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.

探究种群如何适应气温上升，一直是生态学领域的一大难题。相关研究常通过评估多个种群，以检验是否存在针对温度条件的本地适应现象。由于时间限制制约了我们观测进化响应的能力，以空间代时间替代法（space-for-time substitution）的应用十分普遍。本研究采用复活生态学（resurrection ecology）方法，探究了水蚤（Daphnia pulicaria）种群的耐热性随时间的变化情况。最古老基因型所经历的环境温度，显著低于最新基因型所经历的温度。我们提出假说：克隆株适配其所处时期的温度条件。本研究开展了两组热激实验，两组实验的热暴露时长存在差异。整体趋势显示，最新基因型的耐热性显著高于古老基因型；热休克蛋白（heat shock protein, 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，但未随时间周期发生显著变化。本研究结果表明，温度可能是该种群的选择压力之一，尽管观测到的响应可能是多重选择共同作用的结果。先前的研究发现，该种群的遗传结构以及其他与人为活动变化显著相关的性状均发生了显著改变。复活生态学方法将有助于我们理解人为活动引起的温度变化与其他胁迫因子的交互作用，及其对自然种群进化命运的影响。