TY - JOUR A1 - Fleischmann, Pauline N. A1 - Grob, Robin A1 - Rössler, Wolfgang T1 - Magnetosensation during re-learning walks in desert ants (Cataglyphis nodus) JF - Journal of Comparative Physiology A N2 - At the beginning of their foraging careers, Cataglyphis desert ants calibrate their compass systems and learn the visual panorama surrounding the nest entrance. For that, they perform well-structured initial learning walks. During rotational body movements (pirouettes), naïve ants (novices) gaze back to the nest entrance to memorize their way back to the nest. To align their gaze directions, they rely on the geomagnetic field as a compass cue. In contrast, experienced ants (foragers) use celestial compass cues for path integration during food search. If the panorama at the nest entrance is changed, foragers perform re-learning walks prior to heading out on new foraging excursions. Here, we show that initial learning walks and re-learning walks are structurally different. During re-learning walks, foragers circle around the nest entrance before leaving the nest area to search for food. During pirouettes, they do not gaze back to the nest entrance. In addition, foragers do not use the magnetic field as a compass cue to align their gaze directions during re-learning walk pirouettes. Nevertheless, magnetic alterations during re-learning walks under manipulated panoramic conditions induce changes in nest-directed views indicating that foragers are still magnetosensitive in a cue conflict situation. KW - path integration KW - landmark panorama KW - learning and memory KW - magnetic compass KW - navigation Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-266556 SN - 1432-1351 VL - 208 IS - 1 ER - TY - THES A1 - Grob, Robin T1 - The Function of Learning Walks of \({Cataglyphis Ants}\): Behavioral and Neuronal Analyses T1 - Die Funktion der Lernläufe in \(Cataglyphis\) Ameisen: eine Studie des Verhaltens und der neuronalen Auswirkungen N2 - Humans and animals alike use the sun, the moon, and the stars to guide their ways. However, the position of celestial cues changes depending on daytime, season, and place on earth. To use these celestial cues for reliable navigation, the rotation of the sky has to be compensated. While humans invented complicated mechanisms like the Antikythera mechanism to keep track of celestial movements, animals can only rely on their brains. The desert ant Cataglyphis is a prime example of an animal using celestial cues for navigation. Using the sun and the related skylight polarization pattern as a compass, and a step integrator for distance measurements, it can determine a vector always pointing homewards. This mechanism is called path integration. Since the sun’s position and, therefore, also the polarization pattern changes throughout the day, Cataglyphis have to correct this movement. If they did not compensate for time, the ants’ compass would direct them in different directions in the morning and the evening. Thus, the ants have to learn the solar ephemeris before their far-reaching foraging trips. To do so, Cataglyphis ants perform a well-structured learning-walk behavior during the transition phase from indoor worker to outdoor forager. While walking in small loops around the nest entrance, the ants repeatedly stop their forward movements to perform turns. These can be small walked circles (voltes) or tight turns about the ants’ body axes (pirouettes). During pirouettes, the ants gaze back to their nest entrance during stopping phases. These look backs provide a behavioral read-out for the state of the path integrator. The ants “tell” the observer where they think their nest is, by looking back to it. Pirouettes are only performed by Cataglyphis ants inhabiting an environment with a prominent visual panorama. This indicates, that pirouettes are performed to learn the visual panorama. Voltes, on the other hand, might be used for calibrating the celestial compass of the ants. In my doctoral thesis, I employed a wide range of state-of-the-art techniques from different disciplines in biology to gain a deeper understanding of how navigational information is acquired, memorized, used, and calibrated during the transition phase from interior worker to outdoor forager. I could show, that celestial orientation cues that provide the main compass during foraging, do not guide the ants during the look-backbehavior of initial learning walks. Instead Cataglyphis nodus