Nearly three decades since the disaster and it seems the birds living in the exclusion zone around Chernobyl are adapting to long-term radiation exposure. And some of them aren’t even just coping, they appear to be benefiting.
Ionizing radiation damages cells by producing reactive compounds called free radicals. The body protects itself using antioxidants, but if their levels are too low, then the radiation produces genetic damage and oxidative stress (when free radicals overwhelm the bodies defenses), leading to aging and death.
Previous studies of wildlife at Chernobyl showed that chronic radiation exposure depleted antioxidants and increased oxidative damage. “We found the opposite,” Ismael Galván of the Spanish National Research Council says in a news release.
Using mist nets, Galván and colleagues captured 152 birds from 16 different species at eight different sites inside or near the exclusion zone, an area that spans 30 kilometers in radius. Humans can’t live here, although the area has become somewhat of an accidental ecological experiment. (Pictured, mist nets strung along a pasture near the power plant.) The team measured the background radiation levels of each site -- these ranged from 0.02 to 92.90 micro Sieverts per hour.
They took feather and blood samples from each bird before releasing them. In the blood samples, they measured levels of the antioxidant glutathione, oxidative stress, and DNA damage. With the feathers, they measured levels of melanin pigments. Eumelanin (black and brown) and pheomelanin (red and pink) are types of melanin. Because the production of the latter uses up antioxidants, animals who produce the most pheomelanins are likely to be more susceptible to the effects of ionizing radiation. They just don’t have enough antioxidants left over to fend off the free radicals.
The results reveal that with increasing background radiation, the birds’ overall body condition and antioxidant levels increased, while oxidative stress and DNA damage decreased.
However, birds who produce larger amounts of pheomelanin and lower amounts of eumelanin pay a cost: poorer body condition, decreased glutathione, and increased oxidative stress and DNA damage. The two negatively affected birds -- the great tit (Parus major) and the barn swallow (Hirundo rustica) -- both produce large amounts of the pinkish pigment in their feathers.
Previous lab experiments have shown that, with prolonged exposure to low doses, humans and other animals can adapt to radiation. And that it increases resistance to larger, subsequent doses. This study shows the first evidence that animals in the wild can adapt to ionizing radiation.
Here’s the entire list of all 16 birds surveyed were: red-backed shrike, great tit, barn swallow, wood warbler, blackcap, whitethroat, barred warbler, tree pipit, chaffinch, hawfinch, mistle thrush, song thrush, blackbird, black redstart, robin, and thrush nightingale.
The work was published in Functional Ecology this week.
Image: T.A. Mousseau and A.P. Møller 2011 (top), T.A. Mousseau 2011 (middle)