Scientific research has recently been published on the relationship between ionizing radiation and melanism in tree frogs in areas near the Chernobyl nuclear power plant in Ukraine. The study is carried out by Pablo Burraco and Germán Orizaola. The study shows that there is a relationship between the amount of melanin in the skin of frogs with respect to the amount of ionizing radiation they suffer in that region contaminated with radioactivity.
Human actions are altering ecosystems across the planet. It is one of the consequences of climate change that scientists no longer discuss. Among the pollutants released into the atmosphere by man, ionizing radiation is a potentially devastating threat to natural systems. The accident at the Chernobyl nuclear power plant (1986) represents the largest release of radioactive material into the environment.
The aim of the study was to examine how radiation exposure from the Chernobyl accident influences the dorsal skin colour of males of the Eastern Tree Frog (Hyla orientalis) sampled in a wide gradient of radioactive contamination in northern Ukraine. The relationship between frog skin coloration (which can act as a protective mechanism against ionizing radiation), radiation conditions, and oxidative stress levels was evaluated.
Skin coloration was darker in localities closer to areas with high levels of radiation at the time of the accident, while current radiation levels appeared to have no influence on skin coloration in Chernobyl tree frogs. Tree frogs living within the Chernobyl Exclusion Zone had a noticeably darker dorsal skin coloration than frogs living outside the Zone.
Melanism as an adaptive evolutionary resource
The results of this study suggest that the protective role of melanin previously detected at Chernobyl in smaller living organisms, such as fungi, may extend to wild vertebrates exposed to ionizing radiation. The tree frog being an amphibian can be used to know how a living being that lives on hybrid, aquatic and terrestrial life adapts, and that is also relatively fast generations (each generation is approximately 3 years).
Melanism in the Moth Industrial Revolution
Similar examples have existed in the history of biology. One is that of Britain’s moths and how population density changed due to the industrial revolution. Many moths in Britain possess two different shades of colour, a lighter “natural” shape and a darker melanic form (more melanin, skin pigment). This is an example of a visible evolutionary response and an industrial melanism in the speckled moth (Biston betularia).
There was a replacement, during the Industrial Revolution, of the typical pale common form by a previously unknown black form (carbonaria), driven by interaction between birds that prey on these moths and coal pollution. Predators ate the most common moth, the lightest, because it stood out in the bark of trees and that caused the population of the other dark moth to increase.
The darkest moth, with less survival success up to that point, during the industrial revolution became almost invisible by blending perfectly with the bark of trees that were full of polluting debris due to the industrial revolution that had just emerged. Several experiments showed that the melanic form enjoyed a survival advantage in polluted forests, while the opposite was true in uncontaminated areas. It seems that this effect of melanism can be related to pollution and protection against it.