Maternal lineage of rewilded swine in Fukushima contributes to faster introgression in wild boar populations

Hybridization between wild animals and escaped or abandoned domestic animals poses significant challenges for wildlife management and conservation, particularly by disrupting evolutionary processes. Large-scale events, such as the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, can lead to the release of domestic animals into the forested areas and agricultural lands abandoned after human evacuation, increasing the likelihood of hybridization or admixture with their wild relatives. This study investigates the genetic influence of domestic swine Sus scrofa domesticus on wild boar Sus scrofa leucomystax populations in the evacuation zone of Fukushima Prefecture, Japan. Using mitochondrial DNA (mtDNA) haplotypes and nuclear SSR genotypes from 191 wild boars and 10 domestic pigs collected during 2015–2018, we examined how maternal lineage relates to the proportion of domestic alleles in admixed individuals. STRUCTURE analysis with the USEPOPINFO model and GENSBACK option revealed that 21 of the 31 admixed individuals were beyond the fifth generation since hybridization. Individuals with swine-derived mtDNA haplotypes exhibited a lower proportion of swine nuclear alleles compared to those carrying wild boar haplotypes, suggesting a faster reproductive turnover in the maternal swine lineage. These results imply that the shorter reproductive cycle of domestic swine may have accelerated the dilution of swine nuclear genomes within wild boar populations following the FDNPP accident. Although the overall impact of hybridization appears limited, even small-scale genetic introgression may complicate population management.