Data from: Heat tolerance in Drosophila subobscura along a latitudinal gradient: contrasting patterns between plastic and genetic responses

Susceptibility to global warming relies on how thermal tolerances respond to increasing temperatures through plasticity or evolution. Climatic adaptation can be assessed examining the geographic variation in thermal-related traits. We studied latitudinal patterns in heat tolerance in Drosophila subobscura reared at two temperatures. We used four static stressful temperatures to estimate the thermal death time curves (TDT), and two ramping assays with fast and slow heating rates. TDT curves allow estimating the critical thermal maximum CTmax, by extrapolating to the temperature that would knockdown the flies almost ‘instantaneously’, and the thermal sensitivity to increasing stressful temperatures. We found a positive latitudinal cline for CTmax, but no clinal pattern for knockdown temperatures estimated from the ramping assays. Although high-latitude populations were more tolerant to an acute heat stress, they were also more sensitive to prolonged exposure to less stressful temperatures, supporting a trade-off between acute and chronic heat tolerances. Conversely, developmental plasticity did not affect CTmax but increased the tolerance to chronic heat exposition. The patterns observed from the TDT curves help to understand why the relationship between heat tolerance and latitude depends on the methodology used and, therefore, these curves provide a more complete and reliable measurement of heat tolerance.

生物对全球变暖的敏感性，取决于其耐热性如何通过表型可塑性或演化适应响应温度升高。气候适应可通过分析耐热相关性状的地理变异加以评估。本研究以两种温度条件下饲养的暗果蝇（Drosophila subobscura）为对象，探究其耐热性的纬度分布格局。我们采用4种静态胁迫温度拟合热死亡时间曲线（thermal death time curves，TDT），并开展了两组分别以快速与慢速升温速率的变温胁迫实验。热死亡时间曲线可通过外推至几乎“瞬时”击倒果蝇的温度，估算得到关键热极限（critical thermal maximum，CTmax）以及果蝇对胁迫温度升高的热敏感性。研究结果显示，关键热极限（CTmax）呈现正向纬度梯度格局，但通过变温升温实验测得的击倒温度则无显著纬度梯度分布模式。尽管高纬度种群对急性热胁迫的耐受性更强，但它们对低强度胁迫温度的长期暴露也更为敏感，这支持了急性与慢性耐热性之间存在权衡关系的结论。与之相反，发育可塑性并未对关键热极限（CTmax）产生影响，但提升了果蝇对慢性热胁迫的耐受性。通过热死亡时间曲线（TDT）观测到的格局，有助于解释为何耐热性与纬度之间的关联会因研究方法不同而存在差异；因此，该曲线能够为耐热性提供更为全面且可靠的测定方式。