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，在全球变暖背景下这一问题尤为突出。尽管热适应性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那些在高温下毒性更强的多种污染物的能力。本研究借助复活生态学（resurrection ecology）手段，以大型溞（Daphnia magna）自然种群为研究对象，探究了针对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（nZnO）之间的交互作用。我们从某湖泊的沉积物中孵化出两个大型溞亚种群的休眠卵：分别为1955-1965年的‘古老祖先亚种群’与1995-2005年的‘近代衍生亚种群’；该湖泊年均水温升高、热浪频发，但从未接触过工业废弃物。在古老祖先亚种群中，当处于24℃环境时，暴露于亚致死浓度的nZnO会降低其内禀增长率、代谢活性与能量储备，但在20℃环境下则无此现象，这表明变暖与nZnO之间存在协同效应。与之相反，近代衍生亚种群并未出现此类协同效应：该种群在24℃环境下对nZnO的敏感性有所降低，这表明热适应性进化能够抵消变暖环境下nZnO毒性的升高。变暖环境下nZnO敏感性降低的这种进化，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有关。本研究结果表明，若按照预测到本世纪末全球升温4℃的情景，大型溞种群对亚致死浓度nZnO的敏感性会有所提升，但这种提升可通过热适应性进化得到抵消。本研究结果凸显了变暖适应性进化在调控生物对另一类人为胁迫因子（即污染物）的响应过程中的重要性。从更广泛的层面来看，对某一环境胁迫因子的遗传适应性进化，或可消除污染物与该环境胁迫因子之间的协同交互效应。