Natural selection on a measure of parasite resistance varies across ages and environmental conditions in a wild mammal.

摘要: Parasites detrimentally affect host fitness, leading to expectations of positive selection on parasite resistance. However, as immunity is costly, fitness may be maximized at low, but nonzero, infection intensities. These hypotheses are rarely tested natural variation in free-living populations. We investigated a measure resistance naturally regulated Soay sheep population using longitudinal data set and found negative correlations between intensity annual lambs, male yearlings adult females. having accounted for confounding effects body weight, the effect was only significant lambs. Associations were environment-dependent, being strong during low-mortality winters, negligible harsher high-mortality winters. There no evidence stabilizing selection. Our findings reveal processes that shape populations illustrate importance accounting correlated traits analysis.