Complexity in relationships between antioxidants and individual life-history parameters in a seabird and a songbird

Selection on physiological traits is thought to mediate the evolution of individual life-history parameters like reproduction, longevity, and the tradeoffs between them, but almost nothing is known about the relationships between physiological and life-history parameters in the wild. Antioxidants are strong candidates to correlate with life histories because they play a critical role in preventing free radical damage to macromolecules, and many types are involved in sexual signaling and embryo provisioning. Here for the first time we present data on associations between serum antioxidant measures (antioxidant capacity and concentrations of uric acid, vitamin E and carotenoids) and indices of reproductive rate and age in two bird species. After controlling for age, 36% of the variation in hatching rate in Leach's storm-petrels Oceanodroma leucorhoa was accounted for by a negative association with antioxidant capacity. Age was negatively associated with uric acid levels. Savannah sparrows Passerculus sandwichensis showed no association between antioxidant capacity and fledging rate, but serum beta-carotene levels were weakly positively associated with fledging rate. Because antioxidant levels are known to vary markedly within individuals over time, detection of associations between long-term measures of reproduction and instantaneous antioxidant levels suggests strong (though not necessarily causal) relationships. Relationships between antioxidants and life histories appeared to differ in sparrows and storm-petrels though, likely due to variation in diet, ecology, and life-history evolution in these distantly related species.