Pig and boar hybrids surprised scientists after nuclear power plant accident

After the Fukushima Daiichi accident in 2011, some domestic pigs found themselves on the loose: due to the evacuation of people, the animals got out of their farms and started living in abandoned fields and forests. There they interbred with wild boars. This situation was a rare example of large-scale hybridisation, with almost no repeated 'feeding' by humans - and gave scientists the opportunity to track how population genetics change in real time.

The team led by Professor Shingo Kaneko (Fukushima University) came to an unexpected conclusion: the maternal line of the domestic pig did not fix the "pig" admixture, but instead accelerated the change of generations - and because of this, the share of domestic pig genes in the hybrids declined faster. The study is published online in the Journal of Forest Research on 22 January 2026.

The explanation is this. Domestic pigs tend to breed more frequently and can produce offspring all year round, whereas wild boars tend to breed seasonally - about once a year. According to the authors, the "fast" reproductive mode was passed on to offspring through the maternal line. As a result, generations in some of the hybrids changed faster, and in repeated crosses with wild boars there was an accelerated "dilution" of pig genes in nuclear DNA.

To test the hypothesis, the researchers compared mitochondrial DNA (it is inherited from the mother) and nuclear genetic markers. They examined samples from 191 wild boar and 10 domestic pigs collected between 2015 and 2018, and used population genetics models to estimate how many generations had passed since hybridisation began and how much "domestic" ancestry had been retained.

The result was counterintuitive: animals that carried domestic pig mitochondria (i.e. had a "pig mum" in their pedigree) had a lower proportion of porcine nuclear genes than hybrids with a wild boar maternal line. In many of the individuals with a "pig" maternal line, the scientists saw signs that they were already more than five generations from the original cross - indicating an unusually fast turnover of generations.

The authors emphasise that the conditions at Fukushima were exceptional: a sharp decline in human activity helped the boars to rapidly expand their numbers and range, and "accelerated maternal reproduction" may have further influenced the rate of genetic change. However, the researchers believe that the mechanism itself may also play out in other countries - wherever feral pigs and wild boars cross paths.

This is important for services dealing with invasive populations: understanding the role of maternal lines can help to better predict the risk of 'explosive' growth and prioritise control.