Data from: Multivariate immune defences and fitness in the wild: complex but ecologically important associations among plasma antibodies, health and survival

Despite our rapidly advancing mechanistic understanding of vertebrate
immunity under controlled laboratory conditions, the links between
immunity, infection and fitness under natural conditions remain poorly
understood. Antibodies are central to acquired immune responses, and
antibody levels circulating in vivo reflect a composite of constitutive
and induced functional variants of diverse specificities (e.g. binding
antigens from prevalent parasites, self tissues or novel non-self
sources). Here, we measured plasma concentrations of 11 different antibody
types in adult females from an unmanaged population of Soay sheep on St
Kilda. Correlations among antibody measures were generally positive but
weak, and eight of the measures independently predicted body mass,
strongyle parasite egg count or survival over the subsequent winter. These
independent and, in some cases, antagonistic relationships point to
important multivariate immunological heterogeneities affecting organismal
health and fitness in natural systems. Notably, we identified a strong
positive association between anti-nematode immunoglobulin (Ig) G
antibodies in summer and subsequent over-winter survival, providing rare
evidence for a fitness benefit of helminth-specific immunity under natural
conditions. Our results highlight both the evolutionary and ecological
importance and the complex nature of the immune phenotype in the wild.