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.

动物需借助外部线索，才能在长距离移动中保持直线行进路径。本研究聚焦黑腹果蝇（Drosophila melanogaster）如何基于线偏振光（linearly polarized light）的光轴选择并维持飞行航向——这类由太阳光经大气散射形成的视觉线索。为长期追踪果蝇的飞行航向，我们搭建了一套飞行模拟器（flight simulator）：该装置将背向呈现的偏振光的角速度，与果蝇的翼拍幅差进行耦合联动。在该模拟器中，多数果蝇可在15分钟的飞行时长内，主动维持与偏振光轴相对稳定的飞行航向。我们发现，果蝇个体可自主选择与偏振光轴无固定关联的、不可预测的航向，这证明黑腹果蝇能够基于偏振光模式完成比例导航（proportional navigation）。当果蝇在两次间隔5分钟的连续飞行回合中飞行时，两次飞行的航向存在相关性，这表明果蝇能够保留对所选航向的记忆。我们还发现，在光强梯度中叠加偏振光模式，可提升果蝇的定向能力，这表明黑腹果蝇会结合多种线索进行导航。无论是偏振光线索还是光强线索，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模型相符：果蝇个体最初会随机定向，随后选定某一航向，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。