Chernobyl’s Radiation Turned Its Local Frogs Black -

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Chernobyl’s Radiation Turned Its Local Frogs Black

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It’s not often that you can watch evolution in action right in front of your eyes, but if you ever manage to visit the Chernobyl Exclusion Zone — which is a most unusual holiday plan — then you may notice its normally green frogs are now black. As black as charcoal briquettes. What happened?
In April 1986, Chernobyl was the scene of a major nuclear reactor disaster that released the largest amount of nuclear radiation into the environment in history. This accident resulted in huge amounts of radioactive cesium-137 being deposited throughout most of Ukraine as well as in parts of Norway and the UK. The human population was evacuated, and the area was designated a wildlife reserve — the largest in Europe.
The local wildlife remained on site, and now, 36 years later, these animals are providing scientists from around the world with the unique opportunity to study whether and how they are adapting to living with high levels of radiation.
It is well-known that radioisotopes that collide with DNA can damage it, and this damage can create to genetic mutations. These mutations can lead to cancers, malformed offspring, death, or it can create mutations that can be passed to the next generation.
But not all genetic mutations are harmful. Apparently, some of these genetic mutations caused the local population of the Eastern tree frog, Hyla orientalis, to change its skin color from bright green to black.
“Tree frogs living within the Chernobyl Exclusion Zone had a remarkably darker dorsal skin coloration than frogs from outside the Zone”, the authors, Pablo Burraco and Germán Orizaola, noted in their recent research paper (ref).
But why did these frogs’ skin turn black?
Black skin color is created by a group of pigments known as melanins. The quantity of melanins present in skin and hair creates darker colors for many animals, including humans. Melanins are important for reducing the harmful effects of ultraviolet radiation in sunshine — which is the reason that people develop a tan when exposed to a lot of sun. Melanins also protect DNA from the damaging effects of ionizing radiation from nuclear disasters by absorbing and dissipating at least some of the radiation’s damaging energy.
“Dark coloration is known to protect against different sources of radiation by neutralizing free radicals and reducing DNA damage, and, particularly melanin pigmentation has been proposed as a buffering mechanism against ionizing radiation”, the authors state in their recent research paper (ref).
According to this recent study, black skin may actually have been the result of an adaptive response to protect the frogs from tissue, cell and DNA damages and thereby increase their chances of survival. Correspondingly, the researchers found that frogs with the blackest skin were closest to the blast zone when the accident occurred and where radiation contamination was highest.
The authors point out that black coloration is not related to the levels of radiation contamination that the frogs experience today and that can now be measured in all individuals. Instead, the dark coloration is typical of frogs from within or near the most contaminated areas at the time of the accident.
“Skin coloration was darker in localities closest to areas with high radiation levels at the time of the accident, whereas current radiation levels seemed not to influence skin coloration in Chernobyl tree frogs”, the authors write in their recent research paper (ref).
This dark coloration may not be the result of genetic mutations caused by radiation contamination but instead, it may be due to frogs that had darker skin coloration at the time of the accident — which normally are a minority within their populations — surviving longer due to the protective effects of melanins. Of course, frogs that survive longest are also most likely to reproduce and pass on their beneficial adaptations to their offspring. More than ten frog generations have lived and died since the accident, suggesting that a very fast process of natural selection — radiation killing green frogs — may explain why dark frogs are now the predominant type within the Chernobyl Exclusion Zone.

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