Chernobyl stray dogs are genetically different

Genetic analysis of the dogs near the Chernobyl nuclear power plant in Ukraine shows that they are different.

But there is no proof that it is due to radiation.

A study carried out on more than 300 feral dogs indicates that genetic affinity changes with increasing distance from reactor number 4, which exploded in 1986. However, these differences could be due to causes that have nothing to do with the release of material radioactive or its levels are harmful in the long term.

In fact, the area is witnessing a brutal explosion of wildlife.

On April 26, 1986, reactor number 4 of the Vladimir Ilich Lenin power plant, 17 kilometers from Chernobyl (in the north of the country), suffered the biggest nuclear accident in history.

For days, large amounts of radioactive material, including cesium-137, iodine-131, and other radionuclides emitting ionizing radiation, were burned and released into the atmosphere.

Weeks later, the Chernobyl exclusion zone (ZEC) was created in a radius of 2,600 km², evacuating all the inhabitants.

Within the containment program, the Ukrainian Ministry of Interior, then within the Soviet Union, ordered the euthanization of all pets.

But some dogs escaped the purge.

How have the dogs fared in an environment that was initially so adverse?

As for the number, it seems that good.

Currently, according to the Chernobyl Dog Research Initiative census, there are more than 800 feral dogs in the area.

For Tim Mousseau, a biologist at the University of South Carolina (United States) and senior author of this new study, "anything we learn about how they survive in this environment will be of direct relevance to humans in Chernobyl and other radioactive environments." .

To do this, they took blood samples from 302 specimens.

Almost half live around the power station and Prípiat, the closest town, which today has become a ghost town.

Another 150 are from Chernobyl itself, 17 kilometers from ground zero.

And the remaining 16 wander through Slavutich, also a Ukrainian population,

The blood from the samples allowed them to map genetic similarity.

The results of this work, published in the scientific journal

, indicate that these dogs are genetically different from other dogs from various countries that they analyzed for comparison.

They are also from stray dogs captured in Vinnitsa, a Ukrainian city located 350 kilometers southwest of Chernobyl.

The study goes even further: the animals in the study are grouped into three large populations from the genetic point of view and belonging to one group or another depends on the distance from the plant.

This suggests that radiation exposure might have affected the genes of some more than others.

But there is no data, for now, of this having happened.

In principle, and being highly dependent on the dose and exposure time, ionizing radiation causes oxidative stress, cell and DNA damage, among other effects.

However, the authors of the work have not published any data on alterations in dogs, especially if they have observed changes in the mutation rate.

Mousseau has been going to Chernobyl for twenty years (until the war broke out), almost as long as he has been warning of the damage that radiation would be doing.

"We have carried out preliminary studies of the external and internal doses to these dogs and we have an article under review that covers part of this question," recalls Mousseau in an email.

One of the problems with the thesis of this biologist, an expert in the impact that the environment has on genes, is that it runs into reality.

After the 1986 disaster, which must have cost the lives of countless living beings, the exclusion zone has become almost a paradise on earth.

After the evacuation of the Adams and Eves and the abandonment of the fields, both the flora and fauna have thrived in the entire area around the power station.

A work published in 2015 and that had a great impact showed that, indeed, the presence of large mammals was reduced in the first years after the accident, but they recovered immediately.

Aerial surveys conducted since the 1990s show that moose, deer, roe deer, and wild boar populations were similar to those in other regions.

And, in the absence of humans,

“Most research clearly shows that many organisms living in the most radioactive regions of the exclusion zone have severe injuries of many types”

Tim Mousseau, biologist at the University of South Carolina, United States

“Many studies now suggest that in the parts of the exclusion zone that are not particularly radioactive, many animals have done very well, especially those that are hunted in other areas outside the zone,” Mousseau acknowledges.

“However, most research clearly shows that many organisms living in the most radioactive regions of the exclusion zone have severe injuries of many types,” she adds.

So we will have to wait for the second part of her investigation, already with the radioactive exposure data, to find out how the dogs are doing.

Jim Smith is a biologist at the University of Portsmouth (UK) and, like Mousseau, has been going to Chernobyl for several years.

He is the main author of that work on wolves and other large mammals and has participated in several censuses of wildlife in the region.

“In our 2015 study we were unable to find evidence linking mammalian populations to radiation dose and found mammalian population densities similar to other nature reserves in Belarus,” whose border is less than 20 kilometers away.

"I haven't looked at their situation since then, but other scientists have found similar results," he adds.

“In the absence of human pressure, wildlife thrives despite the potential influence of chronic low-level radiation”

Jim Smith, biologist at the University of Portsmouth, UK

For Smith, the genetic part of Mousseau's research is impeccable, but he rejects that it can be connected to radiation exposure.