relies on the earth’s magnetic field as a compass during this early learning phase. While not guiding the ants during their first walks outside of the nest, excluding the ants from perceiving the natural polarization pattern of the skylight has significant consequences on learning-related plasticity in the ants’ brain. Only if the ants are able to perform their learning-walk behavior under a skylight polarization pattern that changes throughout the day, plastic neuronal changes in high-order integration centers are induced. Especially the mushroom bogy collar, a center for learning and memory, and the central complex, a center for orientation and motor control, showed an increase in volume after learning walks. This underlines the importance of learning walks for calibrating the celestial compass. The magnetic compass might provide the necessary stable reference system for the ants to calibrate their celestial compass and learn the position of landmark information. In the ant brain, visual information from the polarization-sensitive ocelli converge in tight apposition with neuronal afferents of the mechanosensitive Johnston’s organ in the ant’s antennae. This makes the ants’ antennae an interesting candidate for studying the sensory bases of compass calibration in Cataglyphis ants. The brain of the desert navigators is well adapted to successfully accomplish their navigational needs. Females (gynes and workers) have voluminous mushroom bodies, and the synaptic complexity to store large amount of view-based navigational information, which they acquire during initial learning walks. The male Cataglyphis brain is better suited for innate behaviors that support finding a mate. The results of my thesis show that the well adapted brain of C. nodus ants undergoes massive structural changes during leaning walks, dependent on a changing celestial polarization pattern. This underlies the essential role of learning walks in the calibration of orientation systems in desert ants. N2 - Die Gestirne helfen nicht nur Menschen uns zurecht zu finden, sondern auch Tiere können Sonne, Mond und Sterne für Navigation nutzen. Dabei gilt es aber zu beachten, dass die Himmelskörper ihre Position abhängig von der Tageszeit, den Jahreszeiten und dem Standort auf der Erde verändern. Um anhand von Himmelseigenschaften erfolgreich navigieren zu können, ist es deshalb unerlässlich diese Himmelsrotation zu kennen und für sie zu kompensieren. Menschen haben dafür bereits in der Antike komplizierte Maschinen wie den Antikythera Mechanismus entwickelt, Tiere dagegen brauchen nur ihr Gehirn. Wüstenameisen der Galtung Cataglyphis sind kleine Meisternavigatoren. Sie benutzen einen Himmelskompass, basierend auf der Sonne und dem mit ihr assoziierten Polarisationsmuster des Himmels, und einen Schrittintegrator, um einen Vektor zu bestimmen, der immer genau zu ihrem Ausgangspunkt zurück zeigt. Dieser Orientierungsmechanismus heißt Wegintegration. Da sich allerdings die Position der Sonne am Himmel und damit auch das Polarisationsmuster des Himmels über den Tag verändern, muss Cataglyphis für diese Veränderung kompensieren. Würde sie das nicht tun, würde ihr Kompass morgens in eine ganz andere Richtung als abends zeigen. Deshalb müssen Ameisen den Sonnenverlauf erlernen bevor sie zu ihren weitläufigen Futtersuchläufen aufbrechen. Cataglyphis führt dazu ein strukturiertes Lernlaufverhalten durch während des Übergangs von Innendiensttier zu Sammlerinnen. Dabei laufen die Ameisen in kleinen Schlaufen um ihren Nesteingang und stoppen ihre Vorwärtsbewegung mehrmalig, um Drehungen durchzuführen. Diese Drehungen sind entweder kleine gelaufene Kreise (Volten) oder Drehungen um die eigene Achse (Pirouetten). Nur Cataglyphis, die Gegenden mit einem reichhaltigen visuellen Panorama bewohnen, führen Pirouetten aus bei denen sie zurück zu ihrem Nesteingang schauen. Dies legt nahe, dass während Pirouetten das Panorama gelernt wird. Während Volten wird wohl der Himmelskompass kalibriert. Die Rückdrehungen während ihrer Lernläufe geben die einmalige Möglichkeit, die Ameise zu „fragen“ wo sie denkt, dass ihr Nest sei und damit ihren Wegintegrator auszulesen. In meiner Doktorarbeit kombinierte ich viele biologischen Methoden unterschiedlicher Disziplinen um zu untersuchen wie die Ameisen ihre Navigationssysteme während der ersten Läufe außerhalb des Nestes erlernen, speichern, kalibrieren und später nutzen. Ich konnte zeigen, dass