Data from: Chronic exposure to low-dose radiation at Chernobyl favours adaptation to oxidative stress in birds

1. Ionizing radiation produces oxidative stress, but organisms can adapt
to their exposure with physiological adaptive responses. However, the role
of radioadaptive responses in wild populations remains poorly known. 2. At
Chernobyl, studies of birds and other taxa including humans show that
chronic exposure to radiation depletes antioxidants and increases
oxidative damage. Here we present analyses of levels of the most important
intracellular antioxidant (i.e., glutathione, GSH), its redox status, DNA
damage and body condition in 16 species of birds exposed to radiation at
Chernobyl. We use an approach that allows considering the individual bird
as the sampling unit while controlling for phylogenetic effects, thus
increasing the statistical power by avoiding the use of species means as
done for most previous comparative studies. 3. As a consequence, we found
a pattern radically different from previous studies in wild populations,
showing that GSH levels and body condition increased, and oxidative stress
and DNA damage decreased, with increasing background radiation. Thus, when
several species are considered, the overall pattern indicates that birds
are not negatively affected by chronic exposure to radiation and may even
obtain beneficial hormetic effects following an adaptive response.
Analysis of the phylogenetic signal supports the existence of adaptation
in the studied traits, particularly in GSH levels and DNA damage. 4. We
also show that, under equal levels of radiation, the birds that produce
larger amounts of the pigment pheomelanin and lower amounts of eumelanin
pay a cost in terms of decreased GSH levels, increased oxidative stress
and DNA damage, and poorer body condition. Radiation, however, diminished
another potential cost of pheomelanin, namely its tendency to produce free
radicals when exposed to radiation, because it induced a change toward the
production of less pro-oxidant forms of pheomelanin with higher
benzothiazole-to-benzothiazine ratios, which may have facilitated the
acclimation of birds to radiation exposure. 5. Our findings represent the
first evidence of adaptation to ionizing radiation in wild animals, and
confirm that pheomelanin synthesis represents an evolutionary constraint
under stressful environmental conditions because it requires GSH
consumption.