Janske van de Crommenacker, Martijn Hammers, Jildou van der Woude, Marina Louter, Peter Santema, David S. Richardson and Jan Komdeur

An important ecophysiological trade-off is oxidative stress: the balance between damaging pro-oxidants (oxidative damage) generated during metabolic processes, and the antioxidant barrier, a series of compounds that inhibits the detrimental oxidation of biological macromolecules. When this balance is skewed towards pro-oxidants, a state of oxidative stress occurs that might result in early ageing and advanced death. As resource allocation towards anti-oxidant protection likely comes with costs elsewhere (growth, immune function, reproduction), oxidative stress may affect fitness via different routes. Yet, the results of studies that have investigated fitness consequences of oxidative status are rather inconclusive.

Here we investigate how oxidative damage and antioxidant capacity are linked with survival and reproductive output in a wild population of Seychelles warblers (Acrocephalus sechellensis) on Cousin Island, Seychelles. We found that higher antioxidant capacity resulted in a lower probability of surviving until the next year. This matched the results of an extensive study across North-American bird species, which emphasized the importance of the pace of life: “live fast, die young” versus “live slow, die old”. The tropical Seychelles warbler falls within the second group, with basal antioxidant levels likely to be low due to their constant environment, and elevated levels that may only directly respond to higher levels of pro-oxidants produced in challenging situations. These antioxidant elevations may be traded off with reduced resource allocation into other traits, e.g., immunocompetence, thereby increasing short-term mortality.

Unlike for survival, there was no significant association between oxidative parameters and reproductive output. Individuals may successfully manage to counteract oxidative challenges so that their reproductive output is not impaired, but at the expense of lowered survival.

Care should be taken while interpreting our non-experimental results, but as it is challenging to collect physiological data in a free-living species and combine these with long-term fitness information, our study provides a valuable contribution to the attempt to better understand the role of the oxidative balance in shaping life-history trade-offs.

Image caption: Photo provided by authors.
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