Oxidative status in nestlings of three small passerine species exposed to metal pollution.

Antioxidant defense has an important role in the protection of organisms against oxidative stress caused by reactive oxygen species (ROS). Many metals are capable of generating ROS and inducing oxidative damage, and may therefore lead to changes in oxidative regulation. We studied species-specific variation in the oxidative status of great tit (Parus major), blue tit (Cyanistes caeruleus) and pied flycatcher (Ficedula hypoleuca) nestlings in a vicinity of a non-ferrous smelter. Non-enzymatic (glutathione [tGSH], GSH:GSSG ratio, and carotenoids) and enzymatic (glutathione peroxidase [GP], glutathione-S-transferase [GST], superoxide dismutase [SOD], and catalase [CAT]) antioxidants were evaluated to determine the effects of metal exposure on the oxidative status of the birds. We found strong evidence of interspecific variation in CAT and SOD activities, whereas less variation was observed in parameters related to glutathione metabolism. Oxidative state (in terms of tGSH and GSH:GSSG) did not vary between species, suggesting that different species may employ different antioxidant pathways to achieve the same oxidative state. Oxidative status was only weakly related to metal exposure, and these associations were further obscured by species-specific environmental effects. Our results indicate that effects on oxidative status observed in one species cannot be generalized to other ones. Future work should attempt to incorporate species-specific biology and environmental context into assessments of contaminant impacts on oxidative regulation of passerine birds.