Chernobyl Dogs Rapid Evolution: A New Generation of Resilient Canines

The Chernobyl dogs have undergone a remarkable transformation, adapting to their harsh environment in a way that's both fascinating and heartbreaking. They've developed a robust immune system, capable of fighting off radiation-induced illnesses.

Their coats have also changed, becoming thicker and more protective against the elements. In some cases, their fur has even turned a darker color, possibly as a result of their diet rich in radioactive iodine.

These dogs have learned to scavenge for food in the exclusion zone, often eating radioactive plants and animals. This has led to a higher incidence of thyroid cancer in the population.

Their remarkable resilience has allowed them to thrive in this toxic landscape, a testament to the incredible adaptability of living beings.

To collect the DNA samples, researchers took blood from 116 unique dogs, 60 from the Chernobyl Nuclear Power Plant and 56 from Chernobyl City.

These blood samples were collected during sterilization and vaccination procedures conducted by the Clean Futures Fund Dogs of Chernobyl program in 2018 and 2019.

The samples were then preserved in special tubes and transported back to the United States at a cool temperature of 0°C.

The researchers isolated genomic DNA from 500 μL of whole blood using a specific kit, following the manufacturer's instructions.

Each DNA sample was then genotyped using the Axiom Canine HD array, which yielded data for over 710,000 single nucleotide polymorphism (SNP) loci aligned to the CanFam3 genome build.

All animal protocols, handling, husbandry, and care were approved by the Columbia University Institutional Animal Care and Use Committees (IACUC).

Blood samples were collected from semi-feral dogs in two locations: around the Chernobyl Nuclear Power Plant and in Chernobyl City, 16.5 km away.

The samples were taken during sterilization and vaccination procedures conducted by the Clean Futures Fund Dogs of Chernobyl program in 2018 and 2019.

A total of 116 unique dogs were included in the study, with 60 from the Nuclear Power Plant and 56 from Chernobyl City.

Blood samples were preserved in PAXGene Blood DNA tubes and transported back to the United States for DNA extraction.

Genomic DNA was isolated from 500 μL of whole blood using the Maxwell RSC Whole Blood DNA kit according to the manufacturer’s protocol.

Each DNA sample was genotyped using the Axiom Canine HD array, yielding data for over 710,000 single nucleotide polymorphism (SNP) loci aligned to the CanFam3 genome build.

All animal protocols, handling, husbandry, and care were approved by the Columbia University Institutional Animal Care and Use Committees (IACUC).

Table 1 is a pairwise FST matrix that shows the genetic diversity between different populations. It's based on data from Pilot et al. (2015).

The matrix includes 14 populations, including Bulgaria, Poland, and China, among others. The values in the table represent the genetic distance between each pair of populations.

Here are the populations listed in the table, along with their corresponding FST values:

Two distinct populations of dogs were found to exist within the Chernobyl Exclusion Zone, one near the reactor site and another in Chernobyl City, despite being only 16 km apart.

These populations show little evidence of gene flow, indicating they have developed independently.

A genome-wide scan revealed 391 outlier loci associated with directional selection, from which 52 candidate genes were identified.

The study also analyzed the breed composition of the dogs, finding that each dog has a unique combination of breeds.

In the population near the reactor site, the average number of predominant breeds per individual was higher than in Chernobyl City.

A significant correlation was found between the number of predominant breeds and the amount of homozygosity by descent (ROH) in the dogs.

Worth a look: Dog Breeds Watch Dogs

Outlier analysis is a powerful tool used to identify genetic variations that are more common in one population than another. This study used LOSITAN to identify outlier loci associated with directional selection.

The researchers applied a higher MAF threshold to the 84 K set to highlight the strongest signals of selection and bias towards genomic regions with large effects. They also included only the 104 dogs that grouped with their capture location in the DAPC to better identify differentiating loci in each population.

The analysis ran 1,000,000 simulations and applied a 95% confidence interval and a false discovery rate of 0.1. This helps to minimize false positives and ensure that the identified loci are statistically significant.

Significant SNPs were expanded to a 10 kb genomic interval of CanFam3, and corresponding gene ontology (GO) terms were identified through the Mouse Genome Informatics Batch Query Search. This allowed the researchers to evaluate putative associations between the identified genes and environmental exposures.

The study found 391 outlier loci associated with genomic regions influenced by directional selection, from which 52 candidate genes were identified. These genes may have been affected by the unique environmental conditions faced by the dogs living near the Chernobyl Nuclear Power Plant.

Table 2 provides a wealth of information about the genetic diversity of the Nuclear Power Plant (NPP) and Chernobyl City (CC) populations.

Observed heterozygosity was significantly higher in Chernobyl City, with an average of 0.337 compared to 0.320 in the NPP population.

Expected heterozygosity was also significantly higher in Chernobyl City, with an average of 0.344 compared to 0.319 in the NPP population.

The individual inbreeding coefficients were significantly higher in Chernobyl City, with an average of 0.033 compared to 0.003 in the NPP population.

The proportion of the genome covered by ROH segments (FROH) was significantly higher in Chernobyl City, with an average of 1.02 × 10^-3 compared to 1.45 × 10^-3 in the NPP population.

Here's a summary of the key findings from Table 2:

Let's take a closer look at Table 3, which provides us with some key information about the effective population size and migration patterns of the Chernobyl City and Nuclear Power Plant populations.

The effective population size, or Θ, for Chernobyl City is estimated to be around 0.00090, with a 95% credibility interval of (0.00089, 0.00092). This means that the actual effective population size is likely to be somewhere within this range.

The effective population size for the Nuclear Power Plant is slightly higher, at 0.00096, with a 95% credibility interval of (0.00095, 0.00098).

Now let's take a look at the migration patterns between the two populations. We can see that there is a significant amount of migration from Chernobyl City to the Nuclear Power Plant, with an estimated 833.3 individuals migrating in this direction.

In contrast, the migration from the Nuclear Power Plant to Chernobyl City is estimated to be around 633.3 individuals.

Here's a quick summary of the key findings from Table 3:

These estimates give us a better understanding of the dynamics between these two populations, and can help inform our analysis of their genetic makeup.

The breed composition of dogs at Chernobyl City and Nuclear Power Plant is quite fascinating. Sixteen predominant breeds were identified, and all others contributing less than 10% were combined into a single group called 'Other Breeds'.

The populations at CC and NPP have a similar breed makeup on average, but dogs from the Nuclear Power Plant population tend to have a higher proportion of a single breed. This is evident in Supplementary Fig. 2B.

Dogs from the Nuclear Power Plant population have a higher proportion of a single breed, but this doesn't necessarily mean they have higher FROH. The number of predominant breeds in each dog is not tied to the number of ROH segments, the average size of ROH fragments, or the FROH for each individual.

There is a weak but significant positive correlation between the maximum breed score and the average size of the ROH segments, but this doesn't affect the FROH evaluation. This is why we continue to use the FROH to evaluate inbreeding.