Evolution in action as frogs in the Chernobyl exclusion zone turn black

Evolution is the result of environmental pressures that force species to adapt, and few environments exert pressures like the Chernobyl exclusion zone. A new study has revealed evolution in action, as frogs inside the radioactive zone appear to turn blacker than those outside the zone.

The explosion at the Chernobyl nuclear power plant in 1986 released a huge amount of radioactive material into the environment, and it is now at the center of an exclusion zone covering 1,000 square miles (2,600 square kilometers). If there is one of the worst disasters that humans have ever unleashed on the world, it is that the area has become a nature reserve that is home to a number of species.

This unique environment offers scientists an unprecedented glimpse into a microcosm of nature – in this case, evolution. How can animals within the exclusion zone adapt to the higher radiation levels in their environment?

In 2016, the new study team found some eastern tree frogs in the Chernobyl exclusion zone that were black rather than their usual bright green color. The researchers wondered if this was the result of natural selection from the higher radiation in the area.

To investigate, the team returned for follow-up studies over the next few years, collecting more than 200 eastern tree frogs from 12 lakes with varying levels of radioactive contamination, including four sites outside the zone for comparison.

And sure enough, they found that the closer the frogs lived to areas with high levels of radiation, the darker they were. Those people living inside the exclusion zone were an average of 43.6% darker than those outside, with some of them almost pitch black.

A gradient of samples of eastern tree frogs, from different locations with different levels of radioactive contamination

Why would this environment make the frogs black? The team says that melanin, the pigment that darkens the skin of animals, works to reduce cell damage caused by radiation. Normally this is UV radiation from the Sun, but it has also been shown to protect against ionizing radiation such as that present in Chernobyl. This means that people with darker skin will be less likely to experience cell damage after exposure to radiation.

The team hypothesizes that at the time of the accident, the frogs in the area that happened to be darker suddenly had an advantage at the new edges of that environment, meaning they were more likely to survive and reproduce. After three and a half decades and more than 10 generations of frogs, dark skin is now the norm in the exclusion zone.

It’s a fascinating little case study in evolution, and further work could help scientists better understand the effects of nuclear disasters and how ecosystems can recover.

The research was published in the journal Evolutionary Applications.

Source: The Conversation

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