Data from: Flying Drosophila maintain arbitrary but stable headings relative to the angle of polarized light

Animals must use external cues to maintain a straight course over long distances. In this study, we investigated how the fruit fly, Drosophila melanogaster, selects and maintains a flight heading relative to the axis of linearly polarized light, a visual cue produced by the atmospheric scattering of sunlight. To track flies' headings over extended periods, we used a flight simulator that coupled the angular velocity of dorsally presented polarized light to the stroke amplitude difference of the animal's wings. In the simulator, most flies actively maintained a stable heading relative to the axis of polarized light for the duration of 15 minute flights. We found that individuals selected arbitrary, unpredictable headings relative to the polarization axis, which demonstrates that Drosophila can perform proportional navigation using a polarized light pattern. When flies flew in two consecutive bouts separated by a 5 minute gap, the two flight headings were correlated, suggesting individuals retain a memory of their chosen heading. We found that adding a polarized light pattern to a light intensity gradient enhanced flies' orientation ability, suggesting Drosophila use a combination of cues to navigate. For both polarized light and intensity cues, flies' capacity to maintain a stable heading gradually increased over several minutes from the onset of flight. Our findings are consistent with a model in which each individual initially orients haphazardly but then settles on a heading which is maintained via a self-reinforcing process. This may be a general dispersal strategy for animals with no target destination.动物需依托外部线索实现长距离直线行进。本研究以黑腹果蝇（Drosophila melanogaster）为对象，探究其如何依据太阳光经大气散射产生的线偏振光（linearly polarized light）轴，选择并维持飞行航向。为实现果蝇飞行航向的长时间追踪，我们搭建了一套飞行模拟器（flight simulator）：该装置将背部投射的偏振光的角速度，与果蝇的翅膀冲程幅度差进行耦合联动。在该模拟器中，多数果蝇可在15分钟的飞行过程中，主动维持与偏振光轴相对稳定的飞行航向。我们发现，单只果蝇会选择相对于偏振光轴而言任意且不可预测的飞行航向，这一结果证实果蝇可依托偏振光模式完成比例导航（proportional navigation）。当果蝇完成两次间隔5分钟的连续飞行回合后，两次的飞行航向存在显著相关性，这表明果蝇能够保留对自身所选航向的记忆。我们还发现，在光强梯度中加入偏振光模式，可提升果蝇的定向能力，这说明果蝇会结合多种线索完成导航。无论是依托偏振光还是光强线索，果蝇维持稳定航向的能力均会在飞行启动后的数分钟内逐步提升。我们的研究结果与下述理论模型相符：个体果蝇初始时会随机定向，随后选定某一固定航向，并通过自我强化的过程维持该航向。对于无明确目标目的地的动物而言，这或许是一种通用的扩散策略。