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.

物种对全球变暖的易感程度，取决于其耐热性通过可塑性或进化过程响应温度升高的方式。气候适应能力可通过考察热相关性状的地理变异进行评估。我们在两种温度下饲养暗果蝇（Drosophila subobscura），以此研究其耐热性的纬度格局。我们设置4种静态热胁迫温度以估算热致死时间曲线（TDT），并开展了分别以快速和慢速升温的两种梯度升温测定实验。热致死时间曲线可通过外推至几乎可瞬时击倒果蝇的温度，来估算临界热极限（critical thermal maximum，CTmax），以及果蝇对逐步升高的热胁迫温度的热敏感性。我们发现，临界热极限（CTmax）呈现正向纬度梯度格局，但通过升温速率实验估算得到的击倒温度则无明显纬度渐变模式。尽管高纬度种群对急性热胁迫的耐受性更强，但它们对长时间暴露于轻度热胁迫环境的敏感性也更高，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，发育可塑性并不会影响临界热极限（CTmax），但可提升果蝇对慢性热胁迫的耐受性。通过热致死时间曲线得到的上述格局，有助于解释为何耐热性与纬度之间的关联会因所采用的实验方法而异；因此，这类曲线可为耐热性测定提供更为全面且可靠的量化方式。