After the Fukushima nuclear accident, the pigs on the farms fled into the forest. Years later they were something different

March 11, 2011 was one of the darkest days in Japan’s recent history. And probably the worst so far in the 21st century. An intense earthquake recorded off Honshu unleashed a tsunami with waves of more than ten meters that ended up precipitating an accident at the Fukushima plant. You have to go back to 1986, to Chernobyl, to find a similar incident.

Today we know that that chain of misfortunes had an unexpected consequence: it gave rise to an involuntary experiment with pigs and wild boars.

Pigs on the run. After the Fukushima Daiichi accident in March 2011, authorities rushed to evacuate all the people living in a radius of 20 kilometers of the nuclear power plant. Even those residing 20 to 30 km away were advised not to leave their homes. Today, a decade and a half later, we know that the Fukushima incident had another consequence: the pigs that until then were raised in domestic farms fled and took refuge in the forests, places that until then had served as home to wild boars.

An XXL laboratory. The escape of the Fukushima pigs (and their clash with the wild boar populations) could have remained a minor anecdote if it were not for the fact that it gave rise to a curious improvised experiment. An involuntary one, which no one had planned, but which, due to the chances of history, ended up turning the forests of the exclusion zone into a gigantic zoological laboratory. The reason? Escaped pigs and wild boars ended up mating.

“Without repeated introductions and minimal human activity, the region became a rare natural hybridization experiment,” explains Fukushima University. The experience was certainly interesting enough to attract the attention of Shingo Kaneko and Donovan Anderson, from Hirosaki, who decided to carry out a genetic study to better understand the results of crossing pigs and wild boars. Their conclusions have just been expressed in a published article a few days ago in the magazine Journal of Forest Research.

What did they find out? Perhaps the most surprising has to do with the renewal of populations. Domestic pigs and wild boars differ not only in their appearance. They also show different patterns. For example, while the latter reproduce once a year, the former, the pigs we raise on farms, show a much faster cycle throughout the year. Kaneko’s study shows that this peculiarity of domesticated animals was maintained after their escape and was transmitted during hybridization through the mother.

five generations. There is one piece of information that helps to better understand how accelerated its reproduction rate has been. For their study, the researchers analyzed the mitochondrial DNA and genetic markers of more than 200 animals captured over three years, between 2015 and 2018. One of the first questions they tried to clarify was: How related were these specimens to the pigs that escaped in 2011? How many came from that domestic lineage?

Their conclusion was surprising: many hybrids were already more than five generations away from the original cross, suggesting “unusually rapid genetic renewal.” they add from Fukushima University.

“Although it has previously been suggested that hybridization between pigs reintroduced into the wild and wild boar could contribute to population growth, this study shows, by analyzing a large-scale hybridization event following the Fukushima nuclear accident, that the rapid reproductive cycle of domestic pigs is inherited through the maternal lineage.”

A diluted inheritance. It was not the only conclusion that the experts reached. Another, just as curious, is how hybrid creatures evolved.

That domestic females favored a higher rate of reproduction does not mean that their inheritance was more pronounced. Quite the opposite. Farm sows energized generational renewal, but the initial strength of their genes was diluted little by little. “Rather than prolonging the genetic influence of domestic pigs, maternal pig lineages actually accelerated genetic turnover in wild boar populations,” apostille from Fukushima.

Why is it important? The research is not interesting only for what it reveals to us about the Fukushima exclusion zone. Their conclusions go further and have practical implications for the rest of the world. Experts have long been concerned about hybridization between domestic and wild animals (especially between pigs and wild boars) due to its ecological repercussions.

Curiously, the accident that occurred in Japan in 2011 has offered researchers a huge laboratory to better understand the phenomenon and how to address it. “The findings can be applied to wildlife management and invasive species damage control strategies,” Kaneko celebrates. “By understanding that the pig’s maternal lineage accelerates generational turnover, authorities can better predict the risks of population explosion.”

Images | Max Saeiling (Unsplash), Wikipedia and Fukushima University

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