Dissecting Oxidative Stress and Organismic Response to a Temperature Gradient in the midge Chironomus riparius

Oxidative stress, caused by reactive oxygen species (ROS), poses a major challenge for organisms facing temperature fluctuations. This study provides the first direct in vivo measurements of ROS production together with transcriptome analysis of oxidative stress genes across a broad range of ecologically relevant temperatures in insect larvae of the dipteran midge Chironomus riparius. We observed a U-shaped pattern of oxidative stress, with minimal ROS levels within an optimal thermal window (12-18°C) and significantly elevated stress at both cold and warm extremes. Crucially, our findings reveal distinct underlying molecular mechanisms for ROS generation at these extremes: at low temperatures, predominantly ROS produced is of the superoxide group, linked to hypoxia-induced hemoglobin autoxidation. Conversely, at high temperatures, the hydrogen peroxide group dominates, associated with increased metabolic rate and heat stress signaling pathways. Transcriptomic analysis shows that C. riparius's antioxidant defense system adapts accordingly, selectively upregulating mechanisms to counteract the specific dominant ROS type at different temperatures. This mechanistically differentiated oxidative stress at different temperatures and the modulated organismic response reflects the ecological niche and evolution of C. riparius.由活性氧（reactive oxygen species, ROS）诱导产生的氧化应激，是生物体遭遇温度波动时所面临的重大生存挑战。本研究首次针对双翅目摇蚊（Chironomus riparius）的幼虫，在一系列符合生态相关性的温度梯度下，直接开展了ROS生成量的体内（in vivo）检测，并对氧化应激相关基因进行了转录组分析。研究团队观察到氧化应激呈现U型分布模式：在最适温度区间（12-18℃）内ROS水平最低，而在低温和高温极端条件下应激水平均显著升高。尤为关键的是，本研究揭示了极端温度下ROS生成的截然不同的潜在分子机制：低温条件下，生成的ROS以超氧基团为主，该过程与缺氧诱导的血红蛋白自氧化反应相关；与之相反，高温条件下则以过氧化氢基团为主，该现象与代谢速率提升及热应激信号通路激活密切相关。转录组分析结果显示，摇蚊的抗氧化防御系统会做出相应适应性调整，选择性上调相关机制以抵消不同温度下占主导的特定ROS类型。这种不同温度下氧化应激的机制分化，以及生物体所做出的调控性响应，反映了摇蚊的生态位与演化历程。