Data from: Resurrected “ancient” Daphnia genotypes show reduced thermal stress tolerance compared to modern descendants

Understanding how populations adapt to rising temperatures has been a challenge in ecology. Research often evaluates multiple populations to test whether local adaptation to temperature regimes is occurring. Space-for-time substitutions are common, as temporal constraints limit our ability to observe evolutionary responses. We employed a resurrection ecology approach to understand how thermal tolerance has changed in a Daphnia pulicaria population over time. Temperatures experienced by the oldest genotypes were considerably lower than the youngest. We hypothesized clones were adapted to the thermal regimes of their respective time periods. We performed two thermal shock experiments that varied in length of heat exposure. Overall trends revealed that younger genotypes exhibited higher thermal tolerance than older genotypes; heat shock protein (hsp70) expression increased with temperature and varied among genotypes, but not across time periods. Our results indicate temperature may have been a selective factor on this population, although the observed responses may be a function of multifarious selection. Prior work found striking changes in population genetic structure, and in other traits that were strongly correlated with anthropogenic changes. Resurrection ecology approaches should help our understanding of interactive effects of anthropogenic alterations to temperature and other stressors on the evolutionary fate of natural populations.

探究种群如何适应升温，一直是生态学领域的一大难题。现有研究常通过评估多个种群，以检验是否存在针对温度环境的本地适应现象。空间替代时间（space-for-time substitution）的研究策略十分常见，这是因为时间维度上的限制阻碍了我们直接观测进化响应的能力。为探究蚤状溞（*Daphnia pulicaria*）种群的热耐受性随时间的变化情况，我们采用了复活生态学（resurrection ecology）研究方法。最古老基因型所经历的环境温度显著低于较新的基因型。我们提出假设：各无性系均适应了其对应时期的温度环境。我们开展了两组热激实验，实验间的热暴露时长存在差异。整体趋势显示，较新的基因型相较于古老基因型，表现出更高的热耐受性；热休克蛋白70（heat shock protein 70，hsp70）的表达量随温度升高而上调，且在不同基因型间存在差异，但未随时间维度出现显著变化。本研究结果表明，温度或为作用于该种群的选择因子之一，尽管观测到的响应可能是多因子选择共同作用的结果。此前的研究发现，该种群的遗传结构以及其他与人类活动干扰显著相关的性状均发生了显著变化。复活生态学研究方法将有助于我们厘清温度及其他胁迫因子的人为改造所产生的交互效应，及其对自然种群进化命运的影响。