Chernobyl frogs ‘turned brown’

A study carried out since 2017 in the Chernobyl Exclusion Zone (Ukraine) by a group of Spanish researchers reveals that the frogs in that area they have a darker pigmentation than those of nearby areas. According to the authors, the dark coloration, associated with a higher concentration of melanin, could reduce the damage caused by radiation in living organisms, by dissipating part of that radiation or reducing the action of free radicals.

The work, led by the researcher from the University of Oviedo German Orizaola Y published in the magazine Evolutionary Applications, constitutes one of the first suggestions of the existence of adaptive responses to radiation in vertebrates.

Chernobyl

The accident at reactor number 4 of the Chernobyl nuclear power plant (Ukraine) on April 26, 1986 generated the largest release of radioactive substances into the environment in history. “The initial impact of the accident on the nature of the area and on the human population was severe”Orizaola recalls.

However, more than three decades have passed since the accident and the area has become one of the largest nature reserves in Europe, refuge for species such as the wolf, the lynx or the brown bear. “Determining the long-term impact of an accident like Chernobyl on natural ecosystems has become a scientific and management priority”Add.

One of the aspects that currently arouses the most interest among the scientific community is the possibility that Chernobyl is generating radiation adaptation processes. The present study examined between 2017-2019 the coloration of 189 breeding males of the eastern san antonio frog (Hyla orientalis), both inside and outside the Chernobyl Exclusion Zone (Ukraine). This species, distributed in Eastern Europe and around the Black Sea, has a typical bright green coloration.

The work was carried out in 12 locations distributed along a wide gradient of radioactive contamination, from localities with levels more than one hundred times higher than usual, to four localities outside the Exclusion Zone and with basal levels of radiation. In addition to the coloration of the back, the dose of radiation absorbed by each frog was measured, as well as its levels of oxidative stress, which can be associated with both radiation exposure and melanin production.

darker frogs

The results showed that the coloration of the examined individuals is significantly darker within the Chernobyl Exclusion Zone than in the locations outside, until reaching completely black individuals in Chernobyl. Specifically, a direct relationship was detected between the color of the back and the distance of the sampling locations from areas of high radiation at the time of the accident.

The darkest individuals were found in or near the areas that experienced the highest levels of radiation in 1986. Practically all the frogs captured outside the Exclusion Zone showed the bright green color characteristic of the species. In contrast, no relationship was found between the frogs’ coloration and the radiation dose currently absorbed by those individuals. No increased levels of oxidative stress were detected either in the darker frogs, or in those with higher levels of absorbed radiation.

Differences in coloration

These results suggest that differences in coloration are not due to actual radiation exposure, and point to the effect of the historical exposure of these populations. This study suggests that the dark coloration of the Chernobyl frogs could be the consequence of a natural selection process generated by the initial exposure to very high levels of radiation at the time of the accident.

Individuals with a darker coloration, that is, with higher levels of melanin, would have suffered less impact from the radiation released by the accident. This greater protection would have increased its frequency within the population, up to the levels currently detected.

“The present study constitutes a very significant step forward in research work on the ecology of the Chernobyl Exclusion Zone”Orizaola concludes. «In addition, it opens new lines of research to examine the role that melanin can play in protection against radiation, with potential applications ranging from nuclear waste management to space exploration.”.

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