Reflections on the Black Tree Frogs of Chernobyl

A tree frog shown before and after the 

Chernobyl nuclear accident in 1986

 

 

I. 

 

I have always liked D. H. Lawrence's description of little green frogs as gem-like [1].

 

But it seems that the frogs living in the Chernobyl Exclusion Zone (CEZ) are no longer emerald green in colour. For in order to increase their survival rates in an irradiated environment, the frogs have undergone rapid evolution and now model jet black skins rich in protective melanin [2].

 

In 2016, whilst researching the effects over the previous three decades of Chernobyl's uniquely polluted environment on the flora and fauna, two Spanish scientists [3] made a strange discovery ... 

 

They expected to find that plant and animal species subjected to daily doses of radiation way above normal levels would have experienced negative consequences, but what they did not anticipate was that nature would respond in such an amazing way and recover so quickly - and they certainly weren't on the lookout for black frogs!

 

 

II.

 

So, what on earth is going on here? 

 

Well, cancer resistant wolves [4] and ebony-skinned tree frogs would seem to suggest that the Chernobyl disaster, which generated the largest release of radioactive material into the environment in human history, has accelerated natural evolution in a manner that Darwin - who always liked to stress the slow and gradual nature of evolutionary change by natural selection [5] - would have found hard to believe.   

 

And this - along with the absence of human beings - helps to explain why Chernobyl has become one of the largest nature reserves in Europe, where a diverse range of endangered species find refuge and live happily (or at least successfully) side-by-side. 

For whilst acute exposure to high doses of radiation can cerainly be damaging, both to the natural environment and the genetic material of living organisms, it can also kick-start and accelerate evolution in a surprisingly positive way, as species adapt to the new conditions. 

 

 

Notes

 

[1] See D. H. Lawrence, 'The State of Funk', in Late Essays and Articles, ed. James T. Boulton, (Cambridge University Press, 2004), p. 221. 

 

[2] The pigment melanin which, as many people know, reduces the effects of ultraviolet radiation, can also, so it seems, afford protection against ionising radiation. And that's why it's better to be a black frog than a green frog if you're going to spend your life hopping about in the CEZ.   

 

[3] Germán Orizaola and Pablo Burraco; they discuss their study of over 200 male tree frogs taken from twelve different breeding ponds from various sites in northern Ukraine - including four outside the CEZ - in an article originally published on theconversation.com (28 Sept 2022): click here.  

      As Orizaola y Burraco make clear, the dark skin colouration is typical of frogs from within or near the most contaminated areas at the time of the Chernobyl disaster and it suggests that they have undergone a process of rapid evolution in response to the radiation. The black frogs, having better survival rates, are now the dominant type within the CEZ, which, in my view, is a bit of a shame, as I prefer the little frogs with bright green skins. 

 

[4] See the recent post entitled 'Cara Love and the Mutant Wolves of Chernobyl' (14 Feb 2024): click here.

 

[5] In what is considered to be the founding text of evolutionary biology - On the Origin of Species (1859) - Darwin emphasises how natural selection progresses at a glacial pace and we usually observe nothing of the changes being made until long periods of time have passed. 

      Although this is true, adaptation to new conditions can occur within a relatively short period of time and examination of the fossil record shows that many species undergo rapid bursts of evolution, even if true speciation takes time. Recent work in developmental biology has identified certain mechanisms of tissue morphogenesis that may help explain any swift structural transitions. 

      I am grateful to Dr Andy Greenfield - my go to science guy and longtime friend - for his guidance on this point.

 

 

For a frog-related follow-up post to this one, click here.

 

 

Last Rat Standing (Darwin and Bond in the Age of Coronavirus)

New York City rat (photo by Christopher Sadowski) 
and Javier Badem as Raoul Silva in Skyfall (2012)

There's a lovely scene in the Bond film Skyfall in which the villain, Raoul Silva, played by brilliant Spanish actor Javier Badem, tells the story of his grandmother's solution to the problem of rats when they infest the tiny island on which she lives:

"They'd come on a fishing boat and gorged themselves on coconut. So how do you get rats off an island, hmm? My grandmother showed me. We buried an oil drum and hinged the lid. Then we wired coconut to the lid as bait. The rats would come for the coconut and they would fall into the drum. And after a month, you've trapped all the rats. But what did you do then? Throw the drum into the ocean? Burn it? No. You just leave it. And they begin to get hungry. Then one by one, they start eating each other, until there are only two left. The two survivors. And then what - do you kill them? No. You take them and release them into the trees. Only now, they don't eat coconut anymore. Now they only eat rat. You have changed their nature."

I thought of this when I read about the plight of rats in NYC (and elsewhere) during the coronavirus pandemic. Thanks to the so-called lockdown, many of their favourite feeding places - such as the bins at the back of restaurants - are no longer viable options, forcing these resilient rodents to resort to desperate measures. Not only are they fighting one another for food, but some have turned cannibalistic and are devouring their own kind.

The fact is, the threat of starvation makes rats - like people - behave in extremely different ways; they effectively change their nature, as Sr. Silva would say.

I suppose, in the end, this will give them an evolutionary kick up the arse and result in a future breed of stronger, more aggressive, more resourceful rats (survival of the fittest being the popular name for the mechanism of natural selection we can witness at work here).    

Notes

Skyfall (2012), dir. Sam Mendes, starring Daniel Craig (as James Bond) and Javier Bardem (as Raoul Silva): click here to watch the scene I mention above.