Himmelsinformationen, die bei Sammlerinnen als wichtigster 4 Kompass dienen, nicht für die Orientierung der Rückblicke während Lernläufen dienen. Stattdessen nutzten naive Cataglyphis nodus das Erdmagnetfeld als Kompass. Obwohl Himmelsinformationen nicht als Kompass während der Lernläufe genutzt werden, spielen sie eine essentielle Rolle für neuroplastische Veränderungen im Gehirn der Ameisen. Nur wenn Ameisen ihre Lernläufe unter einem Polaristaionsmuster, das sich über den Tag hinweg verändert, ausführen, kommt es zu plastischen Veränderungen in neuronalen Integrationszentren. Besonders die Pilzkörper, Zentren für Lernen und Gedächtnis, und der Zentralkomplex, Zentrum für Orientierung und Bewegungssteuerung, nehmen im Volumen nach Lernläufen zu. Lernläufe spielen also eine wichtige Rolle für die Kalibrierung der Navigationsinformationen. Das Erdmagnetfeld könnte das für die Kalibierung notwendige erdgebundene, stabile Referenzsystem bieten, an dem die Himmelsbewegung gelernt wird. Im Ameisengehirn laufen visuelle Informationen von den polarisatiossensitiven Ocelli mit Afferenzen des mechanosensitiven Johnstonschen Organ aus der Antenne zusammen. Die Antenne könnte daher eine wichtiges Organ für die Kalibrierung der Orientierungssysteme sein. Das kleine Gehirn der Ameisen ist bestens an ihre Anforderungen als große Navigatoren angepasst. Weibliche C. nodus (Arbeiterinnen und Königinnen) besitzen große Pilzkörper mit einer Anzahl an Synapsen, die es ihnen erlaubt eine Vielzahl von Umgebungsbildern zu speichern, die sie während ihrer initialen Lernläufe lernen müssen. Das männliche Cataglyphis-Gehirn ist besser auf angeborene Orientierungsstrategien angepasst, die ihm helfen einen Geschlechtspartner zu finden. Die Ergebnisse meiner Doktorarbeit zeigen, dass das an die navigatorischen Herausforderungen angepasste Gehirn von C. nodus signifikante neuronale Veränderungen in Abhängigkeit eines sich veränderten Polaristaionsmusters während der Lernläufe erfährt. Dies zeigt die essentielle Rolle der Lernläufe in der Kalibrierung der Navigationssysteme von Wüstenameisen. KW - Cataglyphis KW - Kompass KW - Navigation KW - Nahrungserwerb KW - Neuroethologie KW - Neuroethology KW - Polyethism KW - Learning Walk KW - Geomagnetic Field KW - Learning & Memory Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-290173 ER - TY - JOUR A1 - Grob, Robin A1 - Tritscher, Clara A1 - Grübel, Kornelia A1 - Stigloher, Christian A1 - Groh, Claudia A1 - Fleischmann, Pauline N. A1 - Rössler, Wolfgang T1 - Johnston's organ and its central projections in Cataglyphis desert ants JF - Journal of Comparative Neurology N2 - The Johnston's organ (JO) in the insect antenna is a multisensory organ involved in several navigational tasks including wind‐compass orientation, flight control, graviception, and, possibly, magnetoreception. Here we investigate the three dimensional anatomy of the JO and its neuronal projections into the brain of the desert ant Cataglyphis, a marvelous long‐distance navigator. The JO of C. nodus workers consists of 40 scolopidia comprising three sensory neurons each. The numbers of scolopidia slightly vary between different sexes (female/male) and castes (worker/queen). Individual scolopidia attach to the intersegmental membrane between pedicel and flagellum of the antenna and line up in a ring‐like organization. Three JO nerves project along the two antennal nerve branches into the brain. Anterograde double staining of the antennal afferents revealed that JO receptor neurons project to several distinct neuropils in the central brain. The T5 tract projects into the antennal mechanosensory and motor center (AMMC), while the T6 tract bypasses the AMMC via the saddle and forms collaterals terminating in the posterior slope (PS) (T6I), the ventral complex (T6II), and the ventrolateral protocerebrum (T6III). Double labeling of JO and ocellar afferents revealed that input from the JO and visual information from the ocelli converge in tight apposition in the PS. The general JO anatomy and its central projection patterns resemble situations in honeybees and Drosophila. The multisensory nature of the JO together with its projections to multisensory neuropils in the ant brain likely serves synchronization and calibration of different sensory modalities during the ontogeny of navigation in Cataglyphis. KW - ant brain KW - chordotonal organ KW - graviception KW - magnetic compass KW - multisensory integration KW - navigation KW - wind compass Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225679 VL - 529 IS - 8 SP - 2138 EP - 2155 ER - TY - JOUR A1 - Grob, Robin A1 - Fleischmann, Pauline N. A1 - Grübel, Kornelia A1 - Wehner, Rüdiger A1 - Rössler, Wolfgang T1 - The role of celestial compass information in Cataglyphis ants during learning walks and for neuroplasticity in the central complex and mushroom bodies JF - Frontiers in Behavioral Neuroscience N2 - Central place foragers are faced with the challenge to learn the position of their nest entrance in its surroundings, in order to find their way back home every time they go out to search for food. To acquire navigational information at the beginning of their foraging career, Cataglyphis noda performs learning walks during the transition from interior worker to forager. These small loops around the nest entrance are repeatedly interrupted by strikingly accurate back turns during which the ants stop and precisely gaze back to the nest entrance—presumably to learn the landmark panorama of the nest surroundings. However, as at this point the complete navigational toolkit is not yet available, the ants are in need of a reference system for the compass component of the path integrator to align their nest entrance-directed gazes. In order to find this directional reference system, we systematically manipulated the skylight information received by ants during learning walks in their natural habitat, as it has been previously suggested that the celestial compass, as part of the path integrator, might provide such a reference system. High-speed video analyses of distinct learning walk elements revealed that even exclusion from the skylight polarization pattern, UV-light spectrum and the position of the sun did not alter the accuracy of the look back to the nest behavior. We therefore conclude that C. noda uses a different reference system to initially align their gaze directions. However, a comparison of neuroanatomical changes in the central complex and the mushroom bodies before and after learning walks revealed that exposure to UV light together with a naturally changing polarization pattern was essential to induce neuroplasticity in these high-order sensory integration centers of the ant brain. This suggests a crucial role of celestial information, in particular a changing polarization pattern, in initially calibrating the celestial compass system. KW - sky-compass pathway KW - visual orientation KW - look-back behavior KW - desert ants KW - vector navigation KW - memory KW - central complex KW - mushroom body Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-159235 VL - 11 IS - 226 ER - TY - JOUR A1 - Fleischmann, Pauline N. A1 - Grob, Robin A1 - Rössler, Wolfgang T1 - Kompass im Kopf : wie Wüstenameisen lernen heimzukehren JF - Biologie in unserer Zeit N2 - Erfolgreiche räumliche Orientierung ist für viele Tiere eine alltägliche Herausforderung. Cataglyphis‐Wüstenameisen sind bekannt für ihre Navigationsfähigkeiten, mit deren Hilfe sie nach langen Futtersuchläufen problemlos zum Nest zurückfinden. Wie aber nehmen naive Ameisen ihre Navigationssysteme in Betrieb? Nach mehrwöchigem Innendienst im dunklen Nest werden sie zu Sammlerinnen bei hellem Sonnenschein. Dieser Wechsel erfordert einen drastischen Wandel im Verhalten sowie neuronale Veränderungen im Gehirn. Erfahrene Ameisen orientieren sich vor allem visuell, sie nutzen einen Himmelskompass und Landmarkenpanoramen. Daher absolvieren naive Ameisen stereotype Lernläufe, um ihren Kompass zu kalibrieren und die Nestumgebung kennenzulernen. Während der Lernläufe blicken sie wiederholt zum Nesteingang zurück und prägen sich so ihren Heimweg ein. Zur Ausrichtung ihrer Blicke nutzen sie das Erdmagnetfeld als Kompassreferenz. Cataglyphis‐Ameisen besitzen hierfür einen Magnetkompass, der bislang unbekannt war. N2 - Successful spatial orientation is a daily challenge for many animals. Cataglyphis desert ants are famous for their navi­gational performances. They return to the nest after exten­sive foraging trips without any problems. How do ants take their navigational systems into operation? After conducting different tasks in the dark nest for several weeks, they be­come foragers under bright sun light. This transition re­quires both a drastic switch in behavior and neuronal changes in the brain. Experienced foragers mainly rely on visual cues. They use a celestial compass and landmark panoramas. For