Draft:Rüdiger Wehner

• Comment: This ended up just turning into a research summary of the subject's work, and is not a encyclopedic entry of a person. In turn, this just promotes the subject's work without actually focusing on the subject. Bobby Cohn (talk) 19:20, 29 November 2024 (UTC)

• Comment: Thanks for your submission! I'm not going to make a decision on this, but I want to note that large parts of this draft are excessively detailed summaries of the subject's research work which have too little relevance to a biography about the person themselves. I would recommend cutting that down a fair bit and focusing on the information directly related to their life. Let me know if you have any questions! (please  mention me on reply; thanks!) —TechnoSquirrel69 (sigh) 19:06, 29 November 2024 (UTC)

---

Rüdiger Wehner (born February 20, 1940) is a German neuroethologist known for his work surrounding the Cataglyphis fortis in 1968. His research surrounding the lifestyle of the novel thermophilic ants are composed and published in the literary textbook Desert Navigator: The Journey of an Ant, published in 2020.

Wehner's research focuses on the navigational abilities of the Cataglyphis fortis. Using innovative experimental designs, Wehner was able to define how ant's use their environment to determine their path back home. In modern times, Wehner was able to image the ant's brain to find the structures implicated in these unique behaviors.

Wehner has been a long-standing member with the University of Zürich, arriving in 1967, and eventually becoming the Director of the Institute of Zoology in 1976 staying in that position until 2005. Between his research expeditions, Wehner advocates for the expansion of junior research in myrmecology, encouraging "to find your own species, just as I did with the Cataglyphis."_­­­­

Early Life

Rüdiger Wehner was born in Nuremberg, Germany. On February 20, 1945, a week after his fifth birthday, a series of air raids pushed his family out of Dresden into the town of Radebeul. His new home was surrounded by a garden full of animals. Throughout his primary years, he identified birds through a book his mom had gifted him, sparking an interest in ornithology.

Education

From 1951-1960, Wehner attended Kaiserin-Friedrich-Gymnasium in Bad Homburg, Germany outside Frankfurt. Accompanied by a school friend in the surrounding woods of the school, they studied the behavior of songbirds, from breeding and feeding times to the behavior surrounding seasonal migration. This resulted in his first publication.

In 1960, after receiving his Abitur, Wehner enrolled in the University of Frankfurt where he shifted away from ornithology and studied biochemistry and neurophysiology, gaining more experience in the lab rather than the field.

In 1963, Martin Lindauer, a student of Karl von Frisch, became the director of the Institute of Zoology in Frankfurt. Wehner admired Lindauer's work, especially his experimental approach of analyzing the behavior of a freely moving organism.

In 1965, Wehner officially entered Lindauer's PhD program. His approach surrounded pattern discrimination in the visual system of honeybees. Over the course of two years, Wehner set up an efficient experimental design utilizing vertical stripes to see how honeybees process visual stimuli in order to spatially navigate the environment.

When Wehner finished his PhD in 1967, he was invited to work at the Zoological Institute at the University of Zürich to develop a neuroethology unit.¹ During this time, Wehner published many works concerning the spatial vision in honeybees and fruit flies.

Research

The "Failed" Experiment

While teaching at the University of Zürich in 1968, Wehner was looking for more ways to expand his research on honeybees. Lindauer sent him to Ramla, Israel where there was an orange orchard in full bloom, prime for foraging honeybees. Wehner set up all his equipment and waited. Despite using a highly concentrated sugar, he did not attract a single bee.

While waiting in an empty orchard, a Cataglyphis bicolor started to climb on his equipment. Stunned by their fast mobility and independent foraging, Wehner shifted his research towards the behavior of these unknown ants.

His pilot experiment was an improvisation using the tools he had brought with him for the honeybee tracking in Ramla. Him and his team went to the nests that the ants inhabited and marked off the areas with lines of thread in a grid formation to keep better track of the ant's navigational ability. Using a plastic tube, they displaced the foraging ants in random directions from their home and measured the amount of time it took them to reach their nest.

In 1969, Wehner composed a publication on the initial findings of the expedition. Based on the difference in displacement times, Wehner concluded that there were two visual mechanisms separating the navigational behavior between foraging and nesting ants.

Back in Zürich, Wehner began developing a research program on the Cataglyphis bicolor. Many of his colleagues expressed concerns, including Martin Lindauer. To start his study, he had to find a closer habitat of the Cataglyphis bicolor and after some relocation, him and his team settled in Mahres, Tunisia in 1969.

Cataglyphis Fortis Research

While in Mahres studying the Cataglyphis bicolor, a lonely Cataglyphis fortis came across Wehner's path. Rüdiger saw the ant slowly search around the sand and when they found a dead fly, they ran towards their nest in a straight line for over one hundred meters. Intrigued by the ant's complex behavior to navigate such a long distance with such precision, Wehner made his final shift in research focus from the Cataglyphis bicolor to the Cataglyphis fortis.

