Heritable variation in the timing of rhythmic events with respect to daily time cues gives rise to chronotypes. Despite its importance, the mechanisms (clock or non-clock) regulating chronotypes remain elusive. Using artificial laboratory selection for divergent phasing of emergence of adults from pupae, our group has derived populations of Drosophila melanogaster which are early and late chronotypes for eclosion rhythm. Several circadian rhythm characteristics of these populations have since been described. We hypothesized that our selection protocol has inadvertently resulted in selection for masking, a non-clock phenomenon, in the early chronotype due to the placement of our selection window (which includes the lights-ON transition). We designed experiments to discriminate between enhanced masking to light versus circadian clock mediated changes in determining enhanced emergence in the morning window in our early chronotypes. Using a series of phase-shift protocols, LD-DD transition, and T-cycle experiments, we find that our early chronotypes have evolved positive masking, and their apparent entrained phases are largely contributed by masking. Through skeleton T-cycle experiments, we find that in addition to the evolution of greater masking, our early chronotypes have also evolved advanced phase of entrainment. Furthermore, our study systematically outlines experimental approaches to examine relative contributions of clock versus non-clock control of an entrained behavior. Although it has previously been suggested that masking may confer an adaptive advantage to organisms, here we provide experimental evidence for the evolution of masking as a means of phasing that can complement clock control of an entrained behavior.

与日常时间线索相关的节律事件时间的可遗传变异导致了时间型。尽管它很重要，但调节时间型的机制（时钟或非时钟）仍然难以捉摸。使用人工实验室选择对成虫从蛹出现的不同阶段进行，我们的小组已经衍生出黑腹果蝇种群，它们是羽化节律的早期和晚期计时型。这些人群的几个昼夜节律特征已经被描述。我们假设我们的选择协议在早期无意中导致了屏蔽选择，这是一种非时钟现象由于我们的选择窗口的位置（包括开灯转换）而导致的时间类型。我们设计了实验来区分增强的光掩蔽与生物钟介导的变化，以确定在我们早期的时间型中的早晨窗口中的增强出现。使用一系列相移协议、LD-DD 转换和T循环实验，我们发现我们的早期时间型已经进化出正掩蔽，它们明显的夹带阶段在很大程度上是由掩蔽造成的。通过骨架T循环实验，我们发现除了更大掩蔽的进化之外，我们早期的计时型也进化到夹带的高级阶段。此外，我们的研究系统地概述了实验方法，以检查时钟与非时钟控制对夹带行为的相对贡献。尽管先前有人建议掩蔽可能赋予生物体适应性优势，但在这里我们为掩蔽的进化提供了实验证据，作为一种可以补充对夹带行为的时钟控制的定相手段。