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.