The Cataglyphis fortis inhabit the Sub-Saharan Salt Pan, a completely flat terrain, ideal for tracking behaviors. Instead of using thread, Wehner and his team marked a significant portion of the terrain in chalk lines resembling a grid like before. This allowed multiple behaviors of the Cataglyphis to be observed and analyzed. Due to the Sub-Saharan Salt Pan being completely flat, the only environmental conditions are the sunlight that causes extreme heat and wind from the various storms.

Over the course of fifty years, Wehner discovered the navigational toolbox that the Cataglyphis use to maneuver their harsh environment in complex and efficient ways. His experimental design paved the way for a simple yet more productive way of observing the behavior of the Cataglyphis. In 2020, Wehner's discoveries were composed into the literary textbook Desert Navigator: The Journey of an Ant.

Experimental Design

Karl Von Frisch previously demonstrated that insects could use visual compasses from the environment such as the sun to navigate. Still uncertain were the parts of the visual system that were affected in this type of navigation. Wehner and his team developed tools to manipulate the ant's visual perception without altering the natural terrain of the Sub-Saharan Salt Pan.

Through these innovative experimental designs, Wehner was able to find that the Cataglyphis has a visual compass based off polarization cues from the Sun.

The Orange Filter Trolley

Described as a "rolling optical laboratory", Wehner and his team constructed a trolley that the researcher pushed over an ant to allow complete manipulation of the skylight yet keeping the behavior undisturbed. By affecting the ant's cues of sunlight through the filter, the ant would pause and appear disoriented. This led to the first hypothesis that not just the position of the sun is important in navigation but rather the polarization of light from the sun.

Eye Caps  

To determine which parts of the eye were responsible for interpreting the polarization patterns, lacquer sheets were placed over the ant's eyes. Through behavioral tests and microscopic analysis of the retina, Wehner and his team concluded that the dorsal rim area, or the very top of the eye interprets UV light from the Sun. This was a breakthrough in Wehner's research as it broke the barrier from observing phenotypic behavior to locating parts of the visual system critical in navigational processes.

Odometers

Wehner wanted to see if the Cataglyphis had an internal odometer that would provide auxiliary information from their visual system. To test this, he and his team designed an experiment wherein an ant is placed in a 2-D metal channel that was some distance away from the nest. Once the ant reached the feeder, they were taken out and small stumps were glued to their legs. After, they got transferred to a new channel to be sent back to their nest. Wehner observed that the ants with stumps would overshoot or undershoot the target nest compared to those without stumps attached. Wehner concluded that the ants must have a stride integrator that gives them information on how many steps away home is.

The Visual Compass

After finding that the Cataglyphis need sunlight and vision for their navigational abilities, Wehner proceeded to determine the composition of the visual compass  and factors that influenced its function.

Polarization Compass

Polarized light is the angle in which the ant interprets a wavelength of light on a single plane. This light changes throughout the day as the Earth rotates in front of the Sun. By using channels that can be oriented to mimic specific orientations of sunlight, Wehner trained these ants by first placing them in these channels to localize their surroundings and after, sent them off to find their home. Wehner found there was a significant degree of systematic error in the ant's route back home when it was in a channel where the polarization of light was not parallel or at a right angle. He also found significant difference between the ant's homeward ability at different parts of the day when there were various light polarizations. These results show that the Cataglyphis orientation is misled when guided under different polarizations of light, proving that it is a critical factor in their navigational abilities. This finding was crucial in discovering the visual compass as it independently defined the polarization compass separate from the visual patterns of direct sunlight. As sailors used the sun's position to navigate the sea, the Cataglyphis use waves of light emitted from the sun to find their home.

Vector Navigation

Vector navigation is when an animal updates its path throughout the duration of the behavior. Wehner found that the ants abide by two coordinate systems that are constantly updating, the geocentric (information based on environment) and egocentric (information based on self). As an ant leaves its nest in search of food, the number of steps it takes to that food is tracked. When it finds food and begins to return to its nest, the ant determines whether it has arrived home based on a decreasing vector count of the number of steps it took. When the vector count reaches zero, the ant knows it has arrived home.

Path Integration

To demonstrate that the Cataglyphis constantly update their path to the nest, Wehner set up a barrier system to test their navigational awareness. The ants were sent in a straight line to a food source and once they reached it, the researchers set up barriers between the food and the home nest. Wehner found that when the ants reach a barrier, they exhibit a respite movement where they look around and acquire different environmental signals. Once it is done, it can go around the barrier and head to their nest in a straight line. This study established that the ant does not have to use memory-based recognition in determining its route back home but rather uses a constantly updating coordinate system based on their orientation.

