In Chernobyl, two groups of dogs living a few kilometres apart have remarkably different DNA.
Since the 1986 nuclear accident, stray dogs have lived in the abandoned area around the Ukrainian power plant. Some live near the facilities, while others live in the city of Chernobyl, about 16 km away. Studies had already shown that these two populations were genetically distinct. New research seeks to understand why, without automatically attributing this difference to radioactivity.
A brown-and-black dog sitting in a grassy area in Chernobyl, in November 2017.
Credit: Jorge Franganillo, CC BY 2.0.
To investigate further, the researchers revisited genetic data collected from 106 dogs in 2018 and 2019. Their DNA contains a multitude of small variations inherited from their parents. By comparing their frequency from one group to the other, the team sought to determine what could explain such a marked separation.
One possible explanation would have been the appearance of numerous new mutations caused by radiation. However, previous studies had not found an increase in mutations sufficient to explain this gap. The researchers therefore examined two other possibilities: chance and natural selection.
Chance can alter the frequency of certain genetic variants in a small, isolated population. To test this, the research team notably studied dogs living in the Galápagos Islands. Despite their geographic isolation, their genetic differences did not resemble those observed near the power plant. Chance therefore does not appear sufficient to explain the result.
The researchers identified more than one hundred regions of DNA showing signs of natural selection. This mechanism can favour, over the course of generations, characteristics already present in some animals. If these characteristics help them survive better or reproduce more, their carriers may pass these variants on to their offspring more often.
Several of the identified regions are located near genes associated with DNA repair, defences against infections and cell function. The researchers identified genetic differences, but have not yet demonstrated their concrete effects on the animals’ health.
Radioactivity is also not the only factor present in this area. The environment has also been contaminated by heavy metals and other chemical substances. It would therefore be premature to attribute the observed differences solely to radiation. The genetic evidence supports the hypothesis of selection, without providing direct proof of it.
One possibility is that some dogs already possessed variants that were advantageous in this environment. Over the course of generations, their descendants may have become more numerous.