Critical thermal limits are important ecological parameters for studying thermal biology and for modelling species' distributions under current and changing climatic conditions (including predicting the risk of extinction for species from future warming). However, estimates of the critical thermal limits are biased by the choice of assay and assay conditions, which differ among studies. Furthermore, estimates of the potential for phenotypic plasticity (thermal acclimation) to buffer against thermal variability are usually based on single assay conditions and (usually linear) extrapolation from a few acclimation temperatures. We produced high resolution estimates of adult acclimation capacity for upper tolerance limits at different assay conditions (ramping rates and knock-down temperatures) using CTmax (dynamic) and knock-down (static) thermal assays in the model species Drosophila melanogaster. We found the reaction norms to be highly dependent on assay conditions. We confirmed that progressively lower ramping rates or higher knock-down temperatures led to overall lower tolerance estimates. More surprisingly, extended assays (lower ramping rates or lower knock-down temperatures) also led to increasingly non-linear reaction norms for upper thermal tolerance across adult acclimation temperatures. Our results suggest that the magnitude (capacity) and direction (beneficial or detrimental) of acclimation responses are highly sensitive to assay conditions. The results offer a framework for comparison of acclimation responses between different assay conditions and a potential for explaining disparate acclimation capacity theories. We advocate cautious interpretation of acclimation capacities and careful consideration of assay conditions, which should represent realistic environmental conditions based on species' ecological niches.

中文翻译：

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测试温度极限：非线性反应规范在果蝇中驱动不同的热适应反应。

临界热极限是重要的生态参数，对于研究热生物学以及模拟当前和不断变化的气候条件下的物种分布（包括预测未来变暖导致物种灭绝的风险）是重要的生态参数。但是，临界热极限的估计值因检测方法和检测条件的选择而有偏差，这在研究之间有所不同。此外，对表型可塑性（热适应）缓冲以抵抗热变异性的潜力的估算通​​常基于单个测定条件和从几个适应温度进行的（通常为线性）推断。我们使用模型种果蝇（Drosophila melanogaster）中的CTmax（动态）和组合式（静态）热分析方法，在不同的分析条件（爬升速率和组合式温度）下，对成年驯化能力的上限进行了高分辨率估计。我们发现反应规范高度依赖于测定条件。我们确认，逐渐降低的升温速率或较高的组合温度导致总体上较低的耐受性估计。更令人惊讶的是，扩展的检测方法（较低的升温速率或较低的敲除温度）也导致了在成年适应温度下对较高热耐受性的非线性反应标准越来越多。我们的结果表明，适应反应的幅度（容量）和方向（有益或有害）对测定条件高度敏感。结果提供了一个框架，用于比较不同测定条件之间的适应性反应以及解释不同适应性能力理论的潜力。我们提倡对适应能力的谨慎解释，并仔细考虑测定条件，这些条件应代表基于物种生态位的现实环境条件。