Bernal Diego, Donley Jeanine M, Shadwick Robert E, Syme Douglas A
Department of Biology, University of Massachusetts, Dartmouth, North Dartmouth, Massachusetts 02747, USA.
Nature. 2005 Oct 27;437(7063):1349-52. doi: 10.1038/nature04007.
Effects of temperature on muscle contraction and powering movement are profound, outwardly obvious, and of great consequence to survival. To cope with the effects of environmental temperature fluctuations, endothermic birds and mammals maintain a relatively warm and constant body temperature, whereas most fishes and other vertebrates are ectothermic and conform to their thermal niche, compromising performance at colder temperatures. However, within the fishes the tunas and lamnid sharks deviate from the ectothermic strategy, maintaining elevated core body temperatures that presumably confer physiological advantages for their roles as fast and continuously swimming pelagic predators. Here we show that the salmon shark, a lamnid inhabiting cold, north Pacific waters, has become so specialized for endothermy that its red, aerobic, locomotor muscles, which power continuous swimming, seem mammal-like, functioning only within a markedly elevated temperature range (20-30 degrees C). These muscles are ineffectual if exposed to the cool water temperatures, and when warmed even 10 degrees C above ambient they still produce only 25-50% of the power produced at 26 degrees C. In contrast, the white muscles, powering burst swimming, do not show such a marked thermal dependence and work well across a wide range of temperatures.
温度对肌肉收缩及驱动运动的影响是深远的、外在明显的，且对生存至关重要。为应对环境温度波动的影响，恒温的鸟类和哺乳动物维持相对温暖且恒定的体温，而大多数鱼类和其他脊椎动物是变温动物，顺应其热生态位，在较冷温度下性能会受到影响。然而，在鱼类中，金枪鱼和鼠鲨偏离了变温策略，维持较高的核心体温，这大概为它们作为快速持续游动的远洋捕食者的角色赋予了生理优势。我们在此表明，生活在寒冷北太平洋水域的鼠鲨科成员鲑鲨，已经高度特化适应了内温性，其为持续游泳提供动力的红色有氧运动肌肉，看起来类似哺乳动物的肌肉，仅在显著升高的温度范围（20 - 30摄氏度）内发挥作用。如果暴露在凉爽的水温中，这些肌肉就无法有效工作，即便比环境温度高出10摄氏度，它们产生的功率仍仅为26摄氏度时的25% - 50%。相比之下，为爆发式游泳提供动力的白色肌肉，并未表现出如此明显的热依赖性，能在很宽的温度范围内良好工作。
