Gene expression and physiological changes of the Antarctic krill Euphausia superba under different hypoxia intensities@en

Antarctic krill (Euphausia superba) from South Georgia comprise one of the most northern and abundant krill stocks. South Georgia waters are undergoing rapid warming, as a result of climate change, which in turn could alter the oxygen concentration of the water. We investigated gene expression in Antarctic krill related to aerobic metabolism, antioxidant defence, and heat-shock response under severe (2.5% O2 saturation or 0.6 kPa) and threshold (20% O2 saturation or 4 kPa) hypoxia exposure compared to in situ levels (normoxic; 100% O2 saturation or 21 kPa). Biochemical metabolic and oxidative stress indicators complemented the genic expression analysis to detect in vivo signs of stress during the hypoxia treatments. Expression levels of the genes citrate synthase (CS), mitochondrial manganese superoxide dismutase (SODMn-m) and one heat-shock protein isoform (E) were higher in euphausiids incubated 6 h at 20% O2 saturation than in animals exposed to control (normoxic) conditions. All biochemical antioxidant defence parameters remained unchanged among treatments. Levels of lipid peroxidation were raised after 6 h of severe hypoxia. Overall, short-term exposure to hypoxia altered mitochondrial metabolic and antioxidant capacity, but did not induce anaerobic metabolism. Antarctic krill are swarming organisms and may experience short periods of hypoxia when present in dense swarms. A future, warmer Southern ocean, where oxygen saturation levels are decreased, may result in smaller, less dense swarms as they act to avoid greater levels of hypoxia.源自南乔治亚岛的南极大磷虾（Antarctic krill, Euphausia superba）是全球分布最靠北、种群丰度最高的磷虾类群之一。受气候变化影响，南乔治亚岛周边海域正经历快速升温，进而改变海水的溶解氧水平。本研究以原位常氧条件（氧饱和度100%，即21 kPa）为对照，检测南极大磷虾在严重低氧（氧饱和度2.5%，即0.6 kPa）与临界低氧（氧饱和度20%，即4 kPa）暴露下，其与有氧代谢、抗氧化防御及热休克应答相关的基因表达情况。同时通过生化代谢与氧化应激指标补充基因表达分析结果，以检测低氧处理过程中受试个体的体内应激指征。在氧饱和度20%的条件下培养6小时后，受试磷虾的柠檬酸合酶（citrate synthase, CS）、线粒体锰超氧化物歧化酶（mitochondrial manganese superoxide dismutase, SODMn-m）以及1种热休克蛋白亚型E的表达水平，均显著高于常氧对照组。所有生化抗氧化防御指标在各组处理间均无显著变化。经6小时严重低氧处理后，受试个体的脂质过氧化水平显著升高。综合分析结果表明，短期低氧暴露可改变南极大磷虾的线粒体代谢与抗氧化能力，但未诱导其厌氧代谢途径激活。南极大磷虾为群集性生物，当形成高密度种群时，个体自身可能会短暂处于低氧环境中。在未来气候变暖的背景下，南大洋溶解氧饱和度将进一步降低，南极大磷虾为规避更高程度的低氧环境，其种群规模将趋于缩小、群集密度也会相应下降。