Data from: Does variation in the intensity and duration of predation drive evolutionary changes in senescence?

1. The evolutionary theory of senescence predicts that increased rates of extrinsic mortality select for faster declines in fertility and survival with age. One predicted mechanism is that increased mortality favors alleles that enhance fitness early in life at the expense of survival or reproduction later in life (antagonistic pleiotropy). 2. We tested these predictions in natural populations of Daphnia ambigua from lakes that vary in the severity and duration of fish predation. Daphnia are found in lakes with: (1) anadromous alewife (Alosa pseudoharengus) that migrate between marine and freshwater, (2) permanent landlocked alewife, and (3) no alewife. Daphnia are rare year-round in ‘landlocked lakes’ and are seasonally eliminated from the water column in ‘anadromous lakes’ due to the very strong predatory impact of anadromous alewife on populations of zooplankton. Previous work has also shown that intense seasonal bouts of predation by anadromous alewife has selected for increased allocation towards growth and reproduction in Daphnia found in lakes with anadromous alewife. Such variation in the risk of mortality and the expression of life history traits early in life provides the raw materials to test the evolutionary theory of ageing. 3. We reared replicate populations of Daphnia from all three lake types and quantified lifetime rates of offspring production and intrinsic survival. We found no differences in age-related declines in fertility or survival. Daphnia from anadromous lakes produced significantly more offspring throughout their lifetime despite no differences in lifespan or in the number of reproductive bouts compared with Daphnia from lakes with landlocked and no alewife. 4. The lack of divergence in ageing contradicts the prediction that elevated mortality rates drive evolutionary shifts in ageing. We reconcile these results by considering the predictions of theoretical frameworks that incorporate feedbacks associated with increased mortality such as density- and condition-dependent processes. Our results, which are better explained by a consideration of these processes, thus call for a greater consideration of models that more explicitly consider the ecology of focal organisms.1. 衰老进化理论（evolutionary theory of senescence）预测，外源性死亡率（extrinsic mortality）升高会选择出随年龄增长而生育率与存活率下降更快的表型。其中一种被提出的作用机制是：死亡率升高会青睐那些在生命早期提升适合度（fitness），却以生命后期的存活或繁殖为代价的等位基因（alleles），即拮抗多效性（antagonistic pleiotropy）。 2. 我们从鱼类捕食强度与持续时长存在差异的湖泊中采集了模糊水蚤（Daphnia ambigua）的自然种群，以此检验上述预测。这些湖泊中的水蚤种群可分为三类：(1) 栖息有洄游型西鲱（anadromous alewife，*Alosa pseudoharengus*，即往返海洋与淡水间洄游的西鲱）；(2) 栖息有永久陆封型西鲱；(3) 无西鲱栖息。由于洄游型西鲱对浮游动物（zooplankton）种群具有极强的捕食压力，陆封型湖泊中的水蚤全年种群密度极低，而洄游型湖泊中的水蚤则会因季节性的捕食作用被逐出水体层。既往研究还表明，洄游型西鲱带来的高强度季节性捕食压力，已让栖息于此的水蚤演化出更多将资源分配给生长与繁殖的特征。这类死亡率风险与生命早期生活史性状（life history traits）表达的差异，为检验衰老进化理论提供了理想的实验材料。 3. 我们对三类湖泊来源的水蚤分别构建了重复种群，并量化了其终身繁殖速率与内在存活率。结果发现，各组水蚤的生育率与存活率随年龄的下降速率并无显著差异。尽管与陆封型及无西鲱湖泊中的水蚤相比，洄游型湖泊的水蚤在寿命与繁殖周期次数上并无不同，但其终身总产卵量显著更高。 4. 衰老速率未出现分化的结果，与“死亡率升高会驱动衰老的演化改变”这一经典预测相悖。我们通过纳入与死亡率升高相关的反馈过程（如密度依赖过程（density-dependent processes）与条件依赖过程（condition-dependent processes））的理论框架重新审视相关预测，以此调和本研究结果与既有理论的矛盾。相较于传统演化模型，纳入这类生态过程能更好地解释本研究发现，因此我们呼吁学界更多关注那些更明确纳入焦点生物（focal organisms）生态学特征的理论模型。