Data from: Rapid evolution of antioxidant defense in a natural population of Daphnia magna

Natural populations can cope with rapid changes in stressors by relying on sets of physiological defense mechanisms. Little is known onto what extent these physiological responses reflect plasticity and/or genetic adaptation, evolve in the same direction and result in an increased defense ability. Using resurrection ecology, we studied how a natural Daphnia magna population adjusted its antioxidant defense to ultraviolet radiation (UVR) during a period with increasing incident UVR reaching the water surface. We demonstrate rapid evolution of the induction patterns of key antioxidant enzymes under UVR exposure in the laboratory. Notably, evolutionary changes strongly differed among enzymes and mainly involved the evolution of UV-induced plasticity. While D. magna evolved a strong plastic upregulation of glutathione peroxidase under UVR, it evolved a lower plastic upregulation of glutathione S-transferase and superoxide dismutase, and a plastic downregulation of catalase. The differentially evolved antioxidant strategies were collectively equally effective in dealing with oxidative stress since they resulted in the same high levels of oxidative damage (to lipids, proteins and DNA) and lowered fitness (intrinsic growth rate) under UVR exposure. The lack of better protection against UVR may suggest that the UVR exposure did not increase between both periods. Predator-induced evolution to migrate to lower depths that occurred during the same period may have contributed to the evolved defense strategy. Our results highlight the need for a multiple trait approach when focusing on the evolution of defense mechanisms.

自然种群可借助一系列生理防御机制应对胁迫因子的快速变化。目前尚不清楚这些生理应答在多大程度上反映了可塑性（plasticity）和/或遗传适应、是否沿相同方向演化，并最终提升防御能力。本研究借助复活生态学（resurrection ecology）方法，针对紫外线辐射（ultraviolet radiation, UVR）到达水面的强度持续升高的时段，探究了自然种群的大型溞（Daphnia magna）如何调整其针对UVR的抗氧化防御机制。本研究证实，实验室条件下暴露于UVR时，关键抗氧化酶的诱导模式发生了快速演化。值得注意的是，不同抗氧化酶的演化变化存在显著差异，且主要涉及UVR诱导的可塑性演化。尽管大型溞在UVR暴露下演化出了谷胱甘肽过氧化物酶（glutathione peroxidase）的强烈可塑性上调，但对谷胱甘肽S-转移酶（glutathione S-transferase）与超氧化物歧化酶（superoxide dismutase）的可塑性上调程度更低，且对过氧化氢酶（catalase）呈现出可塑性下调。这些差异化演化出的抗氧化策略在应对氧化应激（oxidative stress）时整体效果相当：无论采取哪种策略，在UVR暴露下均会产生同等程度的氧化损伤（累及脂质、蛋白质与脱氧核糖核酸（DNA）），并降低个体适合度（内禀增长率（intrinsic growth rate））。未能演化出更优的UVR防御能力，或表明两个时段间的UVR暴露水平并未提升。同期发生的、由捕食者诱导的向更深水域迁移的演化过程，或许也对本次观测到的防御策略演化起到了推动作用。本研究结果表明，在探究防御机制的演化时，需采用多性状研究方法。