Search

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 towards 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

Summary 1Egg size is an important maternal trait that can have major consequences on offspring phenotype. However, the effects of the variation of different components of cleidoic eggs have been little investigated. 2Here, we addressed whether a reduction of the relative egg albumen content within the natural range of variation affects viability, time to hatching, early post-natal begging displays, morphology and immune response of yellow-legged gull Larus michahellis chicks. 3Egg mass strongly positively predicted chick size and mass at all ages, while time to hatching positively predicted tarsus length and immune response, irrespective of albumen removal. Variation in time to hatching may thus affect immune system maturation. 4Albumen removal resulted in a lower embryonic viability and increased time to hatching of individual eggs. The probability that an egg originated a chick surviving until 8 days of age increased with original egg mass among controls, but not among chicks hatching from eggs with reduced albumen content (‘albumen chicks’). 5Begging rate increased with laying order among albumen chicks while it decreased among controls. Concomitantly, begging rate decreased with egg mass among controls while it did not vary among albumen chicks. Surprisingly, albumen removal did not affect body mass or tarsus length except at 8 days of age, when control chicks were lighter than albumen chicks. 6In conclusion, our study indicates that a reduction of the relative egg albumen content can have complex effects on offspring development, behaviour and viability of a semiprecocial bird, suggesting that the relative albumen content of the eggs represents an important mechanism of maternal effects.