Predicting the effects of high environmental temperatures and drought on populations requires understanding how these conditions will influence the thermoregulatory behavior and thermal tolerance of organisms. Ectotherms show proportional (fine-tuned) and all-or-none (abrupt) responses to avoid overheating. Scattered evidence suggests that dehydration alters these behavioral responses and thermal tolerance, but these effects have not been evaluated in an integrative manner. We examined the effects of hydration level on the behavioral thermoregulation and behavioral and physiological thermal limits of the "bullfrog" (Rana catesbeiana), a well-studied and important invasive species. To examine the effects of dehydration on proportional responses, we compared the Preferred Body Temperatures (PBT) of frogs with restricted and unrestricted access to water. To assess the effect of dehydration on all-or-none responses, we measured and compared the Voluntary Thermal Maximum (VTMax) at different hydration levels (100%, 90%, 80% of body weight at complete hydration). Finally, to understand the effect of dehydration on physiological thermal tolerance, we measured the Critical Thermal Maximum (CTMax) of frogs at matched hydration levels. PBT, VTMax, and CTMax all decreased in response to higher dehydration levels. However, bullfrogs changed their PBT more than their VTMax or CTMax in response to dehydration. Moreover, some severely dehydrated individuals did not exhibit a VTMax response. We discuss the implications of our results in the context of plasticity of thermoregulatory responses and thermal limits, and its potential application to mechanistic modeling.

中文翻译：

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脱水对林蛙体温调节行为和热耐受极限的影响 (Shaw, 1802)

预测高环境温度和干旱对种群的影响需要了解这些条件将如何影响生物体的体温调节行为和热耐受性。等温线显示成比例（微调）和全有或全无（突然）响应，以避免过热。零星的证据表明，脱水会改变这些行为反应和热耐受性，但尚未以综合方式评估这些影响。我们研究了水合水平对“牛蛙”（Rana catesbeiana）的行为体温调节以及行为和生理热极限的影响，牛蛙是一种经过充分研究的重要入侵物种。为了检查脱水对比例反应的影响，我们比较了受限制和不受限制的饮水条件下青蛙的首选体温 (PBT)。为了评估脱水对全有或全无反应的影响，我们测量并比较了不同水合水平（完全水合时体重的 100%、90%、80%）的自愿热最大值 (VTMax)。最后，为了了解脱水对生理热耐受性的影响，我们测量了青蛙在匹配的水合水平下的临界热最大值 (CTMax)。PBT、VTMax 和 CTMax 都随着脱水水平的升高而降低。然而，牛蛙对脱水的反应比他们的 VTMax 或 CTMax 更能改变他们的 PBT。此外，一些严重脱水的人没有表现出 VTMax 反应。