that reason, naïve ants perform stereotype learning walks to calibrate their compass systems and ac­quire information about the nest’s surroundings. During their learning walks, the ants frequently look back to the nest entrance to learn the homing direction. For aligning their gazes, they use the earth’s magnetic field as a com­pass reference. This magnetic compass in Cataglyphis ants was previously unknown. KW - Cataglyphis-Wüstenameisen KW - Magnetkompass KW - Insektennavigation KW - Himmelskompass Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-219260 SN - 1521-415X VL - 50 IS - 2 ER - TY - JOUR A1 - Grob, Robin A1 - Heinig, Niklas A1 - Grübel, Kornelia A1 - Rössler, Wolfgang A1 - Fleischmann, Pauline N. T1 - Sex-specific and caste-specific brain adaptations related to spatial orientation in Cataglyphis ants JF - Journal of Comparative Neurology N2 - Cataglyphis desert ants are charismatic central place foragers. After long-ranging foraging trips, individual workers navigate back to their nest relying mostly on visual cues. The reproductive caste faces other orientation challenges, i.e. mate finding and colony foundation. Here we compare brain structures involved in spatial orientation of Cataglyphis nodus males, gynes, and foragers by quantifying relative neuropil volumes associated with two visual pathways, and numbers and volumes of antennal lobe (AL) olfactory glomeruli. Furthermore, we determined absolute numbers of synaptic complexes in visual and olfactory regions of the mushroom bodies (MB) and a major relay station of the sky-compass pathway to the central complex (CX). Both female castes possess enlarged brain centers for sensory integration, learning, and memory, reflected in voluminous MBs containing about twice the numbers of synaptic complexes compared with males. Overall, male brains are smaller compared with both female castes, but the relative volumes of the optic lobes and CX are enlarged indicating the importance of visual guidance during innate behaviors. Male ALs contain greatly enlarged glomeruli, presumably involved in sex-pheromone detection. Adaptations at both the neuropil and synaptic levels clearly reflect differences in sex-specific and caste-specific demands for sensory processing and behavioral plasticity underlying spatial orientation. KW - antennal lobe KW - synaptic plasticity KW - polymorphism KW - optic lobes KW - mushroom bodies KW - learning and memory KW - central complex Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257299 VL - 529 IS - 18 ER - TY - JOUR A1 - Rössler, Wolfgang A1 - Grob, Robin A1 - Fleischmann, Pauline N. T1 - The role of learning-walk related multisensory experience in rewiring visual circuits in the desert ant brain JF - Journal of Comparative Physiology A N2 - Efficient spatial orientation in the natural environment is crucial for the survival of most animal species. Cataglyphis desert ants possess excellent navigational skills. After far-ranging foraging excursions, the ants return to their inconspicuous nest entrance using celestial and panoramic cues. This review focuses on the question about how naïve ants acquire the necessary spatial information and adjust their visual compass systems. Naïve ants perform structured learning walks during their transition from the dark nest interior to foraging under bright sunlight. During initial learning walks, the ants perform rotational movements with nest-directed views using the earth’s magnetic field as an earthbound compass reference. Experimental manipulations demonstrate that specific sky compass cues trigger structural neuronal plasticity in visual circuits to integration centers in the central complex and mushroom bodies. During learning walks, rotation of the sky-polarization pattern is required for an increase in volume and synaptic complexes in both integration centers. In contrast, passive light exposure triggers light-spectrum (especially UV light) dependent changes in synaptic complexes upstream of the central complex. We discuss a multisensory circuit model in the ant brain for pathways mediating structural neuroplasticity at different levels following passive light exposure and multisensory experience during the performance of learning walks. KW - central complex KW - mushroom body KW - multisensory navigation KW - visual memory KW - neuronal and synaptic plasticity Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-325096 VL - 209 IS - 4 ER -