There is a growing interest in the physiology underpinning heat tolerance of ectotherms and their responses to the ongoing rise in temperature. However, there is no consensus about the underlying physiological mechanisms. According to “the maintain aerobic scope and regulate oxygen supply” hypothesis, responses to warming at different organizational levels contribute to the ability to safeguard energy metabolism via aerobic pathways. At the cellular level, a decrease in cell size increases the capacity for the uptake of resources (e.g., food and oxygen), but the maintenance of electrochemical gradients across cellular membranes implies greater energetic costs in small cells. In this study, we investigated how different rearing temperatures affected cell size and heat tolerance in the fruit fly Drosophila melanogaster. We tested the hypothesis that smaller‐celled flies are more tolerant to acute, intense heat stress whereas larger‐celled flies are more tolerant to chronic, mild heat stress. We used the thermal tolerance landscape framework, which incorporates the intensity and duration of thermal challenge. Rearing temperatures strongly affected both cell size and survival times. We found different effects of developmental plasticity on tolerance to either chronic or acute heat stress. Warm‐reared flies had both smaller cells and exhibited higher survival times under acute, intense heat stress when compared to cold‐reared flies. However, under chronic, mild heat stress, the situation was reversed and cold‐reared flies, consisting of larger cells, showed better survival. These differences in heat tolerance could have resulted from direct effects of rearing temperature or they may be mediated by the correlated changes in cell size. Notably, our results are consistent with the idea that a smaller cell size may confer tolerance to acute temperatures via enhanced oxygen supply, while a larger cell may confer greater tolerance to chronic and less intense heat stress via more efficient use of resources.

中文翻译：

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发育可塑性对耐热性的影响可能是通过果蝇细胞大小的变化介导的


人们对变温动物耐热性的生理学及其对温度持续升高的反应越来越感兴趣。然而，对于潜在的生理机制尚未达成共识。根据“维持有氧范围并调节氧气供应”的假设，不同组织层面对变暖的反应有助于通过有氧途径保障能量代谢的能力。在细胞水平上，细胞尺寸的减小增加了吸收资源（例如食物和氧气）的能力，但是细胞膜上电化学梯度的维持意味着小细胞中的能量成本更高。在这项研究中，我们研究了不同的饲养温度如何影响果蝇的细胞大小和耐热性。我们测试了这样的假设：较小细胞的果蝇更能耐受急性、强烈的热应激，而大细胞果蝇更能耐受慢性、轻度的热应激。我们使用了热耐受景观框架，其中考虑了热挑战的强度和持续时间。培养温度强烈影响细胞大小和存活时间。我们发现发育可塑性对慢性或急性热应激的耐受性有不同的影响。与冷饲养的果蝇相比，热饲养的果蝇细胞更小，在急性、强烈的热应激下表现出更长的存活时间。然而，在慢性、轻微的热应激下，情况发生了逆转，由较大细胞组成的冷饲养果蝇表现出更好的存活率。这些耐热性差异可能是由饲养温度的直接影响造成的，也可能是由细胞大小的相关变化介导的。 值得注意的是，我们的结果与这样的观点是一致的：较小的细胞尺寸可以通过增强氧气供应来赋予对急性温度的耐受性，而较大的细胞可以通过更有效地利用资源来赋予对慢性和不太强烈的热应激更大的耐受性。