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，取决于热耐受性（thermal tolerance）如何通过表型可塑性或进化过程响应温度升高。气候适应性可通过分析与热相关性状的地理变异进行评估。我们在两种温度条件下饲养暗果蝇（Drosophila subobscura），研究其耐热性的纬度分布格局。我们采用4种静态胁迫温度以估算热致死时间曲线（TDT），并设置了2组分别以快速和慢速升温的升温试验。热致死时间曲线（TDT）可通过外推至几乎“瞬时”击倒果蝇的温度，来估算临界热最大值（CTmax）以及生物对升高的胁迫温度的热敏感性。我们发现临界热最大值（CTmax）呈现正向纬度梯度，但通过升温试验估算得到的击倒温度则无纬度分布格局。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胁迫温度的敏感性也更高，这支持了急性与慢性耐热性之间存在权衡关系。相反，发育可塑性（developmental plasticity）并未影响临界热最大值，但提升了生物对慢性热暴露的耐受性。通过热致死时间曲线得到的研究结果，有助于理解为何耐热性与纬度之间的关联取决于所采用的研究方法，因此这类曲线能够为耐热性提供更完整且可靠的量化手段。