Nicotinamide nucleotide and adenylate concentrations in mante, siphon and gill tissue of old and young Laternula elliptica individuals under control and experimental conditions

Future oceans are predicted to contain less oxygen than at present. This is because oxygen is less soluble in warmer water and predicted stratification will reduce mixing. Hypoxia in marine environments is thus likely to become more widespread in marine environments and understanding species-responses is important to predicting future impacts on biodiversity. This study used a tractable model, the Antarctic clam, Laternula elliptica, which can live for 36 years, and has a well-characterized ecology and physiology to understand responses to hypoxia and how the effect varied with age. Younger animals had a higher condition index, higher adenylate energy charge and transcriptional profiling indicated that they were physically active in their response to hypoxia, whereas older animals were more sedentary, with higher levels of oxidative damage and apoptosis in the gills. These effects could be attributed, in part, to age-related tissue scaling; older animals had proportionally less contractile muscle mass and smaller gills and foot compared with younger animals, with consequential effects on the whole-animal physiological response. The data here emphasize the importance of including age effects, as large mature individuals appear to be less able to resist hypoxic conditions and this is the size range that is the major contributor to future generations. Thus, the increased prevalence of hypoxia in future oceans may have marked effects on benthic organisms' abilities to persist and this is especially so for long-lived species when predicting responses to environmental perturbation.

预计未来海洋的含氧量将低于当前水平。这是因为氧气在暖水中的溶解度更低，且预计的水体层化作用会削弱水体混合。因此海洋缺氧（hypoxia）现象或将愈发普遍，而厘清物种对低氧的响应机制，对预测其对海洋生物多样性的未来影响至关重要。本研究选取了一种易于开展实验的模式物种——南极蛤（Laternula elliptica），该物种寿命可达36年，其生态学与生理学特征均已得到充分解析，以探究其对低氧的响应，以及低氧胁迫的影响如何随年龄发生变化。幼体个体的条件指数（condition index）与腺苷酸能荷（adenylate energy charge）均更高，转录谱分析显示其对低氧的响应更为活跃；而成体个体则更为静息，其鳃组织中的氧化损伤与细胞凋亡（apoptosis）水平显著升高。上述差异部分可归因于年龄相关的组织比例变化：与幼体相比，成体的收缩肌肉质量占比更低，鳃与足的尺寸更小，进而对个体整体的生理响应产生连带影响。本研究数据凸显了纳入年龄因素的重要性：大型成熟个体似乎更难以抵御低氧环境，而这类个体正是种群后续世代的主要亲本贡献者。因此，未来海洋中低氧现象愈发普遍的趋势，可能会对底栖生物的生存能力造成显著影响，在预测物种对环境扰动的响应时，长寿命物种尤其需要重点关注这一效应。