“All radiation (including natural radiation from rocks, X-ray scanners, cosmic rays…) can damage DNA, so the radiation at some Chernobyl hotspots is surely influencing the genetics of animals. .

But the question is to what extent is it happening and does it affect populations significantly,” he says.

The problem is that there are so many other environmental factors, so "it's hard to find clear effects of radiation on individuals, even in the most contaminated areas," he adds.

And he ends: However, what is clear to me is that, in the absence of human pressure,

Like Mousseau and Smith, many other scientists from various disciplines from around the world frequently visit Chernobyl. Unfortunately, it is the largest experiment to study the impact of radiation on life.

One of them is the biologist from the University of Oviedo Germán Orizaola, who has a laboratory in the city thanks to a collaboration with the Center for Nuclear Safety, Radioactive Waste and Radioecology of Chernobyl.

A few years ago he published a paper on Przewalski's horses.

About thirty of these wild equines were released into the exclusion zone in 1998, 12 years after the explosion without much ecological logic at first.

In the article, Orizaola wrote: “Initial predictions indicated that, due to radioactive contamination, the area would be uninhabitable for more than 20,000 years.

It was thought that Chernobyl would become a desert for life.

However, at present there are already about 200.

On the right, a San Antonio frog captured outside the exclusion zone.

On the left, a frog of the same species ('Hyla orientalis') from a pond near reactor number 4. Germán Orizaola

But the realm of Orizaola is actually amphibians, especially the San Antonio frog, a small frog with an intense bright green color.

However, as the scientist from the University of Oviedo studied and verified, the closer to the power station, the darker they are, to the point that those of the nearby ponds are completely black.

Like Mousseau in his study with dogs, Orizaola and his colleague Pablo Burraco measured ambient radiation.

But what Mousseau did not do (at least he has not published it), was to measure the existing radiation inside the animals, specifically the presence of cesium in the muscles and strontium in the bones.

What is striking is that they found no relationship between the coloration of the frogs and the dose of radiation absorbed at present.

In a note from the University of Oviedo, they explain the apparent mystery: "These results suggest that the differences in coloration are not due to current exposure to radiation, and point to the effect of historical exposure of these populations."

In other words, the dark coloration of the Chernobyl frogs would be due to an initial exposure to very high levels of radiation, not from current frogs, but from those that lived there in 1986. The greater or lesser melanin protects from radiation, thus that darker amphibians would have suffered less from the radiation released by the accident, having a greater chance of surviving.

"In dogs or in any other animal, the key is to determine the radiation exposure," recalls Orizaola and is one of the critics he makes of the study of the Chernobyl dogs.

But he has others.

“The initial number of dogs that survived the hunt initiated after the explosion is unknown, which introduces the bias of the founding dogs,” adds the biologist.

A very small initial population favors genetic differentiation.

“In addition, the radiation of 1986 has nothing to do with the current one.

It has been reduced by 90% and the most dangerous compounds have disappeared.

His final judgment on the study of dogs is summed up in one sentence: "They are as different as the dogs of Warsaw and those of Krakow," he says.

Both Polish cities are relatively far from the center.

The ecologist from the National Museum of Natural Sciences, Ismael Galván, worked with Mousseau in the study of the birds of Chernobyl.

From those resulted a study published in 2014 with such interesting conclusions that they raised a certain amount of dust then.

They studied the impact of radiation on 16 species of birds.

Their conclusion literally reads like this: "Birds improve their levels of antioxidants and their body condition and decrease their levels of oxidative stress and DNA damage with the increase in background radiation to which they are exposed in Chernobyl."

That is, the birds do not appear to be affected by radiation exposure.

As Orizaola also said, "Chernobyl is experiencing an explosion of life," says Galván now.

Regarding the dogs, Galván acknowledges that the data shows that they are genetically different, so the radiation hypothesis does not seem problematic to him.

"Genetic differentiation may be the basis for the adaptation that we saw in birds," he says.

"It is likely that the animals have adapted to low but chronic radiation levels over time, leading to a physiological adaptation," he adds.

The problem is that there is a lack of data on the physiology of dogs.

The key could be in a word that you have to look up in the dictionary: hormesis.

“When an organism is exposed to something harmful that the metabolism has to fight or face [a chemical agent, environmental damage, radiation...], the final state can be better than the initial one”, explains Galván.

It is the scientific version of what does not kill, makes you fat.

"It is obvious that radiation is not good, but animals, through generations, have the ability to adapt," says this researcher.

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