Chernobyl’s frogs are turning 'darker' to survive radiation—an eerie sign of nature’s desperate fight to adapt.

Almost four decades since the Chernobyl nuclear disaster, wildlife in the forests nearby is still giving researchers information about the behavior of animals towards the environment. An especially interesting observation is that in the Eastern tree frogs have darker skin in places with the highest exposure to radiation due to the 1986 disaster in Ukraine. This can be related to the benefits of melanin, the substance that gives darker color to living organisms.

According to a 2022 study published in Evolutionary Applications, exposure to radiation may have influenced the frogs' appearance over successive generations. Scientists believe that melanin, the pigment responsible for darker coloration, could have played a role in protecting some frogs against radiation-related damage. The research provides an example of how environmental pressures may influence the characteristics of wildlife, although the research has not yet established that radiation exposure alone caused the differences in skin color.

On April 26, 1986, a reactor at the Chernobyl nuclear power plant exploded during a safety test, releasing radioactive material into the surrounding environment. This resulted in contamination in Ukraine and neighboring countries as well, and evacuation, along with the creation of the exclusion zone, became necessary in the area of the nuclear power plant. As a result, over the following decades, the region's forests, swamps and abandoned settlements became habitats for various animal species, including the Eastern tree frog (Hyla orientalis).

Scientists' curiosity about these types of frogs was caused by the fact that their colonies were located in territories that were affected by radioactive radiation. Due to this, it became possible to study whether the presence of radioactive pollution in the environment over a long period is related to different features in frogs. Scientists examined the dorsal skin color of Eastern male tree frogs from northern Ukraine. Both frogs from the exclusion zone and from other territories were studied, which showed that frogs from the contaminated area had 43.6% darker skin compared to the frogs from areas away from the zone.

Research examined the potential function of melanin, a natural pigment that occurs on the skin and hair of both animals and humans. It provides dark pigmentation that is observed in amphibians as well. Therefore, the studies have shown that melanin might shield cells from some types of radiation through neutralization of harmful effects of the free radicals generated during the process. Ionizing radiation damages cells by targeting the genetic material and creating reactive compounds associated with oxidative stress. Melanin could prevent some of this damage due to its ability to absorb radiation and its antioxidant characteristics.

In the 2022 research, it was established that the frogs sampled closer to the site of the highest past exposure showed darker color. Nevertheless, there is no association between the skin color of the frog and individual exposure to the radiation in their environment. It is crucial to note the difference between these two findings, since the first one states that this phenomenon has happened under exposure conditions following the 1986 Chernobyl disaster. Moreover, no associations were observed between darkening of frog skin and their health status, such as body condition index and oxidative stress. Also, it was found that the skin color of the sampled individuals did not change within a short laboratory experiment. These data suggest that the darkening could be an evolutionary adaptation.

A 2023 study published in Chemosphere examined the liver of frogs living across the different levels of radioactive contamination. No significant liver damage was observed based on the radiation exposure of the animal. Also, no direct relationship was observed between the dark skin on the dorsal side and immune-related cells were present in the liver.

Another study published in Biology Letters in November 2024 examined whether current radiation exposure was associated with changes in the frogs' age, telomere length or corticosterone levels, a hormone linked to the stress response. The researchers studied 197 Eastern tree frogs over three consecutive years and found no relationship between individual absorbed radiation doses and any of these three biological measures. The findings suggest that current radiation levels may not be high enough to cause severe chronic damage to the species. However, they do not establish that radiation has had no other biological effects. .

The findings suggest that the 1986 Chernobyl disaster may have influenced the physical characteristics of wildlife living in the exclusion zone. The darker skin pigmentation observed in Eastern tree frogs is one example, with researchers suggesting that natural selection may have favored frogs with more melanin because it can help protect cells from radiation damage. However, this does not explain all the biological changes seen in the region. Further research is needed to understand how long-term radiation exposure has affected the genetics, health and survival of different species.