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.解析种群如何适应气温上升，一直是生态学领域的一大难题。现有研究通常选取多个种群，以检验是否存在针对温度环境的本地适应现象。由于时间维度的观测限制了我们对进化响应的追踪能力，空间替代时间法（space-for-time substitution）在该类研究中应用广泛。本研究采用复活生态学（resurrection ecology）方法，探究了盔形溞（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年轻基因型，我们据此提出假说：各无性系均适应了其所处年代的温度环境。我们开展了两组热激实验（thermal shock experiment），实验的热暴露时长存在差异。整体趋势显示，年轻基因型的耐热性显著高于古老基因型；热休克蛋白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，但并未随年代发生显著变化。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受到多重选择的共同作用。前期研究已发现该种群的遗传结构以及其他与人类活动干扰密切相关的性状均发生了显著变化。复活生态学方法将有助于我们解析人类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。