Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1.
J Exp Biol. 2023 May 15;226(10). doi: 10.1242/jeb.245425. Epub 2023 May 18.
Climate change is leading to rapid change in aquatic environments, increasing the mean and variability of temperatures, and increasing the incidence of hypoxia. We investigated how acclimation to constant temperatures or to diel temperature fluctuations affects hypoxia tolerance in mummichog killifish (Fundulus heteroclitus). Killifish were acclimated to constant cool (15°C), constant warm (25°C) or a diel temperature cycle (15°C at night, 25°C during day) for 6 weeks. We then measured hypoxia tolerance (time to loss of equilibrium in severe hypoxia, tLOE; critical O2 tension, Pcrit), whole-animal metabolism, gill morphology, haematology and tissue metabolites at 15°C and 25°C in a full factorial design. Among constant temperature groups, tLOE was highest and Pcrit was lowest in fish tested at their acclimation temperature. Warm-acclimated fish had lower metabolic rate at 25°C and greater gill surface area (less coverage of lamellae by interlamellar cell mass, ILCM), but cool-acclimated fish had greater brain glycogen stores. Therefore, effects of constant temperature acclimation on hypoxia tolerance were temperature specific and not exhibited broadly across test temperatures, and they were associated with different underlying mechanisms. Hypoxia tolerance was less sensitive to test temperature in fish acclimated to fluctuating temperatures compared with fish acclimated to constant temperature. Acclimation to fluctuating temperatures also increased haemoglobin-O2 affinity of the blood (decreased P50) compared with constant temperature groups. Therefore, acclimation to fluctuating temperatures helps maintain hypoxia tolerance across a broader range of temperatures, and leads to some distinct physiological adjustments that are not exhibited by fish acclimated to constant temperatures.
气候变化导致水生环境迅速变化，增加了温度的平均值和变异性，并增加了缺氧的发生率。我们研究了适应恒温和昼夜温度波动如何影响花斑鲦鱼（Fundulus heteroclitus）的缺氧耐受性。花斑鲦鱼适应恒冷（15°C）、恒暖（25°C）或昼夜温度循环（夜间 15°C，白天 25°C）6 周。然后，我们在全面因子设计中测量了 15°C 和 25°C 下的缺氧耐受性（严重缺氧时失去平衡的时间，tLOE；临界 O2 张力，Pcrit）、整体动物代谢、鳃形态、血液学和组织代谢物。在恒温组中，在适应温度下测试的鱼的 tLOE 最高，Pcrit 最低。暖适应的鱼在 25°C 时的代谢率较低，而鳃表面积较大（板间细胞质量 ILCM 覆盖的鳃片较少），但冷适应的鱼大脑糖原储存较多。因此，恒温适应对缺氧耐受性的影响是特定于温度的，而不是在整个测试温度范围内表现出来的，并且与不同的潜在机制有关。与恒温适应的鱼相比，适应波动温度的鱼对缺氧的耐受性对测试温度的敏感性较低。与恒温组相比，适应波动温度还增加了血液的血红蛋白-O2 亲和力（降低了 P50）。因此，适应波动温度有助于在更宽的温度范围内维持缺氧耐受性，并导致一些恒温适应的鱼没有表现出的独特生理适应。
