A crucial property of circadian clocks is the ability to regulate the shape of an oscillation over its cycle length (waveform) appropriately, thus enhancing Darwinian fitness. Many studies over the past decade have revealed interesting ways in which the waveform of rodent behavior could be manipulated, one of which is that the activity bout bifurcates under environments that have 2 light/dark cycles within one 24-h day (LDLD). It has been observed that such unique, although unnatural, environments reveal acute changes in the circadian clock network. However, although adaptation of waveforms to different photoperiods is well studied, modulation of waveforms under LDLD has received relatively less attention in research on insect rhythms. Therefore, we undertook this study to ask the following questions: what is the extent of waveform plasticity that Drosophila melanogaster exhibits, and what are the neuronal underpinnings of such plasticity under LDLD? We found that the activity/rest rhythms of wild-type flies do not bifurcate under LDLD. Instead, they show similar but significantly different behavior from that under a long-day LD cycle. This behavior is accompanied by differences in the organization of the circadian neuronal network, which include changes in waveforms of a core clock component and an output molecule. In addition, to understand the functional significance of such variations in the waveform, we examined laboratory selected populations that exhibit divergent eclosion chronotypes (and therefore, waveforms). We found that populations selected for predominant eclosion in an evening window (late chronotypes) showed reduced amplitude plasticity and increased phase plasticity of activity/rest rhythms. This, we argue, is reflective of divergent evolution of circadian neuronal network organization in our laboratory selected flies.

中文翻译：

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黑腹果蝇的12 h T周期带动下的波形可塑性：行为，神经元网络和进化。

昼夜节律时钟的关键特性是能够在其周期长度（波形）上适当调节振荡形状的能力，从而增强达尔文的适应性。过去十年中的许多研究揭示了有趣的方式来控制啮齿动物行为的波形，其中之一是活动回合在一天24小时（LDLD）内有2个明/暗周期的环境中分叉。已经观察到，这种独特的，尽管不自然的环境揭示了昼夜节律网络的剧烈变化。然而，尽管已经很好地研究了波形对不同光周期的适应性，但是在LDLD下的波形调制在昆虫节律的研究中受到的关注相对较少。因此，我们进行了这项研究以提出以下问题：果蝇表现出波形可塑性的程度是什么，在LDLD下这种可塑性的神经元基础是什么？我们发现在LDLD下野生型果蝇的活动/休息节律不会分叉。相反，它们表现出与长期LD周期相似但明显不同的行为。这种行为伴随着昼夜节律神经网络的组织差异，其中包括核心时钟成分和输出分子的波形变化。另外，为了了解这种波形变化的功能重要性，我们检查了实验室选择的表现出不同的表型（因此是波形）的群体。我们发现，在傍晚的窗户（晚期表型）中以主要羽绒被选择的种群显示出活动/休息节律的幅度可塑性降低和相可塑性提高。我们认为，这反映了我们实验室选择的果蝇中昼夜节律神经网络组织的不同演变。