Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
Department of Botany, University of British Columbia, Vancouver, BC, Canada.
J Anim Ecol. 2019 Dec;88(12):1901-1912. doi: 10.1111/1365-2656.13077. Epub 2019 Sep 18.
Thermal performance curves (TPCs) have been estimated in multiple ectotherm species to understand their thermal plasticity and adaptation and to predict the effect of global warming. However, TPCs are typically assessed under constant temperature regimes, so their reliability for predicting thermal responses in the wild where temperature fluctuates diurnally and seasonally remains poorly documented. Here, we use distant latitudinal populations of five species of sepsid flies (Diptera: Sepsidae) from the temperate region (Europe, North Africa, North America) to compare estimates derived from constant TPCs with observed development rate under fluctuating temperatures in laboratory and field conditions. TPCs changed across gradients in that flies originating from higher latitudes showed accelerated development at higher temperatures, an adaptive response. TPCs were then used to predict development rates observed under fluctuating temperatures; these predictions were relatively accurate in the laboratory but not the field. Interestingly, the precision of TPC predictions depended not only on the resolution of temperature data, with daily and overall temperature summing performing better than hourly temperature summing, but also on the frequency of temperatures falling below the estimated critical minimum temperature. Hourly temperature resolution most strongly underestimated actual development rates, because flies apparently either did not stop growing when temperatures dropped below this threshold, or they sped up their growth when the temperature rose again, thus most severely reflecting this error. We conclude that when flies do not encounter cold temperatures, TPC predictions based on constant temperatures can accurately reflect performance under fluctuating temperatures if adequately adjusted for nonlinearities, but when encountering cold temperatures, this method is more error-prone. Our study emphasizes the importance of the resolution of temperature data and cold temperatures in shaping thermal reaction norms.
热性能曲线（TPCs）已在多种变温动物物种中进行估算，以了解它们的热塑性和适应性，并预测全球变暖的影响。然而，TPCs 通常在恒温条件下进行评估，因此它们在预测温度波动的野外热反应方面的可靠性仍然记录不佳，温度在昼夜和季节性波动。在这里，我们使用来自温带地区（欧洲、北非、北美）的五种 sepsid 蝇种（双翅目：Sepsidae）的遥远纬度种群，将从恒温 TPC 得出的估计值与实验室和野外条件下波动温度下观察到的发育率进行比较。TPCs 随梯度变化而变化，即来自较高纬度的苍蝇在较高温度下表现出加速发育，这是一种适应性反应。然后，TPCs 用于预测波动温度下观察到的发育率；这些预测在实验室中相对准确，但在野外则不准确。有趣的是，TPC 预测的精度不仅取决于温度数据的分辨率，日温和总温度求和的效果优于小时温度求和，而且还取决于低于估计临界最低温度的温度频率。小时温度分辨率最严重地低估了实际发育率，因为当温度低于该阈值时，苍蝇显然没有停止生长，或者当温度再次升高时，它们加速了生长，从而最严重地反映了这种误差。我们得出的结论是，如果对非线性因素进行适当调整，基于恒温的 TPC 预测可以准确反映波动温度下的表现，但是当遇到低温时，这种方法更容易出错。我们的研究强调了温度数据的分辨率和低温在塑造热反应规范方面的重要性。
