The stability of circadian clock mechanisms under cyclic environments contributes to increased Darwinian fitness by accurately timing daily behavior and physiology. Earlier studies on biological clocks speculated that the timing of behavior and its accuracy are determined by the intrinsic period (τ) of the circadian clock under constant conditions, its stability, the period of the external cycle (T), and resetting of the clock by environmental time cues. However, most of these previous studies suffered from certain limitations, the major ones being a narrow range of examined τ values and a non-uniformity in the genetic background across the individuals tested. We present data that rigorously test the following hypotheses by employing Drosophila melanogaster fruit flies with τ ranging from 17 to 30 h in a uniform genetic background. We tested whether 1) precision (day-to-day stability of τ) is greater for clocks with τ close to 24 h; 2) accuracy (i.e., day-to-day stability of the phase relationship (ψ), where ψ is the duration between a phase of the rhythm and a phase of the external cycle) is greater for clocks with τ close to 24 h; 3) Ψ is delayed with an increase in τ; and 4) Ψ becomes more advanced with an increase in length of zeitgeber cycle (T). We show that precision is not always maximum for ~24-h clocks, but that accuracy is greatest when τ approximates T. Further, flies exhibit a delayed phase relationship with increasing τ and an advanced phase relationship under long T-cycles as compared with shorter T-cycles. We also describe relationships between activity and rest durations and how our observations fit predictions from models of circadian entrainment. Overall, we confirm that accuracy and phase of entrained rhythm are governed by both intrinsic clock period and the length of the external cycle; however, we find that the relationship between intrinsic period and precision does not fit previous predictions.

中文翻译：

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果蝇的昼夜节律特性及其相互关系作为自由运行时间的函数。

昼夜节律机制在循环环境下的稳定性通过精确计时日常行为和生理状况，有助于提高达尔文的适应性。早期对生物钟的研究推测，行为的定时及其准确性是由生物钟在恒定条件下的固有周期（τ），其稳定性，外部周期（T）以及通过环境时间提示。但是，大多数这些先前的研究都具有某些局限性，主要的是所检查的τ值范围狭窄，并且整个测试个体的遗传背景不均匀。我们提出的数据通过采用均匀分布的遗传背景中的τ在17至30 h范围内的果蝇果蝇来严格检验以下假设。我们测试了1）对于τ接近24 h的时钟，精度（τ的日常稳定性）是否更高；2）对于τ接近24 h的时钟，精度（即相位关系的日常稳定性（ψ），其中ψ是节奏的一个相位与外部循环的一个相位之间的持续时间）要大一些；3）Ψ随着τ的增加而延迟；4）随着Zeitgeber周期（T）长度的增加，Ψ变得更先进。我们显示，精度并非总是在约24小时的时钟中达到最高，但当τ接近T时，精度最高。此外，与较短的相比，苍蝇在τ增大时表现出延迟的相位关系，而在较长的T周期下表现出较高的相位关系。 T周期。我们还描述了活动时间与休息时间之间的关系，以及我们的观察结果如何符合昼夜节律携带模型的预测。总体，我们确认，节奏的准确性和相位受固有时钟周期和外部周期长度的控制；但是，我们发现固有周期与精度之间的关系不符合先前的预测。