More than three decades ago – on April 26, 1986 – reactor number 4 at the Chernobyl Nuclear Power Plant exploded and, as a result, large amounts of radioactive substances were released into the atmosphere, such as cesium-137 or iodine-131, among others. . The authorities established the Chernobyl exclusion zone (ZEC) in a radius of 2,600 km2 and evacuated the population, telling them not to take their pets with them because they could be contaminated with radiation. Many animals were euthanized by Soviet soldiers to prevent the spread of radioactive contamination, but some hid in nearby camps and empty buildings and managed to survive…and reproduce.
A study has now analyzed the genetics of 302 feral dogs that live next to this nuclear power plant or in Pripyat (the closest town), or in areas located between 15 and 45 kilometers from the place where the catastrophe occurred. Its authors affirm that they present genetic differences depending on the distance they are from the plant and that they differentiate them from other populations of dogs, making them genetically unique.
The findings, which have been published in Science Advances, could reveal both the long-lasting effects of radiation in animals and genetic traits that could have helped certain dogs avoid the worst effects of the disaster on their health. Although the authors acknowledge that it is early to say whether the radioactive environment has contributed to these unique genetic profiles of the Chernobyl dogs, they state that their study “presents the first characterization of a domestic species at Chernobyl, establishing its importance for genetic studies on the effects of long-term exposure to low-dose ionizing radiation”.
“This is an important and rigorous study that lays the foundation for studying whether continued radiation exposure could scar the genome, a pressing issue for animals and humans.”
The researchers took blood samples from these dogs and compared them with those of dogs from different countries and with that of stray dogs living in Vinnitsa, a Ukrainian city located 350 kilometers southwest of Chernobyl. The results of the analysis, according to these scientists, allow the animals to be classified into three different populations from the genetic point of view depending on the distance they live from the plant, which suggests that radiation exposure could have affected more the genes of some individuals than those of others.
In the effects of ionizing radiation, oxidative stress and cell and DNA damage stand out, which depends on the dose received and the exposure time, but the authors of the study have not published data on the alterations experienced by these dogs or if they have found changes in the mutation rate. These scientists have identified a total of 15 complex family structures unique to the Chernobyl population compared to other dogs around the world. They also found wide genomic variations within and between geographic locations in the ZEC, “suggesting that these dogs move between locations, live close to each other, and reproduce freely,” they state in a press release.
The dogs they have studied do not share any external differential characteristics. Gabriella Spatola, a biologist at the University of South Carolina (United States), has acknowledged in statements to elDiario.es that they have not carried out genetic expression studies, nor have they detected more prevalent diseases in these animals: “This is not something that we have investigated in the study”.
Although they have verified that their life expectancy is shorter –3-4 years compared to the 10-12 years that a domestic dog can live– they do not necessarily attribute this to radiation, but rather consider it likely due to being dogs Strays have to endure extreme weather conditions (cold winters) and do not receive the same care as pets at home, although many are fed by guards and receive veterinary care by the Chernobyl Dog Research project, an initiative launched March in 2017.
Researchers have warned that it is still unclear how far dog populations have expanded since their 1986 ancestors, how many different populations remain, how diverse these populations are, or whether they are limited by geographic restrictions. In his opinion, “the understanding of the biological foundations of animal and human survival in regions where environmental aggression is high and continuous” is the greatest potential of this research.
It does not test the possible effects of radiation on living things.
Several experts do not consider the results of the study relevant because they consider that it does not provide evidence on the possible effects of radiation exposure in these animals. Germán Orizaola, a researcher at the Mixed Institute for Biodiversity Research at the University of Oviedo, explained in statements to SMC Spain: “From my point of view there are many limitations to consider the study as relevant from the point of view of the effects of radioactive contamination on living organisms. The main one is that radiation exposure is not measured in any of the individuals studied, and therefore makes the study uninteresting, as such, from the radiological point of view”.
“This study in no way links differences in dog population structure to the current radiation at Chernobyl.”
“A worrying aspect is the fact that the authors do not seem to distinguish between the initial effects of the accident and the current situation, more than three decades later with a radical change in radiation levels and the identity of radioactive substances. The article insists that the accident generated “an ecological catastrophe of massive proportions” and “that many species have not recovered from the consequences of the catastrophe” (without providing data to support these claims), ignoring the work that indicates that Currently, the Chernobyl Exclusion Zone is one of the largest nature reserves in Europe, an example of passive renaturation processes, and with clear and abundant examples of species with notable population increases”.
James Smith, professor of environmental sciences at the University of Portsmouth (United Kingdom), also states in statements to SMC Spain: “This study analyzes the structure of the dog population in Chernobyl and concludes that they had different population structures from other two populations of dogs that lived in freedom. However, it is important to note that this study in no way links differences in dog population structure to the current radiation at Chernobyl. It just shows that there is a different mix of breeds and families in Chernobyl compared to the other locations, which is not a surprising finding given that the current population depends on the particular mix of breeds that survived the culling of domestic animals in 1986, as well as well as later introductions.
“I think the article could mislead the reader by stating that ‘although some species appear to have recovered – probably due to the absence of human disturbance – many have not’, quoting an article edited by me, when in fact our article does not in any way support the authors’ claim that many have not been recovered. I am surprised that the authors do not clearly state in the article that their results do not demonstrate that radiation is causally related to differences in the Chernobyl dog population structure. I am also surprised that the title of the press release states that ‘Chernobyl dogs may be genetically distinct due to different levels of radiation exposure’, when the article presents no evidence to support a causal relationship between population structure and the radiation dose.
“That is not to say that the extremely high radiation doses in some areas during the first weeks after the accident could not have had a significant impact on the populations of domestic and wild animals. The lack of evidence in this work also does not show that there were no effects of radiation on the animals in Chernobyl.”
For his part, Stephen Chanock, director of the Cancer Epidemiology and Genetics area of the National Cancer Institute of the United States, seems to have found the most interesting work and affirms to SMC Spain that “It is a magnificent study of changes in the Genetics of dog populations at and around the Chernobyl site. The authors have carefully assessed how changes in kinship have changed under the pressure of a restricted environment, here driven by zones established to contain animals roaming regions contaminated by radiation that persists after deposition after the 1986 accident. ”.
“This study is a first step to assess how and in what way exposure to environmental ionizing radiation (in this case Cesium-137) might affect subsequent generations, something that was not reported – or evaluated – in this study of common variants shared among dogs. This is an important and rigorous study that lays the foundation for studying whether continued radiation exposure could scar the genome, a pressing issue for animals and humans.”
“The work is well done and provides fascinating details about dog populations under severe pressure. [Sin embargo] the study design does not allow one to explore the actual changes in the genome due to extensive radiation exposure. Hopefully the next study will address this question, and it is important to do so in the same population studied here to better understand how constant exposure to ambient ionizing radiation affects the genome.”
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