Life history correlates of oxidative damage in a free-living mammal population

P>Reactive oxygen species, produced as a by-product of normal metabolism, can cause intracellular damage and negatively impact on cell function. Such oxidative damage has been proposed as an evolutionarily important cost of growth and reproduction and as a mechanistic explanation for organismal senescence, although few tests of these ideas have occurred outside the laboratory. Here, we examined correlations between a measure of phospholipid oxidative damage in plasma samples and age, growth rates, parasite burden and investment in reproduction in a population of wild Soay sheep on St. Kilda, Scotland. We found that, amongst females of different ages, lambs had significantly elevated levels of oxidative damage compared to all other age classes and there was no evidence of increasing damage with age amongst adult sheep. Amongst lambs, levels of oxidative damage increased significantly with increasing growth rates over the first 4 months of life. Neither mean damage nor the effect of growth rate on damage differed between male and female lambs. Amongst adult female sheep, there was no evidence that body mass, current parasite burden or metrics of recent and past reproductive effort significantly predicted oxidative damage levels. This study is the first to examine age variation in an assay of oxidative damage and correlations between oxidative damage, growth and reproduction in a wild mammal. Our results suggest strong links between early conditions and oxidative damage in lambs, but also serve to highlight the limitations of cross-sectional data for studies examining associations between oxidative stress, ageing and life history in free-living populations.