The Earth’s magnetic field calibrates their navigation system

They are only a few centimeters long and their brains have a relatively simple structure with fewer than a million neurons. However, desert ants of the genus Cataglyphis possess abilities that set them apart from many other creatures: the animals are able to orient themselves relative to the Earth’s magnetic field.

A research team from the Julius-Maximilians-University of Würzburg (JMU) discovered this a few years ago. However, it was not yet known where in the ant brains magnetic information is processed. This is now resolved.

In a new study published in the journal Proceedings of the National Academy of Sciencesthe team shows that information about the Earth’s magnetic field is mainly processed in the ants’ internal compass, the so-called core complex, and in the bodies of mushrooms, the animals’ learning and memory centers.

Professor Wolfgang Rössler, Chair of Behavioral Physiology and Sociobiology at the University of Würzburg, Dr Pauline Fleischmann, former scientist at the Chair of Behavioral Physiology and Sociobiology and now member of the Neurosensorics/Animal Navigation working group of the University of Oldenburg and Dr Robin Grob, who has since left the Rössler Professorship to join the Norwegian University of Science and Technology in Trondheim, were responsible for this study.

First exploratory steps for calibration

“Before an ant leaves its underground nest for the first time and goes in search of food, it must calibrate its navigation system,” says Fleischmann to explain the context of his work. During so-called learning walks, the animals then explore the immediate surroundings around the nest entrance and pirouette repeatedly around their own body axis with short stops in between. During these breaks, they always look exactly in the direction of the nest entrance, even if they cannot see the small hole in the ground.

Through their field studies in southern Greece, where Cataglyphis ants originate, Fleischmann and his colleagues were able to prove that desert ants orient themselves according to the Earth’s magnetic field during the learning phase of walking. Fleischmann and Grob studied the orientation behavior of ants during magnetic field manipulation, but also looked for changes in the nervous system of Cataglyphis as an expression of newly acquired experience.

A faulty magnetic field disrupts the learning process

The zoologists focused on young workers who had not yet undertaken learning walks. Ants were only allowed to leave in carefully planned experiments, sometimes in natural conditions, sometimes in a continuously manipulated magnetic field that, for example, displayed chaotic directions or did not allow horizontal orientation. This erroneous directional information did not provide a reliable reference system for the ants’ behavior when looking toward the nest entrance during learning walks.

“Our neuroanatomical analyzes of the brain show that ants exposed to an altered magnetic field have a smaller volume and fewer synaptic complexes in an area of ​​the brain responsible for integrating visual information and learning, the so-called the body of the mushroom,” explain Fleischmann and Grob. . In the central complex, the region of the ant brain in which spatial orientation is anchored, the same results were observed under certain conditions.

The number of synaptic connections increases

Desert ants allowed to make their first excursions in natural conditions were clearly different. Their sensory experiences, a combination of information about the magnetic field, the position of the sun and the visual environment, triggered a learning process that was accompanied by structural changes in neurons and an increase in synaptic connections in the aforementioned brain regions.

According to scientists, this leads to the conclusion that magnetic information serves not only as a compass for navigation, but also as a crucial overall reference system for the formation of spatial memory.

In search of the sensory organ

The results of their experiments prove “that ants need a functional magnetic compass during their learning walks in order to calibrate their visual compass and at the same time store images of the nest environment in their long-term memory “, explain Fleischmann and Grob. At the same time, their research extends well beyond the realm of compass calibration in ants.

Rössler emphasizes that “the results provide valuable insights into how multisensory stimuli can influence the neural plasticity of brain circuits for navigation in a critical phase of brain maturation.”

As a next step, the team wants to study in which sensory organ the desert ant receives magnetic information and through which sensory pathways it is transmitted and processed. This has not yet been achieved with any animal species that orients itself towards the Earth’s magnetic field.

Due to their manageable and relatively small nervous systems, insects, to which Cataglyphis belongs, offer a unique opportunity to study the neural bases of magnetic orientation at all levels.