a strict linear dominance hierarchy. Males disperse from their natal territories but females are philopatric and their offspring assume ranks immediately below them in the group’s hierarchy; immigrant males are subordinate to all females. High-ranking hyenas are able to monopolize carcasses of prey animals, and feed until they are satiated, whereas subordinate group members generally obtain lesser quality and quantity of food. The top priority of access to resources enjoyed by high-ranking hyenas results in fitness benefits mediated by faster growth, earlier onset of breeding, and shorter inter-litter intervals. We predicted that superior food access would enhance immune defenses among high-ranking female spotted hyenas. We used serum from wild hyenas in bacterial killing assays to assess one aspect of immune function. Initial analyses showed that sera from high-ranking females had greater bacterial killing ability than sera from low-ranking females. We also inquired whether total immunoglobulins and white blood cells similarly vary with social rank.