Costs and constraints of cellular immune activity during development in an arboreal primate.

Evolutionary life history theory predicts that, during development, investment in immunity must be balanced with the demands of growth. How, and at what time scales, this balance is negotiated is unclear. In this study, we examined the potential energetic costs and limitations to cellular immune activity during development, its trade-offs with growth, related sickness behaviour and the role of hypothalamic-pituitary-adrenal (HPA) axis activity in these relationships. We combined biomarker and socio-environmental data on wild juvenile blue monkeys collected over eight months. Rather than detract from energy balance (C-peptide) and growth of lean body mass (creatinine by specific gravity residuals), cellular immune activity (neopterin) increased with energy balance and lean body mass at monthly time scales, suggesting an energetic constraint on cellular immunity. At shorter time scales, higher neopterin diminished subsequent growth. Energetic constraints on immune activity were weakly regulated by HPA activity during low energy states. Our results suggest that cellular immune activity is both costly and limited by physical condition in wild developing primates.