Out of the shed and into the field: an immune toolkit for measuring wild ungulate immune phenotypes at multiple scales

Introduction Understanding factors that shape immune responses in wild animals is critical to predicting population resilience and long-term persistence. Immune function modifies the survival of individuals facing infectious disease, trauma, and environmental stressors, yet remains understudied. An individual’s immune response is shaped not only by current and historic pathogen exposures but is mediated by both individual (e.g. host genetics, metabolic plane, age, and sex) and population-level (e.g. population size, density, and connectivity) factors. Bighorn sheep (Ovis canadensis, bighorn) occupy populations of varying sizes, nested within larger metapopulations, creating a hierarchical structure. This organization provides a useful framework to understand how immune parameters vary across individual, population, and metapopulation levels. Unfortunately, measurement of immune parameters in ungulates is limited. Methods To address this limitation, we measured 18 immunologic traits across 581 wild bighorn to evaluate this toolkit’s ability to detect immunological differences between individuals, populations, and metapopulations. Results Most immunological phenotypes illustrated significant variation at the metapopulation level and individual level. Our assays revealed immune phenotypic variation consistent with two main axes of segregation—one that distinguished tradeoffs in bighorn innate versus adaptive immune responses, and another reflecting alternative inflammatory states, defined by distinct cytokine patterns. Bighorn age and sex also mediated immune response patterns. Conclusions Our immunological toolkit sets the stage to further clarify landscape-level immunological variation in wild ungulate populations and provides a template for deploying integrative eco-immunological tools in any natural population to further understand wildlife health.