Data from: Elevated mitochondrial genome variation after 50 generations of radiation exposure in a wild rodent

Currently, the effects of chronic, continuous low dose environmental irradiation on the mitochondrial genome of resident small mammals are unknown. Using the bank vole (Myodes glareolus) as a model system, we tested the hypothesis that approximately 50 generations of exposure to the Chernobyl environment has significantly altered genetic diversity of the mitochondrial genome. Using deep sequencing, we compared mitochondrial genomes from 131 individuals from reference sites with radioactive contamination comparable to that present in Northern Ukraine before the April 26, 1986 meltdown, to populations where substantial fallout was deposited following the nuclear accident. Population genetic variables revealed significant differences among populations from contaminated and uncontaminated localities. Therefore, we rejected the null hypothesis of no significant genetic effect from 50 generations of exposure to the environment created by the Chernobyl meltdown. Samples from contaminated localities exhibited significantly higher numbers of haplotypes and polymorphic loci, elevated genetic diversity, and a significantly higher average number of substitutions-per-site across mitochondrial gene regions. Observed genetic variation was dominated by synonymous mutations, which may indicate a history of purify selection against nonsynonymous or insertion/deletion mutations. These significant differences were not attributable to sample size artifacts. The observed increase in mitochondrial genomic diversity in voles from radioactive sites is consistent with the possibility that chronic, continuous irradiation resulting from the Chernobyl disaster has produced an accelerated mutation rate in this species over the last 25 years. Our results, being the first to demonstrate this phenomenon in a wild mammalian species, are important for understanding genetic consequences of exposure to low-dose radiation sources.

目前，长期持续低剂量环境辐射对栖息于切尔诺贝利区域的小型哺乳动物线粒体基因组（mitochondrial genome）的影响尚不明确。本研究以红背䶄（bank vole, Myodes glareolus）为实验模型，检验了如下假说：在切尔诺贝利环境中暴露约50代后，线粒体基因组的遗传多样性已发生显著改变。本研究采用深度测序（deep sequencing）技术，对采自两类样地的131只个体的线粒体基因组进行比对：一类样地的辐射污染水平与1986年4月26日乌克兰北部切尔诺贝利核事故前的本底辐射水平相当，即参考对照样地；另一类则为核事故后有大量放射性沉降物沉积的受污染样地种群。群体遗传学（population genetics）分析指标显示，受污染样地与未受污染样地的种群间存在显著遗传差异。因此，我们拒绝了原假设（null hypothesis）——即在切尔诺贝利核事故造成的环境中暴露50代不会产生显著遗传效应的原假设。受污染样地的样本表现出显著更多的单倍型（haplotype）数量与多态位点（polymorphic locus）数目、更高的遗传多样性，以及线粒体基因区域内平均每位点替换数显著升高的特征。观测到的遗传变异以同义突变（synonymous mutation）为主，这或许表明该种群长期处于针对错义突变（nonsynonymous mutation）或插入缺失突变（insertion/deletion mutation）的纯化选择（purifying selection）压力之下。上述显著差异并非由样本量偏差所导致。辐射样地内红背䶄的线粒体基因组多样性升高这一观测结果，与切尔诺贝利灾难引发的长期持续辐射暴露在过去25年间加速了该物种突变率的假说相符。本研究首次在野生哺乳动物中证实了这一现象，其研究结果对于理解低剂量辐射暴露的遗传效应具有重要意义。