A fast-growing population of hybrid or mutant pigs is spreading through abandoned areas near Japan’s Fukushima Daiichi Nuclear Power Plant, according to new research studying the aftermath of the 2011 nuclear disaster.

Researchers from Fukushima University and Hirosaki University analyzed DNA samples from the mutant animals and discovered that the offspring inherited key reproductive traits from domestic pigs.

The Fukushima accident was triggered after a powerful 9.0-magnitude earthquake and tsunami struck northeastern Japan in March 2011.

The disaster forced around 164,000 residents to evacuate radiation-affected areas, leaving entire towns empty for years.

An aftermath for pigs

During the chaos, domestic pigs escaped from farms and wandered into nearby forests, where they began breeding with native wild boars.

Unlike wild boars, which usually breed once a year, domestic pigs can reproduce throughout the year. Scientists say this faster reproductive cycle has allowed the hybrid population to grow rapidly inside the abandoned fallout zone.

“While it has been previously suggested that hybridization between rewilded swine and wild boars can contribute to population growth, this study demonstrates that the rapid reproductive cycle of domestic swine is inherited through the maternal lineage,” said Shingo Kaneko, a professor at the Fukushima University.

The rise of wild boars

After residents abandoned the region, wild boars quickly expanded across Fukushima’s empty farmland and forests due to lack of hunting and human activity.

The study noted that interbreeding between wild and domesticated animals is a growing global concern for wildlife management and conservation because it can disrupt natural evolutionary processes.

To better understand the hybrid pigs and their genetic traits, scientists analyzed mitochondrial DNA passed down through maternal lineages, along with nuclear genetic markers, from 191 wild boars and 10 domestic pigs collected between 2015 and 2018.

“We hypothesized that the domestic swine’s unique trait, a rapid, year-round reproductive cycle, might be the key,” co-author of the study, Dr. Donovan Anderson of Hirosaki University, said.

Researchers found that the hybrid animals showed lower levels of domestic pig DNA, inferring that repeated breeding with wild boars is slowly diluting pig genes while still preserving the fast breeding advantage.

“We wish to emphasize that this mechanism likely occurs in other regions worldwide where feral pigs and wild boars interbreed,” Hirosaki University geneticist Donovan Anderson added in a statement.

The hybrids also inherited the domestic pigs’ ability to breed more often, helping pig and wild boar genes spread faster through the population.

A stern warning

Feral swine are considered one of the world’s most destructive invasive species because they damage crops, livestock, and ecosystems.

According to the US Department of Agriculture, efforts to repair damage caused by feral swine cost an estimated $3.4 billion annually in the United States alone.

Researchers say the Fukushima case could help wildlife authorities better understand how hybrid animals spread and how quickly their populations can explode under the right conditions.

“By understanding that maternal swine lineages accelerate generation turnover, authorities can better predict population explosion risks,” Kaneko said.

The study was published in the Journal of Forest Research.