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交互作用是生态风险评估面临的重大挑战，在全球变暖的背景下这一问题尤为突出。尽管热适应进化或许能够提升生物应对变暖的能力，但目前尚不清楚其是否会同时影响生物应对更多在高温下毒性更强的污染物的能力。本研究借助复活生态学（resurrection ecology）手段，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进化如何改变变暖与新型胁迫因子——氧化锌纳米颗粒（nZnO）之间的交互作用。我们从某湖泊沉积物中孵化得到两个大型溞亚种群：历史祖先亚种群（1955-1965年）和近代衍生亚种群（1995-2005年）；该湖泊历史上平均水温持续上升、热浪频发，但从未接触过工业废弃物。在20℃环境下，暴露于亚致死浓度的nZnO并未对历史祖先亚种群产生显著影响；而在24℃环境中，该亚种群的内禀增长率、代谢活性与能量储备均因nZnO暴露出现下降，表明变暖与nZnO之间存在协同毒性效应。与之相反，近代衍生亚种群在24℃下对nZnO的敏感性显著降低，此类协同效应完全消失，这意味着热适应进化能够抵消变暖环境下nZnO毒性的升高。进一步分析表明，这种变暖环境下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的表达进化相关。本研究结果显示，到本世纪末预计将出现的4℃变暖环境下，大型溞种群对nZnO亚致死浓度的敏感性升高现象，可通过热适应进化得到抵消。本研究同时阐明，针对变暖的进化过程在塑造生物对另一人为胁迫因子（此处为污染物）的响应中具有重要意义。从更广泛的角度来看，对某一环境胁迫因子的遗传适应，或可消除污染物与该环境胁迫因子之间的协同交互作用。