Data from: Age, oxidative stress exposure and fitness in a long-lived seabird

The need to manage exposure to oxidative stress, which can damage macromolecules, is thought to influence the resolution of life history trade-offs. Oxidative damage is expected to increase with age as a consequence of changes in the optimal investment in defences or repair, and/or because of senescence in antioxidant defence systems, though the pattern might differ between short and long-lived species. However, data on age related changes in damage levels in wild populations are rare. Using cross-sectional and longitudinal data collected over three years, we examine variation in a measure of oxidative damage exposure in known age, wild European Shags (Phalacrocorax aristotelis), a relatively long lived species. The cross-sectional data showed a quadratic relationship between oxidative damage exposure and age: both relatively young and old adults had higher levels than those in middle age. In contrast, a measure of non-enzymatic antioxidant levels did not vary with age. The cross-sectional increase in oxidative damage exposure in later life was consistent with longitudinal patterns observed within older birds (more than 10 years old). However, the apparent decline in oxidative damage in early adulthood was not consistent with longitudinal patterns in younger birds, which showed individual variation but no consistent age-related change in the marker. This suggests that cross-sectional patterns reflect instead higher disappearance of individuals with high exposure to oxidative damage at this life stage. Our data further show that oxidative damage levels are predictive of attendance at the colony in all age classes: juveniles fledging with a high damage exposure index were less likely to be resighted in the breeding colony two years later, and adults with high levels at the end of the breeding season had reduced return rates, irrespective of age. Since this is a species that shows high colony fidelity, this is likely to reflect mortality patterns. These data suggest that exposure to oxidative damage increases with age in a long lived species, but only in later life, when high investment in reproduction at the cost of defence would be predicted.

机体对可造成大分子（macromolecules）损伤的氧化应激（oxidative stress）暴露进行管控的需求，被认为会影响生活史权衡（life history trade-offs）的解决过程。氧化损伤（oxidative damage）水平随年龄增长而升高，这一现象被认为源于防御或修复的最优投资变化，或是抗氧化防御系统的衰老所致，不过短寿与长寿物种间的模式可能存在差异。然而，野生种群中与年龄相关的损伤水平变化数据十分匮乏。本研究借助历时三年收集的横断面数据（cross-sectional data）与纵向数据（longitudinal data），对已知年龄的野生欧洲鸬鹚（Phalacrocorax aristotelis）——一种寿命较长的物种——的氧化损伤暴露指标的变异情况展开分析。横断面数据显示，氧化损伤暴露与年龄呈二次函数关系：相对年轻与年老的成年个体，其氧化损伤水平均高于中年个体。与之相对，非酶抗氧化剂（non-enzymatic antioxidant）水平的检测指标并未随年龄发生显著变化。晚年氧化损伤暴露的横断面升高趋势，与10龄以上老龄个体的纵向观测模式一致。不过，成年早期氧化损伤的表观下降趋势，与幼龄个体的纵向模式并不相符——幼龄个体虽存在个体差异，但该检测指标未出现明确的年龄相关变化。这表明横断面模式实则反映了该生命阶段中，氧化损伤暴露水平较高的个体出现更高的消失率。本研究数据还显示，氧化损伤水平可预测各年龄组个体在繁殖群落的出勤情况：氧化损伤暴露指数较高的离巢幼鸟，两年后在繁殖群落中被再次观测到的概率更低；而繁殖季末期氧化损伤水平较高的成年个体，无论年龄如何，其回归率均有所降低。由于该物种具有较高的群落忠实性（colony fidelity），这一结果很可能反映了死亡率模式。上述数据表明，在长寿物种中，氧化损伤暴露水平随年龄增长而升高，但仅出现在晚年——此时个体以抗氧化防御为代价高投入繁殖，符合理论预测。