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

成功的导航对于所有移动的动物来说都是一项具有挑战性的任务。Cataglyphis蚂蚁是著名的路径整合导航实验模型。孤独的觅食者离开蚁穴入口--一个从蚂蚁的角度看不见的小孔--去寻找食物。找到猎物后，它们会以直线返回巢穴。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，并通过使用天生的里程计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性能外，这些蚂蚁在觅食生涯开始时还表现出另一种引人注目的行为-所谓的学习行走（LW）。LW是围绕着蚁穴入口的短暂探索之旅，在此期间，蚂蚁不收集任何食物，但获得成为觅食者所需的所有信息。在第一次广泛的觅食之旅，蚂蚁执行几个LW学习地标全景和校准他们的罗盘系统。LW包括脚尖旋转，即围绕蚂蚁的垂直轴的全部或部分旋转，这些旋转经常被停止阶段中断。在最长的停留时间里，蚂蚁会回头凝视巢穴入口，大概是为了记住归巢的方向。最近的研究表明，Cataglyphis蚂蚁使用地球的磁场作为指南针线索，在LW旋转时调整它们的凝视方向。因此，Cataglyphis蚂蚁使用至少两种不同的指南针系统，即天体指南针和磁指南针，通过PI导航。天体罗盘线索必须首先校准，因为它们显示季节和地理变化。相反，地球磁场提供了一个地球稳定的参考系统，原则上在暗巢中已经存在。关键的问题是-为什么Cataglyphis蚂蚁拥有两个不同的圆周率罗盘系统，这两个系统是如何联系起来的？- 是本项目的起点。 首先，我们想通过在现场进行行为操纵实验来更详细地研究新发现的磁罗盘。其次，我们将使用高速视频记录将原始LW与自然栖息地和实验室中觅食者的重新学习行走进行比较。最后，我们的目标是了解地磁和天体线索在LWs的行为和神经元水平上的作用。我们期待有价值的见解，新发现的磁罗盘Cataglyphis的功能，到两个罗盘线索都用于PI的动态使用，并到Cataglyphis的导航性能的神经基础。这些结果将是两个主要独立的研究领域的关键进展，即昆虫导航的神经行为学和磁感受的感觉生物学，并可能作为一个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.