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

对于所有移动动物来说，成功的导航是一项具有挑战性的任务。Cataglyphis蚂蚁是著名的路径集成(PI)导航实验模型。孤独的觅食者离开蚁穴的入口处--在蚂蚁的视角下看不到的一个小洞--去寻找食物。在找到猎物后，它们会直线返回巢中。觅食者依靠天体罗盘信号(例如偏振模式或太阳的位置)来确定他们的行进方向，并使用固有的里程表来测量他们的行进距离。除了Cataglyphis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开始时还表现出另一种惊人的行为--所谓的学习行走(LWs)。LW是围绕蚁穴入口处的短暂探险之旅，在此期间，蚂蚁不收集任何食物，但获得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，蚂蚁会执行几次LW，以了解具有里程碑意义的全景图并校准它们的指南针系统。LW包括自旋，即围绕蚂蚁垂直轴的完全或部分旋转，经常被停止阶段打断。在停留时间最长的时候，蚂蚁会回头凝视巢穴的入口处，大概是为了记住回家的方向。最近，有研究表明，短尾蚂蚁利用地球磁场作为指南针信号，在LW旋转时调整它们的凝视方向。因此，Cataglyphis蚂蚁至少使用两种不同的罗盘系统，即天罗盘和磁罗盘，通过圆周率导航。由于天罗经显示出季节和地理上的变化，因此必须首先对它们进行校准。相比之下，地球磁场提供了一个地球稳定的参考系统，原则上在黑暗的巢穴中已经可以使用。关键问题--为什么Cataglyphis蚂蚁拥有两个不同的圆周率指南针系统，以及这两个系统是如何联系起来的？-是当前项目的起点。首先，我们想通过在野外进行行为操纵实验来更详细地研究新发现的磁罗盘。其次，我们将使用高速录像将幼稚的LW与在自然栖息地和实验室中重新学习的觅食者进行比较。最后，我们的目标是了解地磁和天体信号在LWS过程中在行为和神经元水平上的作用。我们期待着对新发现的Cataglyphis磁罗盘的功能、两个指南针线索的动态使用以及Cataglyphis导航性能背后的神经元基础的有价值的见解。这些结果对于昆虫导航的神经行为学和磁感应的感觉生物学这两个尚未基本分开的研究领域来说将是至关重要的进展，并可能成为一条新的研究路线的开始。

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.