A functioning immune system is important for survival in parasite-filled natural environments. Yet there is marked variation in both how individuals' immune systems respond to a challenge and in how well individuals cope with disease and physiological damage. Why does this variation exist? Immunological research in laboratory rodents suggests genetics play an important role. But we do not know to what extent genes and environmental conditions influence immunity under complex natural conditions, in which individuals are exposed to diverse and variable parasite challenges. Just as importantly, we still need to establish how variation in immune measures at a cellular level scale up to influence organism-level function, parasite resistance, and ultimately reproductive fitness.
We address these questions using the extraordinary long-term study of wild Soay sheep on St Kilda. The study has been running since 1985 and unique longitudinal information on individuals' behaviour, life history, parasite burdens and fitness - as well as blood and tissue samples - are available over several generations. We are currently working to understand the genetic and environmental drivers of variation in immune markers we can assay from blood samples collected in the field, including circulating antibody levels, inflammatory markers (acute phase proteins, cytokines) and T cell phenotypes and functional responses to ex vivo stimulation. Importantly, we are able to link variation in these immune markers to parasite burden, reproductive success and over-winter survival. Recently published work on circulating levels of antibodies reveals both heritable variation and counter-balancing positive associations with survival and negative associations with reproductive performance.
Recent publications:
Watt, K, Nussey, DH, Maclellan, R, Pilkington, JG, Pemberton, JM & McNeilly, TN (2016) Faecal antibody levels as a non-invasive method for measuring immunity to gastro-intestinal nematodes in ecological studies. Ecology & Evolution. On-line early. [Download here]
Nussey, D.H., Watt, K.A., Clark, A., Pilkington, J.G., Pemberton, J.M., Graham, A.L. & McNeilly, T.N. (2014) Multivariate immune defences and fitness in the wild: Complex but ecologically important associations among plasma antibodies, health and survival. Proceedings of the Royal Society B, 281: 20132931. [Download here]