Japanese scientists have made a significant breakthrough in understanding the genetic processes that led to the rise of radioactive pig-boar hybrids in the abandoned evacuation zone of Fukushima. This phenomenon has become a unique natural experiment, offering insights into how domestic animals can interbreed with their wild counterparts.
After the 2011 Fukushima nuclear disaster and the subsequent evacuation of residents, a small number of domestic pigs managed to escape from local farms and began to reproduce with native wild boar in the area. With no further introduction of pigs and minimal human activity, the region has turned into an ideal setting for studying the effects of hybridisation between domestic and wild animals.
Hybridisation between domestic and wild species is a growing concern globally, especially in areas where feral pigs and wild boar are increasingly overlapping. This can lead to ecological damage, but the biological mechanisms behind these changes have remained unclear.
In a recent study, geneticists from Fukushima investigated this rare occurrence and found that while the genes of domestic pigs became diluted over generations, their rapid reproductive capacity was retained in the hybrid hogs. This discovery provides new understanding about how such hybrid populations evolve.
Wild boars typically live outdoors and breed once a year, whereas domestic pigs, raised by humans, can reproduce year-round with larger litters. However, the exact way their genes mix when they interbreed is still not fully understood. Researchers collected tissue samples from 191 wild boars and 10 domestic pigs that were living in the Fukushima exclusion zone between 2015 and 2018.
They studied two types of DNA: mitochondrial DNA (mtDNA), which is inherited only from the mother, and nuclear DNA, which comes from both parents. This allowed them to track maternal ancestry separately from overall genetic mixing.
The DNA analysis also helped determine how much domestic pig genetic material remained in the hybrid population and how quickly these genes were being diluted. The researchers found that when domestic pigs bred with wild boar, their offspring carried the domestic mother’s mtDNA for around five generations. This suggests that over time, the genetic makeup of these hybrids became more like wild boar than domestic pigs, indicating that the hybrids continued to breed back with wild boar.
The findings reveal that domestic pig genes were diluted more quickly than previously thought. However, the pigs’ fast, year-round reproductive cycle persisted, with later generations becoming more similar to wild boar.
“We believe this mechanism likely occurs in other regions worldwide where feral pigs and wild boars interbreed,” said study author Donovan Anderson from Hirosaki University. “These findings can be used in wildlife management and strategies to control invasive species. By understanding that maternal swine lineages accelerate generation turnover, authorities can better predict risks of population explosions,” added Shingo Kaneko, another author of the study.
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