Variation in chronic radiation exposure does not drive life history divergence among Daphnia populations across the Chernobyl Exclusion Zone

Ionising radiation is a mutagen with known negative impacts on individual fitness. However, much less is known about how these individual fitness effects translate into population-level variation in natural environments that have experienced varying levels of radiation exposure. In this study, we sampled genotypes of the freshwater crustacean, Daphnia pulex, from the eight inhabited lakes across the Chernobyl Exclusion Zone (CEZ). Each lake has experienced very different levels of chronic radiation exposure since a nuclear power reactor exploded there over thirty years ago. The sampled Daphnia genotypes represent genetic snapshots of current populations and allowed us to examine fitness-related traits under controlled laboratory conditions at UK background dose rates. We found that whilst there was variation in survival and schedules of reproduction among populations, there was no compelling evidence that this was driven by variation in exposure to radiation. Previous studies have shown that controlled exposure to radiation at dose rates included in the range measured in the current study reduce survival, or fecundity, or both. One limitation of this study is the lack of available sites at high dose rates, and future work could test life history variation in various organisms at other high radiation areas. Our results are nevertheless consistent with the idea that other ecological factors, e.g., competition, predation or parasitism, are likely to play a much bigger role in driving variation among populations than exposure to the high radiation dose rates found in the CEZ. These findings clearly demonstrate that it is important to examine the potential negative effects of radiation across wild populations that are subject to many and varied selection pressures as a result of complex ecological interactions.

电离辐射（Ionising radiation）是一种诱变剂，已知其对个体适合度具有明确的负面影响。然而，对于这些个体适合度效应如何在经历不同辐射暴露水平的自然环境中转化为种群水平的变异，目前的研究仍较为匮乏。本研究从切尔诺贝利隔离区（Chernobyl Exclusion Zone, CEZ）内的8个已有人居住的湖泊中，采集了淡水甲壳动物蚤状溞（Daphnia pulex）的基因型样本。三十余年前，该区域一处核反应堆发生爆炸，此后各湖泊所承受的慢性辐射暴露水平均存在显著差异。所采集的蚤状溞基因型可视为当前种群的遗传快照，使我们得以在英国本底剂量率的受控实验室条件下，检测与个体适合度相关的性状。研究结果显示，尽管不同种群间的存活情况与繁殖时序存在变异，但并无确凿证据表明该变异由辐射暴露水平差异所驱动。既往研究表明，当辐射暴露剂量率处于本研究测得的范围内时，受控辐射暴露会降低受试个体的存活率、繁殖力，或同时影响两者。本研究存在一项局限：缺乏高剂量率辐射的采样位点，未来可针对其他高辐射区域的多种生物开展生活史变异相关研究。尽管如此，本研究结果仍支持以下观点：相较于切尔诺贝利隔离区内的高辐射剂量率暴露，诸如竞争、捕食或寄生等其他生态因子，在驱动种群间变异方面更可能发挥更为关键的作用。本研究结果清晰表明，针对因复杂生态相互作用而承受多样选择压力的野生种群，系统探究辐射的潜在负面影响具有重要意义。