Data from: Natural selection on a measure of parasite resistance varies across ages and environmental conditions in a wild mammal
Hayward, Adam D. et al. (2011), Data from: Natural selection on a measure of parasite resistance varies across ages and environmental conditions in a wild mammal, Dryad, Dataset, https://doi.org/10.5061/dryad.0045q
Parasites detrimentally affect host fitness, leading to expectations of positive selection on host parasite resistance. However, since immunity is costly, host fitness may be maximized at low, but non-zero, parasite infection intensities. These hypotheses are rarely tested on natural variation in free-living populations. We investigated selection on a measure of host parasite resistance in a naturally-regulated Soay sheep population using a longitudinal data set, and found negative correlations between parasite infection intensity and annual fitness in lambs, male yearlings, and adult females. However, having accounted for confounding effects of body weight, the effect was only significant in lambs. Associations between fitness and parasite resistance were environment-dependent, being strong during low-mortality winters, but negligible during harsher high-mortality winters. There was no evidence for stabilising selection. Our findings reveal processes that may shape variation in parasite resistance in natural populations, and illustrate the importance of accounting for correlated traits in selection analysis.