Department of Zoology, University of British Columbia, #4200 - 6270, University Blvd, Vancouver, BC, V6T 1Z4, Canada.
Department of Zoology, University of British Columbia, #4200 - 6270, University Blvd, Vancouver, BC, V6T 1Z4, Canada; Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
J Therm Biol. 2021 Jan;95:102816. doi: 10.1016/j.jtherbio.2020.102816. Epub 2020 Dec 14.
Increasing heart rate (ƒ) is a central, if not primary mechanism used by fishes to support their elevated tissue oxygen consumption during acute warming. Thermal acclimation can adjust this acute response to improve cardiac performance and heat tolerance under the prevailing temperatures. We predict that such acclimation will be particularly important in regions undergoing rapid environmental change such as the Arctic. Therefore, we acclimated Arctic char (Salvelinus alpinus), a high latitude, cold-adapted salmonid, to ecologically relevant temperatures (2, 6, 10, 14 and 18 °C) and examined how thermal acclimation influenced their cardiac heat tolerance by measuring the maximum heart rate (ƒ) response to acute warming. As expected, acute warming increased ƒ in all Arctic char before ƒ reached a peak and then became arrhythmic. The peak ƒ, and the temperature at which peak ƒ (T) and that at which arrhythmia first occurred (T) all increased progressively (+33%, 49% and 35%, respectively) with acclimation temperature from 2 to 14 °C. When compared at the same test temperature ƒ also decreased by as much as 29% with increasing acclimation temperature, indicating significant thermal compensation. The upper temperature at which fish first lost their equilibrium (critical thermal maximum: CT) also increased with acclimation temperature, albeit to a lesser extent (+11%). Importantly, Arctic char experienced mortality after several weeks of acclimation at 18 °C and survivors did not have elevated cardiac thermal tolerance. Collectively, these findings suggest that if wild Arctic char have access to suitable temperatures (<18 °C) for a sufficient duration, warm acclimation can potentially mitigate some of the cardiorespiratory impairments previously documented during acute heat exposure.
心率（ƒ）的增加是鱼类在急性升温期间支持其升高的组织耗氧量的核心机制，如果不是主要机制。热驯化可以调整这种急性反应，以提高在流行温度下的心脏性能和耐热性。我们预测，这种驯化在经历快速环境变化的地区（如北极）将特别重要。因此，我们驯化了北极红点鲑（Salvelinus alpinus），这是一种高纬度、耐寒的鲑鱼，适应于生态相关的温度（2、6、10、14 和 18°C），并通过测量最大心率（ƒ）对急性升温的反应来研究热驯化如何影响其心脏耐热性。正如预期的那样，急性升温增加了所有北极红点鲑的ƒ，直到ƒ达到峰值，然后变得心律失常。峰值ƒ，以及达到峰值ƒ的温度（T）和首次出现心律失常的温度（T）都随着驯化温度从 2°C 到 14°C 逐渐增加（分别增加 33%、49%和 35%）。当在相同的测试温度下进行比较时，ƒ也随着驯化温度的升高而降低了 29%，表明存在显著的热补偿。鱼类首次失去平衡的上限温度（临界热最大值：CT）也随着驯化温度的升高而升高，尽管幅度较小（增加 11%）。重要的是，北极红点鲑在 18°C 下适应数周后会死亡，而幸存者的心脏耐热性并没有提高。总的来说，这些发现表明，如果野生北极红点鲑有足够长的时间接触到合适的温度（<18°C），那么温暖的驯化可能会减轻以前在急性热暴露期间记录到的一些心肺损伤。
