Biology

Evolution in action as frogs in Chernobyl exclusion zone turn black

Evolution in action as frogs in Chernobyl exclusion zone turn black
Two specimens of Eastern tree frog at the extremes of coloration. The left one was taken from within the Chernobyl exclusion zone, while the right one was found outside the zone
Two specimens of Eastern tree frog at the extremes of coloration. The left one was taken from within the Chernobyl exclusion zone, while the right one was found outside the zone
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Two specimens of Eastern tree frog at the extremes of coloration. The left one was taken from within the Chernobyl exclusion zone, while the right one was found outside the zone
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Two specimens of Eastern tree frog at the extremes of coloration. The left one was taken from within the Chernobyl exclusion zone, while the right one was found outside the zone
A gradient of Eastern tree frog specimens, from various locations with differing levels of radioactive contamination
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A gradient of Eastern tree frog specimens, from various locations with differing levels of radioactive contamination

Evolution is the result of environmental pressures forcing species to adapt, and few environments exert pressures like the Chernobyl exclusion zone. A new study has revealed evolution in action as frogs within the radioactive region seem to be turning 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 encompassing 1,000 sq miles (2,600 sq km). If there’s a silver lining to be found from one of the worst catastrophes humans have ever unleashed on the world, it’s that the area has become a nature reserve that houses a range of species.

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

In 2016, the team on the new study found a few 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 ponds with different levels of radioactive contamination, including four sites outside the zone for comparison’s sake.

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

A gradient of Eastern tree frog specimens, from various locations with differing levels of radioactive contamination
A gradient of Eastern tree frog specimens, from various locations with differing levels of radioactive contamination

Why would this environment turn frogs black? The team says that melanin, the pigment that darkens the skin of animals, works to reduce cell damage caused by radiation. Normally that’s ultraviolet radiation from the Sun, but it’s also been shown to protect against ionizing radiation like that present at Chernobyl. This means that individuals with darker skin will be less likely to experience cell damage after radiation exposure.

The team hypothesizes that at the time of the accident, frogs in the area that happened to be darker suddenly had an advantage in the new extremes of this 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 into evolution, and further work could help scientists better understand the impacts of nuclear disasters and how ecosystems can recover.

The research was published in the journal Evolutionary Applications.

Source: The Conversation

8 comments
8 comments
Pupp1
It may be premature to consider this to be evolution. Darwin's finches were thought to be a great example of evolution, because isolate populations had different sizes of beaks. Until very recently, evolutionists thought these changes evolved over a period of 2.3 million years. But years ago, a group of finches was introduced into an island without finches, to see if they could document how they change.

The researchers sort of forgot about them, until they checked 17 years later. Over that time, the birds developed very significant changes, that were consistent with the new environment. It looks like these birds are pre-programmed with the ability to change features in response to pressure from the environment, via. regulatory genes, that used to be called junk DNA.

These frogs may not have developed any new genetic ability, but like the finches, they had the pre-programmed ability to be darker when needed.
Marcom
That’s quite correct @Pupp1. There seems to be a misunderstanding that confuses everyone. The frogs changing colour is clearly a process of adaptation, this is not evolution. If by evolution biologists mean to say that a species changes to a different kind of species, e.g. a cat to a dog, then clearly this is not evolution, the frog is still a frog and it didn’t take millions of years for the adaptation to occur.
Douglas E Knapp
You are correct that gene expression is influenced by environment so clearly we need some froggy DNA to check out who is correct.

On the other hand evolution does not take millions of years. It could happen in one generation but normally goes slowly UNLESS there is a big environmental shift such as in this case.

Next point, evolution of one species to another is based on whether the two kinds can mate and have kids that can mate. If not then they are two species. It is STILL evolution even if the animals are not changing into a new species!
TechGazer
The changes in frogs and finches doesn't seem like pre-programming. Some species might have a larger collection of previously-useful genes that get expressed in some of their spawn. The environment determines which of those descendents survive to reproduce, and which genes are kept or 'at the front of the queue for expression' (there's probably a proper scientific term for that). 17 generations of finches seems long enough for significant evolutionary changes. 36 generations of frogs seems long enough too.

Evolution only requires a .3% improvement in reproduction to dominate. The rate of death or reproductive failure for frogs around Chernobyl was probably much higher than that, which increases the rate of evolution. I'm sure there have been experiments with 100% selection (killing off any spawn with or without a specific trait). How many generations does it take to change, for example, a Dalmation to be either pure white or pure black if you applied 100% selection?

Those frogs would also have a higher mutation rate due to the environment, which would increase the rate of evolution.
NMBill
When the frog turns into a new species of newt, let me know.
Pupp1
TechGazer, If the frogs did not have the genetics to produce melanin, and then in a generation or two genetic mutation created all the genes necessary to product melanin, that would be evolution. But the study (click the link in the article to the original article) seems to acknowledge that the frogs already had the ability to produce the melanin.
The interesting thing about epigenetics, is that it allows a parent to pass a trait they acquired in life, to their dependents. Though, another possible mechanism, is that the epigenetic part of the DNA are designed to vary a bit from generation to generation. So, the finches, or the frogs, each vary a bit from their parents. So if there is an environmental stress or change, each generation is able to shift a bit further away from the first generation. Natural selection being the driving force. But, the pre-programmed ability to shift colors or beak sizes, has to be there first.
150G
Some frogs were already being born black. It sounds like green frogs were just selected out. Cool info non the less.
fen
It would be interesting to take the black frogs and see how long it takes them to adapt back to green, if given a more favourable environment. I have always thought that turning darker was easier than lighter, shedding protection harder than gaining protection. But thats just from observing a german turning as dark as a spaniard after 2 weeks of sun, and taking a lot longer to lose the tan, when we get to this level of protection how long to shed.