Data from: Thermal evolution offsets the elevated toxicity of a contaminant under warming: a resurrection study in Daphnia magna

Synergistic interactions between temperature and contaminants are a major challenge for ecological risk assessment, especially under global warming. While thermal evolution may increase the ability to deal with warming, it is unknown whether it may also affect the ability to deal with the many contaminants that are more toxic at higher temperatures. We investigated how evolution of genetic adaptation to warming affected the interactions between warming and a novel stressor: zinc oxide nanoparticles (nZnO) in a natural population of Daphnia magna using resurrection ecology. We hatched resting eggs from two D. magna subpopulations (old: 1955-1965, recent: 1995-2005) from the sediment of a lake that experienced an increase in average temperature and in recurrence of heat waves but was never exposed to industrial waste. In the old ‘ancestral’ subpopulation, exposure to a sublethal concentration of nZnO decreased the intrinsic growth rate, metabolic activity and energy reserves at 24°C but not at 20°C, indicating a synergism between warming and nZnO. In contrast, these synergistic effects disappeared in the recent ‘derived’ subpopulation that evolved a lower sensitivity to nZnO at 24°C, which indicates that thermal evolution could offset the elevated toxicity of nZnO under warming. This evolution of reduced sensitivity to nZnO under warming could not be explained by changes in the total internal zinc accumulation but was partially associated with the evolution of the expression of a key metal detoxification gene under warming. Our results suggest that the increased sensitivity to the sublethal concentration of nZnO under the predicted 4°C warming by the end of this century may be counteracted by thermal evolution in this D. magna population. Our results illustrate the importance of evolution to warming in shaping the responses to another anthropogenic stressor, here a contaminant. More general, genetic adaptation to an environmental stressor may ensure that synergistic effects between contaminants and this environmental stressor will not be present anymore.

温度与污染物之间的协同相互作用是生态风险评估（ecological risk assessment）面临的核心挑战之一，在全球变暖（global warming）的背景下这一问题尤为突出。尽管热适应性进化（thermal evolution）可提升生物应对变暖的能力，但目前尚不明确其是否会同时影响生物应对更多在高温下毒性增强的污染物的能力。本研究依托复活生态学（resurrection ecology）方法，以大型溞（Daphnia magna）的自然种群为研究对象，探究了适应变暖的遗传适应性进化如何改变变暖与新型胁迫因子——氧化锌纳米颗粒（zinc oxide nanoparticles, nZnO）之间的相互作用。我们从某一曾经历平均水温上升与热浪频发、但从未接触过工业废弃物的湖泊沉积物中，获取了两个大型溞亚种群的休眠卵：历史亚种群（1955-1965年）与近代亚种群（1995-2005年）。在24℃环境下，对历史‘祖先’亚种群施加亚致死浓度（sublethal concentration）的nZnO后，其个体的内禀增长率（intrinsic growth rate）、代谢活性（metabolic activity）与能量储备（energy reserves）均出现显著下降，但在20℃环境下未观察到此现象，表明变暖与nZnO之间存在协同效应（synergism）。与之相反，近代‘衍生’亚种群并未表现出此类协同效应：该种群在24℃下对nZnO的敏感性有所降低，这意味着热适应性进化可抵消变暖条件下nZnO毒性的增强。这种变暖条件下对nZnO敏感性降低的进化现象，无法通过体内总锌积累量的变化来解释，但部分与变暖条件下关键金属解毒基因（metal detoxification gene）的表达进化相关。本研究结果表明，到本世纪末预计的4℃变暖环境中，nZnO亚致死浓度所引发的敏感性提升效应，可被该大型溞种群的热适应性进化所抵消。同时，本研究阐明了针对变暖的适应性进化，在塑造生物对另一人为胁迫因子（anthropogenic stressor）的响应过程中所具有的重要意义。总体而言，对某一环境胁迫因子的遗传适应性进化，或可彻底消除污染物与该环境胁迫因子之间的协同效应。