Declining calcium in freshwater lakes has become a serious threat to aquatic organisms, which may affect the anti-fish defense of cladocerans with high calcium demand. To evaluate the effects of low calcium on life history strategies of cladocerans for defending against fish predation, we exposed Ceriodaphnia cornuta to eight concentrations of calcium ranging from 0.5 to 50.0 mg L⁻¹ in the absence and presence of fish kairomone, and observed the changes in body surface, recorded the key life-history traits, and calculated the degree of its induced defense response. Results showed that, on average, low calcium (0.5, 1.0, 1.5 mg L⁻¹) significantly reduced survival, maternal body size at maturation, and total offspring per female by 66.7%, 8.0%, and 48.8%, respectively, compared with those exposed to normal calcium level (10.0 mg L⁻¹). At the normal calcium level, fish kairomone shortened the time to maturation, reduced maternal body size at maturation, and increased total offspring by 15.7%, 11.0%, and 29.6%, respectively, compared with those not exposed to fish kairomone. In the presence of fish kairomone, the reproduction of C. cornuta was affected by a narrower range of calcium concentrations. Calcium concentrations and fish kairomone showed a significant interaction on maternal body size at maturation, total offspring, and body size of neonates, i.e., low calcium impaired the life history defenses involved in maternal development, but enhanced the defense traits involved in reproductive performance, which indicated the diversified interference effects of decreased calcium on the life history defense strategies of C. cornuta against fish predators.

中文翻译：

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降低的钙浓度会干扰 Ceriodaphnia cornuta 响应鱼 kairomone 的生活史防御策略

淡水湖泊中钙的减少已成为对水生生物的严重威胁，这可能会影响对钙需求量高的枝角类动物的抗鱼防御。为了评估低钙对枝角类动物防御鱼类捕食的生活史策略的影响，我们在不存在和存在鱼类 kairomone 的情况下将Ceriodaphnia cornuta暴露于 0.5 至 50.0 mg L ^{-1 的}八种钙浓度，并观察了变化在体表中，记录关键的生活史特征，并计算其诱导防御反应的程度。结果显示，平均而言，低钙（0.5、1.0、1.5 mg L ^-1) 与暴露于正常钙水平 (10.0 mg L ^-1 ) 的那些相比，显着降低了存活率、成熟时的母体体型和每个雌性的总后代数量分别为 66.7%、8.0% 和 48.8% 。在正常钙水平下，与未暴露于鱼类 kairomone 的那些相比，鱼 kairomone 缩短了成熟时间，减少了成熟时母体的体型，并使总后代分别增加了 15.7%、11.0% 和 29.6%。在鱼利它素的存在下，的再现C.枸骨受更窄范围的钙浓度影响。钙浓度和鱼类凯罗酮对成熟时母体的体型、后代的总体型和新生儿的体型有显着的相互作用，即低钙损害了母体发育中涉及的生活史防御，但增强了生殖性能中涉及的防御特征，表明减少钙对C.cornuta对鱼类捕食者的生活史防御策略的多样化干扰作用。