Thermal stress experiments are essential for understanding organisms' thermal limits and the physiological processes that contribute to establishing those limits. Experiments typically employ either an abrupt transfer to near-lethal temperatures or a gradually increasing thermal exposure. In the current study, we used three populations of the intertidal copepod Tigriopus californicus that are known to differ in upper thermal tolerance to investigate the effects of gradual versus abrupt thermal exposures on survivorship, developmental time, and heat shock protein gene expression. The developmental rate of nauplii was unaffected following the gradual exposure, whereas developmental time slowed by ∼2 d (∼20%) following an abrupt exposure. The gradual exposure also improved survivorship in comparison to the abrupt exposure. Furthermore, the heat shock protein genes hsp70 and hspb1 showed greater upregulation during the gradual thermal exposure compared to the abrupt exposure. Though the differences in response to each thermal regime varied in magnitude among the different populations, the types of responses were very similar (i.e., following the gradual exposure survivorship increased, developmental time showed no effect, and heat shock protein gene upregulation during the exposure increased). Therefore, the enhanced protective effect of the heat shock response during gradual exposures appears to be conserved within the species despite population-level differences in thermal tolerance. Thus, an ecologically relevant thermal exposure likely enables improved cellular protective mechanisms by allowing for an effective and timely heat shock response, which plays a role in mitigating the effects of thermal stress and thereby enhances tolerance to elevated temperatures.

中文翻译：

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与生态相关的温度上升速率可增强潮间带温度下的保护性热冲击响应。

热应力实验对于理解生物体的热极限和有助于建立这些极限的生理过程至关重要。实验通常采用突然转移到接近致命温度或逐渐增加热暴露的方式。在当前的研究中，我们使用了潮间co足类Tigriopus californicus的三个种群，其在较高的热耐受性方面有所不同，以研究逐渐和突然的热暴露对存活率，发育时间和热休克蛋白基因表达的影响。逐渐暴露后，无节幼体的发育率不受影响，而突然暴露后，发育时间减慢了约2 d（约20％）。与突然暴露相比，逐渐暴露还改善了生存能力。此外，热休克蛋白基因hsp70和hspb1与逐渐暴露相比在逐渐的热暴露中表现出更大的上调。尽管不同群体对每种热机制的反应差异在大小上有所不同，但反应的类型却非常相似（即，随着逐渐暴露的存活率增加，发育时间没有影响，并且暴露期间的热休克蛋白基因上调增加）。因此，尽管种群之间在热耐受性方面存在差异，但是在逐渐暴露过程中，热休克反应的增强保护作用似乎在物种内得以保留。因此，与生态相关的热暴露可能会通过允许有效及时的热休克反应来改善细胞保护机制，