Dogs in the Chernobyl exclusion zone
On April 25, 1986, a safety test was conducted on Chernobyl's Unit 4 reactor during a planned maintenance shutdown. Operators attempted to determine whether slowing the turbine could provide enough power to cool the reactor in the event of an outage. Miscommunication between the test engineers and plant safety staff led to the reactor operating under unstable conditions. The resulting power surge caused fuel damage, steam buildup, and two explosions early on April 26 — one from steam pressure and another likely from the buildup of hydrogen. The blasts ignited fires and released radioactive material into the atmosphere, prompting the evacuation of nearby residents within a 30-kilometer zone that later became known as the Chernobyl Exclusion Zone.
After the 1986 nuclear disaster in Chernobyl, the regional domestic dog population suffered from environmental pollution originating from the radiation. This disaster made the environment highly mutagenic, leading to various evolutionary processes including, but not limited to, bottlenecks, directional selection, and higher rates of mutation resulting in evolutionary trajectories that differ from unexposed animals.
History
Origin of populations
The exact origin of the populations of dogs living in the Chernobyl Nuclear Power Plant and the surrounding areas of the Chernobyl Exclusion Zone is unknown. However, it is hypothesized that these animals are the descendants of pets left behind during the original evacuation of Pripyat. Following the 1986 Chernobyl disaster, residents were ordered to evacuate with less than an hour's notice, leaving most of their animals behind. While many of these original pets population were killed by the Ukrainian Ministry of Internal Affairs to prevent the further spread of radiation, some dogs are believed to have survived by avoiding culling efforts and were soon after cared for by cleanup workers in the Exclusion Zone. Those that survived reproduced. There are currently two geographically and genetically distinct populations of dogs in the area, one in the CNPP and one in Chernobyl City. Scientists discovered this by implementing tracking and survey programs and conducting genetic analyses of the two dog populations. These studies showed limited gene flow and strong genetic differentiation despite the groups being only about 16 kilometers apart.Population and Genomic characteristics
In 2017, researchers launched the Chernobyl Dog Research Initiative after noticing that the number of stray dogs in the Exclusion Zone had grown dramatically, with estimates suggesting a population of more than 800 animals. In response, three temporary veterinary centers were tasked with examining and testing geographic diversity within the populations living within and outside of the Chernobyl Nuclear Power Plant. In total, blood was drawn from 302 dogs, 132 living inside of the CNPP which included the nuclear power plant itself, Pripyat 3km from the CNPP, Semikhody train station and the interim used fuel storage facilities ; 154 dogs in Chernobyl City 15km away from the CNPP, and 16 dogs in Slavutych, 30km of the CNPP. 129,497 single-nucleotide polymorphisms were tested and used to create a chloropleth map to measure the genetic similarities between these populations. The study found three genetically distinct populations that tend to gather in the chloropleth map based on location. These clusters showed that dogs from the same region were most closely related to each other. However, there was overlap with a small portion of the population from Chernobyl City clustering with each region. When dogs within the CNPP were analyzed against each other, Semikhody did not cluster, showing free-roaming tendencies and interactions with all regions; while ISF2 clustered with their own and NPP and Pripyat clustered with each other. This data suggests gene flow is restricted between groups in the CNPP and those outside of it.Using the same data collection, researchers measured individual dogs genomic heterozygosity within populations and discovered heterozygosity was highest in populations in Chernobyl City with average levels in Slavutych populations. This suggests that individuals in these populations have outbred while those within the CNPP have not. The low levels in CNPP populations suggest inbreeding.
