Mitochondrial Genetic Mutations in the Pale Grass Blue Butterfly: Possible DNA Damage via the Fukushima Nuclear Accident and Real-Time Molecular Evolution

The pale grass blue butterfly Zizeeria maha has been used to evaluate the biological effects of the Fukushima nuclear accident in 2011. Here, we examined the DNA sequences of the mitochondrial gene cytochrome oxidase subunit I (COI) of Z. maha using the field samples collected in 2011–2014 and 2021. Among 641 individuals from 44 localities in Northeastern Japan, we detected a heteroplasmic nonsynonymous nucleotide substitution in one out of three 2012 individuals from Hirono, Fukushima Prefecture, where the biological impact of radioactive pollution was the highest among the localities surveyed in 2012, suggesting DNA damage via initial exposure to short-lived radionuclides. An additional 80 individuals from Hirono in 2021 did not show any substitution, suggesting the extinction of the Hirono mutant by 2021. We also detected another heteroplasmic and homoplasmic nonsynonymous substitution in four out of five 2014 individuals from Shibata, Niigata Prefecture, where radioactive pollution was low. These substitutions were not present in the GenBank records of Z. maha and its sister species Z. karsandra, indicating that intraspecific variation may exceed interspecific variation in Z. maha. These results highlight not only the possible impact of the initial exposure in Fukushima but also real-time molecular evolution of butterflies in the field.