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Chernobyl's Dogs Have Become Genetically Distinct. Is Radiation To Blame?

A group of dogs of different colors standing on asphalt.
A pack of free-roaming dogs that lives within the industrial areas of the Chernobyl Nuclear Power Plant. Credit: Tim Mousseau
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A new study examining the growing population of dogs living in and around the Chernobyl exclusion zone has revealed how isolation and complex family structures have affected their genetics.

The upcoming edition of Crufts dog show is a yearly reminder that genetic pressures are a huge burden on purebred dogs. A campaign to remove flat-faced dogs like pugs and French bulldogs, which suffer from a litany of conditions due to the exaggeration of certain traits through selective breeding, has gained momentum. Larger breeds face other genetic issues – from Labradors’ hip dysplasia to German Shepherds’ degenerative myelopathy.

But the majority of dogs on Earth aren’t purebred.

Our planet is home to roughly 1 billion dogs, of which 75% are thought to be freebreeding. For many of these animals, environmental rather than genetic threats are their main concern.

But the feral dogs studied by Gabby Spatola, a PhD student at the University of South Carolina, face a unique cocktail of hazards. That’s because the abandoned buildings and overgrown streets they call home sit in the shadow of the Chernobyl Nuclear Power Plant.

The left-behind dogs of Chernobyl

After a catastrophic meltdown led to a vast leak of radioactive material from the stricken structure in 1986, Soviet authorities instituted a 30-kilometer “exclusion zone” around the plant. The nearby town of Pripyat (population ~50,000) was infamously abandoned.

In the absence of humans, the local flora and fauna has reckoned with high background radiation levels. While population censuses of large mammals show that red deer and wild boar populations within the zone are comparable to those outside it, bird and butterfly populations remain significantly lower in highly contaminated areas.

This unusual ecosystem was never meant to contain dogs. After the establishment of the exclusion zone, local authorities ordered the mass cull of left-behind pets, fearing that they would spread radioactive contamination. But some hounds escaped their hunters and, living in Pripyat and even in the ruins of the Power Plant itself, started building a new population.

By 2017, things had gotten out of hand.

“The population started to get really, really large,” explains Spatola in an interview with Technology Networks. “The higher-ups at the power plant were starting to get worried about the number of dogs.”

A brown and black dog in undergrowth near a pipe.

Credit: Jordan Lapier

To lend a hand, University of South Carolina’s Professor Timothy Mousseau established a series of clinics around the exclusion zone as part of the Clean Futures Fund, a non-profit set up to improve animal and human health in the area.

The clinics captured dogs, provided them with veterinary care, spayed or neutered them to try and reduce the expanding population and took blood samples. In 2018, Spatola joined the project, visiting the clinics with the long-term aim of characterizing how these dogs’ unique environmental context affected their behavior, population structure and genome.

A new paper, which features Spatola as first author and Mousseau as senior author alongside the National Human Genome Research Institute’s Elaine Ostrander, has now analyzed these Chernobyl dogs’ unique genetics.

A genetically distinct population

The team set up three clinics in total. One clinic, which sampled 154 dogs, was in Chernobyl City, located 15 km from a second camp within the Power Plant itself that was able to survey 132 dogs. A smaller clinic was positioned 45 km away in the city of Slavutych, where many of the Plant’s workers and their families were moved in the wake of the disaster and where 16 dogs were captured and sampled.

One of the study’s key strengths, says Spatola, was including data from 281 village dogs and 1,324 purebred dogs from outside these areas for comparison. “The fact that we had such a large data set of purebred dogs as well as other village dogs from all different parts of the world, this really allowed us to get a sense of what is normal for a village dog population.”

The analysis showed that Chernobyl dogs are genetically distinct from other village dog populations. The team showed that while dogs in Slavutych, and to a lesser extent Chernobyl City, had ancestry from non-native dog breeds, the dogs in the Power Plant had significant genetic influence from breeds that were likely to have been those common in the area around the time of the disaster, like German shepherds and Russian hounds. “It's very likely that these dogs have been around probably since the time of the disaster, maybe even before,” says Spatola.

Spatola explains that the Power Plant, perhaps surprisingly, is an ideal spot to build a community of feral dogs. The large number of abandoned buildings in the area provide the animals with shelter, while a steady stream of maintenance workers who still visit the plant, alongside regular influxes of tourists, give the dogs a food supply.

While the area is still highly radioactive, the dog community seems unfussed. A pack even lives in the storage facilities that house spent nuclear fuel. “These dogs, like typical village dog populations, only live to be about three or four years old,” says Spatola. While the animals are likely to be at a higher risk of cancer, in the face of exposure, predation and conflict with other dog groups, not many are likely to survive long enough to become ill.

Inbreeding and genetic drift

But cancer is just one consequence of exposure to a mutagenic environment. What other impacts could living in perhaps the most radioactive habitat on earth have on these dogs’ genomes? Spatola says this will be her project’s next focus. The current study represents a necessary foundation for future research. In particular, the research team identified that their analysis would be complicated by the Power Plant’s homebody dog population. With limited movement in and out of the plant, the family dynamics among dogs in the area have become inbred and highly complex. One loose family was identified that comprised 162 individuals spread across different capture locations.

This level of inbreeding and isolation is a roadblock for geneticists, making it harder to tease out the impacts of environmental exposure against a background of genetic drift, where unusual mutations are likely to have seeped into the gene pool.

Instead, the team will need to use purebred dog genomes as references. “The dogs’ ancestry with German Shepherds gave us the idea of looking at the German Shepherd background. If it's probable that they've been in the area since the time of the disaster, they likely came from pets. We can use the German Shepherd background to determine the accumulation of mutations,” Spatola explains.

The researchers hope that this information will prove integral to our understanding of how long-term radiation exposure might affect large mammal populations. As for the dogs, the population remains healthy, with Mousseau making his most recent visit just prior to the invasion of Ukraine by Russian forces in 2022. Through the clinics, Spatola explains, “We plan to do as much as we can for them, keeping them fed and healthy.”

For these dogs, which have reckoned for over thirty years with the consequences of human activity, the threat of war represents just another challenge for them to face.

Reference: Spatola GJ, Buckley RM, Dillon M et al. The dogs of Chernobyl: Demographic insights into populations inhabiting the nuclear exclusion zone. Sci. Adv. 2023;9: eade2537. doi: 10.1126/sciadv.ade2537