Spatiotemporal Dynamics of Genetic Diversity in the Pale Grass Blue Butterfly After the Fukushima Nuclear Accident

The Fukushima nuclear accident in 2011 caused adverse phenotypic changes in wild organisms in radioactively polluted areas. However, few studies have investigated genetic changes after the accident. Here, we analyzed the nuclear DNA sequences of internal transcribed spacer 2 (ITS2) from the pale grass blue butterfly Zizeeria maha collected in 2011–2014 (n = 389). We detected 29 haplotypes, but the most frequent haplotype (H1) represented 86% of alleles examined. The haplotype H22 from Takahagi phylogenetically had the latest sequence, suggesting that it may be a novel mutant produced by the accident or just a minor existing haplotype. In Fukushima Prefecture, the H1 percentage oscillated; it peaked in Fall 2011 and decreased in Spring 2012 but peaked again in Fall 2012. Haplotype diversity and nucleotide diversity were low in Spring 2012 and Fall 2012 and then increased. The ratio of H1 to nonH1 was significantly different between the early and late periods of our field surveys. These results suggest that genetic diversity in Fukushima Prefecture initially decreased through a selection process in response to the Fukushima nuclear accident but was recovered by Fall 2014, probably due to immigrants and emerging mutants, which is consistent with previous morphological abnormality data.