Day–night cycle is the main zeitgeber (time giver) for biological circadian rhythms. Recently, it was suggested that natural diurnal geomagnetic variation may also be utilized by organisms for the synchronization of these rhythms. In this study, life‐history traits in Daphnia magna were evaluated after short‐term and multigenerational exposure to 16 h day/8 h night cycle, 32 h day/16 h night cycle, diurnal geomagnetic variation of 24 h, simulated magnetic variation of 48 h, and combinations of these conditions. With short‐term exposure, the lighting mode substantially influenced the brood to brood period and the lifespan in daphnids. The brood to brood period, brood size, and body length of crustaceans similarly depended on the lighting mode during the multigenerational exposure. At the same time, an interaction of lighting mode and magnetic variations affected to a lesser extent brood to brood period, brood size, and newborn's body length. The influence of simulated diurnal variation on life‐history traits in daphnids appeared distinctly as effects of synchronization between periods of lighting mode and magnetic variations during the multigenerational exposure. Newborn's body length significantly depended on the lighting regime when the periods of both studied zeitgebers were unsynchronized, or on the interaction of light regime with magnetic variations when the periods were synchronized. These results confirm the hypothesis that diurnal geomagnetic variation is an additional zeitgeber for biological circadian rhythms. Possible mechanisms for these observed effects are discussed. Bioelectromagnetics. © 2020 Bioelectromagnetics Society

中文翻译：

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磁变化和明暗循环的变化对水蚤生活史特征的影响。

昼夜周期是生物昼夜节律的主要时间（时间给予者）。最近，有人提出自然日变化的地磁变化也可以被生物利用来同步这些节律。在这项研究中，水蚤的生活史特征在短期和多代暴露于16 h日/ 8 h夜间周期，32 h日/ 16 h夜间周期，24 h的昼夜地磁变化，48 h的模拟磁变化以及这些条件的组合之后，对这些样本进行了评估。在短期暴露的情况下，光照模式极大地影响了雏鸟到雏鸟的时期和寿命。在多代接触中，甲壳动物的卵到卵的繁殖期，卵的大小和体长同样取决于光照模式。同时，光照模式和磁场变化的相互作用在较小程度上影响了育雏期，育雏期大小和新生儿的体长。模拟的昼夜变化对水蚤生活史特征的影响明显表现为多代暴露期间照明模式周期与磁变化之间的同步影响。当两个被研究的zeitgebers的周期不同步时，新生儿的体长显着取决于光照状态，或者当周期同步时，其光度与磁变化的相互作用取决于。这些结果证实了这样的假设，即地磁的昼夜变化是生物昼夜节律的另一个时代精神。讨论了这些观察到的影响的可能机制。生物电磁学。©2020生物电磁学会 当两个研究的时间周期不同步时，其体长显着取决于光照状态，或者当周期同步时，其光度与磁变化的相互作用。这些结果证实了这样的假设，即地磁的昼夜变化是生物昼夜节律的另一个时代精神。讨论了这些观察到的影响的可能机制。生物电磁学。©2020生物电磁学会 当两个研究的时间周期不同步时，其体长显着取决于光照状态，或者当周期同步时，其光度与磁变化的相互作用。这些结果证实了这样的假设，即地磁的昼夜变化是生物昼夜节律的另一个时代精神。讨论了这些观察到的影响的可能机制。生物电磁学。©2020生物电磁学会