The Dynamics of Geomagnetic and Celestial Compass Cues in Cataglyphis Ant Navigation

对所有可移动的动物来说，成功导航是一项具有挑战性的任务。巨形蚁是著名的路径积分导航实验模型。孤独的觅食者离开巢穴入口——一个蚂蚁看不见的小洞——去寻找食物。找到猎物后，它们会直线返回巢穴。觅食者依靠天体罗盘的线索（例如偏振模式或太阳的位置）来确定他们的行进方向，并使用先天的里程表来测量他们的行进距离。除了在觅食过程中令人印象深刻的导航表现外，这些蚂蚁在觅食生涯的开始还表现出另一种惊人的行为——所谓的学习行走（LWs）。LWs是围绕巢穴入口的短暂探索之旅，在此期间蚂蚁不收集任何食物，但获取成为觅食者所需的所有信息。在第一次广泛的觅食之旅之前，蚂蚁会进行几次LWs来学习地标全景并校准它们的指南针系统。LWs包括旋转，即围绕蚂蚁垂直轴的全部或部分旋转，这些旋转经常被停止阶段打断。在最长的停留时间里，蚂蚁凝视着巢穴入口，大概是为了记住回家的方向。最近，有研究表明，巨形蚁在LW旋转时使用地球磁场作为指南针线索来调整它们的凝视方向。因此，巨形蚁至少使用两种不同的罗盘系统，即天体罗盘和磁罗盘，通过圆周率进行导航。天文罗盘的线索最初必须校准，因为它们显示季节和地理变化。相比之下，地球磁场提供了一个地球稳定的参考系统，原则上已经可以在黑暗的巢穴中使用。关键问题是——为什么巨形蚁拥有两种不同的PI罗盘系统，这两种系统是如何联系在一起的？-是当前项目的起点。首先，我们希望通过实地的行为操纵实验，对新发现的磁铁罗盘进行更详细的研究。其次，我们将使用高速录像将naïve LWs与觅食者在自然栖息地和实验室中的重新学习行走进行比较。最后，我们旨在了解地磁和天体信号在LWs中在行为和神经元水平上的作用。我们期待对新发现的Cataglyphis磁铁罗盘的功能，对两种用于PI的罗盘线索的动态使用，以及Cataglyphis导航性能背后的神经元基础有有价值的见解。这些结果对于昆虫导航的神经行为学和磁感觉的感觉生物学这两个迄今为止主要独立的研究领域将是至关重要的进展，并可能作为一个新的研究方向的开始。

Successful navigation is a challenging task for all mobile animals. Cataglyphis ants are famous experimental models for navigation by means of path integration (PI). Solitary foragers leave the nest entrance – a tiny hole invisible from the ant’s perspective – to search for food. After finding prey, they return to the nest in a straight line. Foragers determine their directions travelled by relying on celestial compass cues (e.g. the polarization pattern or the sun’s position) and measure their distances travelled by using an innate odometer. Besides Cataglyphis’ impressive navigational performance during foraging, these ants show another striking behavior – so-called learning walks (LWs) – at the beginning of their foraging careers. LWs are short, explorative trips around the nest entrance during which ants do not collect any food, but acquire all information necessary to become foragers. Before the first extensive foraging trip, ants perform several LWs to learn the landmark panorama and to calibrate their compass systems. LWs include pirouettes, i.e. full or partial turns about the ant’s vertical axis that are frequently interrupted by stopping phases. During the longest stop ants gaze back to the nest entrance presumably to memorize the homing direction. Recently, it has been shown that Cataglyphis ants use the earth’s magnetic field as a compass cue to align their gaze directions during LW pirouettes. Therefore, Cataglyphis ants use at least two different compass systems, i.e. a celestial compass and a magnetic compass, to navigate by means of PI. Celestial compass cues have to be initially calibrated as they show seasonal and geographical variation. In contrast, the earth’s magnetic field offers a geostable reference system that is in principle already available in the dark nest. The key question – why do Cataglyphis ants possess two different compass systems for PI and how are these two systems linked? – is the starting point of the current project. First, we want to investigate the newly-discovered magnet compass in more detail by performing behavioral manipulation experiments in the field. Secondly, we will compare naïve LWs with re-learning walks of foragers in the natural habitat and the lab using high-speed video recordings. Finally, we aim to understand the role of geomagnetic and celestial cues during LWs on the behavioral and the neuronal level. We expect valuable insights into the functioning of the newly-discovered magnet compass of Cataglyphis, into the dynamic use of two compass cues both used for PI, and into the neuronal basis underlying Cataglyphis’ navigational performance. These results will be crucial progress for two as yet mostly separate research areas, i.e. neuroethology of insect navigation and sensory biology of magnetoception, and may act as the beginning of a new line of research.