Next, researchers measured kinship to purebred and free-breeding dogs in Europe, Asia, the Middle-East, neighboring countries and other Ukrainian cities by running principal components analysis - split into PC1 and PC2. The analysis of PC1 showed that dogs from Chernobyl were genetically different from dogs in Asia, the Middle-East and most purebred dogs but overlapped genetically with Shepherd breeds and free-roaming dogs and some eastern European populations. PC2 showed that dogs sampled within the NPP were genetically distinct from the dogs in Chernobyl City and beyond. Dogs from Slavutych did not form clusters, showing genetic links to purebred dogs, suggesting foreign ancestry. When researchers took a closer look they discovered that the dogs in the NPP specifically, were most closely related to Shepherd and eastern European breeds while dogs in Chernobyl City were most closely related to Roman-Mastiff breeds.
The data was later used to determine familial relationships within clustered populations. It was easy for the researchers to differentiate between ancestor and progeny but difficult to differentiate whether siblings were full-blood or half. Due to this, the researchers prioritized the former, discovering the presence of 15 distinct families. The first family was comprised of 162 individuals from various regions within Chernobyl, suggesting the presence of gene flow amongst existing populations. 7 of the 15 families were comprised only of one parent and one child while another family was related by a single individual from Pripyat, comprised of 10/14 individuals from the Semikhody train station. It was observed that males are habitual maters while females only mate when in heat. These results suggest there is a complex social structure of mating and that it happens across regions in Chernobyl.
Lastly, when researchers compared DNA from their data set to purebreds they discovered that dogs in the NPP had a higher frequency of similar alleles to their purebred counterpart than those outside of this zone. Due to these free-roaming dogs being isolated to a highly radioactive area, they partake in increased levels of inbreeding. Their related ancestry is displayed in the similarity to their ancestors while dog populations in Chernobyl City, where humans have returned, are outbreeding with other dog populations.
Life in the Exclusion Zone
At present there is estimated to be over 700 dogs living in the Exclusion Zone with little growth in the population's numbers. While litters are born each year, the dogs are at risk of facing aggression from local wildlife, namely packs of wolves. This drives them out of the surrounding forests, bringing them closer to power plants and human activity. These aggressive interactions with wild animals are the main source of rabies in the population. Their lack of innate survival skills makes them reliant on humans and unable to live independently. In addition to rabies, the dogs face harsh environmental conditions and may die due to hypothermia, radiation exposure, malnutrition or car collisions, all contributing to an average lifespan of just 3-6 years old.The dogs are not fully isolated from humanity, as there are 3,500 people each day who work in close proximity, providing care where they can. This has become increasingly difficult due to worries of rabies infection alongside the COVID epidemic. Despite this, in 2017, the Clean Futures Fund created a program 'Dogs of Chernobyl' where three veterinary clinics opened to provide treatment for dogs with parvovirus, rabies, hepatitis and distemper. The non-profit is also in charge of neutering the strays in an effort to control the population and provide them with sustainable care, resulting in reduced birth rates and healthier individuals.
Researcher Jonathan Turnbull, cultural and environmental geographer of Cambridge University's geography department, documented how guards and workers within the exclusion zone frequently developed relationships with these dogs. Guards stationed at checkpoints may build them shelters, provide them with scraps and other leftovers as well as administering basic care like tick removal. In return for the guards' care, the dogs ward off encroaching wolves and provide entertainment along with needed companionship. In 2016, an initiative called the New Safe Confinement began, which would place a structure over the destroyed Reactor 4. However, when it was completed in 2019, most of the guards and employees had no plans to return to the CEZ depleting the dogs food supply. The CFF stepped in shortly after, setting up food and water stations to ensure the populations could sustain themselves. After the Russian invasion of Ukraine in 2022, which led to the Capture of Chernobyl resulted in over 300 staff on duty at the time being held hostage and the dogs being briefly left without supervision and care.
The 2019 documentary film "Fallout Dogs" directed by Julia Oldham follows the activities of stray dogs around the Chernobyl Exclusion Zone. Oldham, a multimedia artist known for exploring relationship between nature and technology, features a local translator and tour guide of the Exclusion Zone in said film and highlighted the local's personal efforts to care for the dogs by way of feeding and interacting with them frequently.