Vector Recalibration

To study how the Cataglyphis manages to get back home when displaced, Wehner and his team set up Open Jaw tests. An ant is sent to the feeder and when they have captured their food, the researchers displace the ant to a separate location. At this location, the ant heads in a straight path to where they think their nest is, approaching vector zero. This leads the ant to a fictitious nest, or the nest they thought was real. Now, at vector zero, the ant recalibrates itself and searches for their real nest. The journey home from the fictitious nest employs the ant's search behavior. This causes them to loop around the place they called vector zero trying to find their real nest. Through this study, Wehner found the ants use a memory system to calibrate the steps they need to take (egocentric), but when displaced at vector zero, they resort to observing the environment for cues (geocentric) utilizing their path integrator. These separate systems of global and local vectors allowed Wehner to construct and develop the priorities within the navigational toolbox of the Cataglyphis.

Landmarks

By placing three plastic cylinders that act as landmarks around the nest of the Cataglyphis, Wehner observed that the ants use visual landmarks as cues to determine their nest entrance.

When the ants were trained to view landmarks and then displaced, they searched for their fictitious nest when they recognized the landmarks they have observed. Wehner described this behavior as the ant taking a snapshot of their environment that they can store and retrieve information from in order to find their home nest using landmarks in that snapshot.

Using a set of motor experiments, Wehner established that the ant could perceive visual landmarks that would build a panoramic view matching system. In this system the ant builds their recognition of landmarks on one big canvas that can be retrieved at any time for navigational guidance.

Learning Walks

Before a Cataglyphis becomes a foraging type, they must complete a series of learning walks to acclimate to the environment. This is where the ants wander around the nest, going farther each subsequent trial. Wehner observed that the Cataglyphis fortis increased its accuracy in finding their nest on each increasing learning walk even though they were farther away. Wehner found that these learning walks must provide the Cataglyphis with more than just one snapshot of their home, but rather a multitude of snapshots surrounding their home to always have different pictures for reference.

To test if the ant's needed various goal-related pictures to become experienced foragers, Wehner set up a moat system outside of the Cataglyphis' nests. This would inhibit the ant's ability to perform their learning walks while keeping the view of the environment intact. Inevitably, the ants would stumble into the water and return to the nest. To determine whether trained or untrained ants had better navigational abilities, Wehner and his team displaced the untrained and trained ants and observed the time it took for them to find their nest. Wehner saw that the untrained ants would get lost while the trained ants would find their nest, suggesting that the ants need some sort of memory matching technique for their homing ability.

Modern Cataglyphis Studies

With the advancement of neuroimaging in the twenty first century, Wehner leveraged these techniques to identify parts of the Cataglyphis brain that may contribute to its unique visual processing mechanisms. Given that the Cataglyphis brain is so small, Wehner focused on comparative volume studies of their during different behaviors and manipulations.

Central Complex

Since polarization cues are critical for foraging Cataglyphis, Wehner tested the volume of central complex, the area dedicated to processing orientation in insects, of the Cataglyphis under different exposures of light polarization. By using the innate mechanism of learning walks, Wehner exposed one group of ants to natural polarization and skylight and another group to a fixed amount of polarization and skylight. The volume of the central complex increased in the ants that had a variability in skylight versus those that had stagnant amounts. Without the ability to track neuronal activity, it can only be concluded that the volume increase of the central complex can only occur within an environment of natural polarization patterns.

Selected Publications

• Wehner, R. and Menzel, R. (1969). Homing in the ant Cataglyphis bicolor. Science 164, 192-194.
• Wehner, R., Herrling, P.L. and Flatt, I. (1970). Etude de l'orientation optique de Cataglyphis bicolor (Hymenoptera, Formicidae) dans son biotope désertique naturel. Ann. Inst. Nat. Rech. Agronom. Tunisie 43, 1-26.
• Wehner, R. and Duelli, P. (1971). The spatial orientation of desert ants, Cataglyphis bicolor, before sunrise and after sunset. Experientia 27, 1364- 1366.
• Wehner, R. (1972). Visual orientation performances of desert ants (Cataglyphis bicolor) toward astromenotactic directions and horizon landmarks. In Proc. AIBS Symp. Animal Orientation and Navigation (eds. S.R. Galler, K. Schmidt-Koenig,G.J. Jacobs and R.E. Belleville), pp. 421-436. Washington: U.S. Gov. Print.
• Wehner, R. and Flatt, I. (1972). The visual orientation of desert ants, Cataglyphis bicolor, by means of terrestrial cues. In Information Processing in the Visual Systems of Arthropods (ed. R. Wehner), pp. 295-302. Berlin, Heidelberg, New York: Springer.
• Wehner, R. and Räber, F. (1979). Visual spatial memory in desert ants, Cataglyphis bicolor (Hymenoptera, Formicidae). Experientia 35, 1569-1571.
• Wehner, R., Harkness, R.D. and Schmid-Hempel, P. (1983). Foraging Strategies in Individually Searching Ants - Cataglyphis bicolor (Hymenoptera: Formicidae). Mainz, Stuttgart: Fischer
• Wehner, R. and Wehner, S. (1986). Path integration in desert ants. Approaching a long-standing puzzle in insect navigation. Monitore zool. ital. (N.S.) 20, 309-331.