1. Regional endothermy has evolved several times in marine fishes, and two competing hypotheses are generally proposed to explain the evolutionary drivers behind this trait: thermal niche expansion and elevated cruising speeds. Evidence to support either hypothesis is equivocal, and the ecological advantages conferred by endothermy in fishes remain debated.
2. By compiling published biologging data and collecting precise speed measurements from free-swimming fishes in the wild, we directly test whether endothermic fishes encounter broader temperature ranges, swim faster or both. Our analyses avoid several complications associated with earlier tests of these hypotheses, as we use precise measurements of the thermal experience and speed of individual fish.
3. Phylogenetically-informed analyses of 89 studies reporting temperature ranges encountered by tagged fishes reveal that endotherms do not encounter broader temperature ranges than their ectothermic counterparts. In contrast, speed measurements from 45 individuals (16 species, of which four were regional endotherms) show that endothermic fishes cruise ~1.6 times faster than ectotherms, after accounting for the influence of body temperature and body mass on speed.
4. Our study shows that regionally endothermic fishes—those with the ability to conserve metabolically derived heat through vascular countercurrent heat exchangers and elevate the temperature of internal tissues—swim at elevated cruising speeds, although not as fast as previously thought. Contrary to previous studies of endothermy's role in thermal niche expansion, our results suggest the significance of endothermy in fishes lies in the advantages it confers to swimming performance rather than facilitating the occupation of broader thermal niches. Given speed's major influence on metabolic rate, our updated speed estimates imply endotherms have lower routine energy requirements than current estimates.
5. Our findings shed light on the evolutionary drivers of regional endothermy in fishes and question the view that the trait confers resilience to climate change through broader thermal tolerance than that of ectotherms.

中文翻译：

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吸热使鱼更快，但不会扩大它们的热生态位

1. 区域吸热在海洋鱼类中已经进化了几次，通常提出两个相互竞争的假设来解释这一特征背后的进化驱动因素：热生态位扩张和巡航速度提高。支持这两种假设的证据是模棱两可的，鱼类吸热所带来的生态优势仍然存在争议。
2. 通过汇编已发表的生物记录数据并收集野外自由游动鱼类的精确速度测量值，我们直接测试吸热鱼类是否遇到更宽的温度范围、游得更快或两者兼而有之。我们的分析避免了与这些假设的早期测试相关的一些并发症，因为我们使用对单个鱼的热体验和速度的精确测量。
3. 对 89 项报告标记鱼遇到的温度范围的研究进行的系统发育知情分析表明，吸热鱼不会遇到比它们的变温鱼更宽的温度范围。相比之下，对 45 只个体（16 种，其中 4 种是区域性吸热鱼）的速度测量表明，在考虑了体温和体重对速度的影响后，吸热鱼的巡航速度比变温鱼快 1.6 倍。
4. 我们的研究表明，区域性吸热鱼类——那些能够通过血管逆流换热器保存代谢产生的热量并提高内部组织温度的鱼类——以较高的巡航速度游泳，尽管没有以前认为的那么快。与之前对吸热在热生态位扩张中的作用的研究相反，我们的结果表明，鱼类吸热的重要性在于它赋予游泳性能的优势，而不是促进占据更广泛的热生态位。鉴于速度对代谢率的主要影响，我们更新的速度估计意味着吸热动物的日常能量需求低于当前估计值。
5. 我们的研究结果阐明了鱼类区域恒温的进化驱动因素，并质疑这种特性通过比外温动物更广泛的热耐受性赋予气候变化适应能力的观点。