Ecologically similar marine species inhabiting the same areas compete for food resources. Such competition is reduced by resource-partitioning strategies that may affect physiology. For instance, diet and feeding strategies may affect the antioxidant defences or the production of reactive oxygen species. Oxidative stress is defined as the imbalance between pro-oxidants and antioxidant defences. If such an imbalance favours the former, this can lead to oxidative damage, and oxidative stress increases. However, to our knowledge, how free-ranging animals adjust their oxidative status in relation to their foraging habitats, diet and dietary antioxidants has not yet been studied. Penguins are an interesting biological model for such a comparison because their diet, based on krill, fish and/or cephalopods, presents strong variation in dietary antioxidant content. We therefore examined trophic level (δ15N), foraging habitat (δ13C), dietary antioxidants (retinol, α-tocopherol and astaxanthin) and oxidative status (plasma non-enzymatic antioxidant capacity and oxidative damage) in pygoscelid penguins (chinstrap Pygoscelis antarcticus, gentoo P. papua and Adélie P. adeliae) breeding in Antarctica. We found interspecific differences in all variables analysed except α-tocopherol. Gentoo penguins exploited more cephalopods and fish in coastal and benthic habitats, Adélies showed an intermediate position, whereas chinstraps foraged more on krill and fish in pelagic waters. Dietary antioxidant levels showed specific patterns resulting in relationships with prey items. However, we did not find any clear relationships between dietary antioxidants and species-specific antioxidant capacity, suggesting the importance of endogenously produced antioxidants. Oxidative status appeared to be differently related to foraging strategy and antioxidant capacity in each species.
