Heterogeneity in Mucosal Immunity of Wild Savannah Baboons, Papio cynocephalus

Abstract

Infection by parasites is costly to host fitness and a functional immune system is essential to mitigating those costs. However, the limit on energetic resources puts a cap on the strength of response a host can mount. Using wild savannah baboons in Amboseli National Park in Southern Kenya as my study population, I investigated the extent to which, in the face of these constraints, we see trade-off relationships between host investment in immune responses to parasites in the gut, where a food-borne pathogens are pervasive, and life history traits such as dominance rank and age class. Immunoglobulin (Ig) A was selected as an indicator of mucosal immune status because it is the dominant antibody class in the gut and is present in large quantities in feces, allowing for large-scale noninvasive fecal sampling of wild animals. I validated a method for quantifying IgA in baboon feces and compared those total IgA levels to life history information from a longitudinal dataset made available by the Amboseli Baboon Project. For male baboons, total IgA was found to depend on the combination of an individual’s age, dominance rank, and testosterone level. Higher-ranking individuals in early adulthood with higher testosterone concentrations mounted the most robust immune responses in the gut. The relevance of these traits to host health were not surprising considering that quality of life varies dramatically with dominance rank and that the relative importance of reproductive effort depends on age. For females, we did not identify any significant predictors of immune phenotype, underscoring the extent to which the significance of life history traits on host fitness varies between the sexes. My results highlight the extent to which host immune heterogeneity exists in a wild system and have allowed me to draw some initial conclusions about the explanatory power of various traits for that heterogeneity in a social primate.