Where is the bat’s sixth sense?

A research team led by Dr. Oliver Lindecke and PD Dr. Christian Voigt from Leibniz-IZW has demonstrated for the first time that environmental cues important for navigation over long distances are acquired through the cornea of ​​a person eye.
Mammals see with their eyes, hear with their ears, and smell with their noses. But what sense or organ allows them to self-direct their migrations, sometimes far beyond their feeding grounds and thus requiring extensive navigational abilities?

The scientific experiments were led by Leibniz Institute of Animal and Wildlife (Leibniz-IZW) and chaired by Professor Richard A. Holland (Bangor University, UK) and Dr. Gunārs P ē tersons (Latvia University of Life Sciences and Technology). It shows that now the cornea of ​​the eye is the site of an important sense in bat migration. A bat’s directional sense is its eyes. If the cornea is anesthetized, the otherwise reliable sense of orientation will be disturbed while the ability to detect light remains unaffected. The paper was published in the scientific journal Communications Biology. In the bats of one experimental group, the scientists locally anesthetized the cornea with a drop of oxybuprocaine. This surfactant is widely used in ophthalmology, where it is used to temporarily desensitize the cornea when the human or animal eye is over-irritated. However, an effect on orientation has not been noted before. In another experimental group of bats, the team anesthetized the cornea of ​​one eye. Individuals in the control group were not given anesthesia, but were instead given isotonic saline as eye drops. All animals in this scientific experiment were captured in a migratory corridor on the Baltic coast and released individually in the open field 11 km from the place of capture. First, the scientists used bat detectors to ensure that no other bats were in the field at the time of releasing the test animals. The direction of movement of the released bats was observed without knowing how the bats were treated experimentally. Dr. Oliver Lindecke, first author of the paper, explains: “The control group and the anesthetized group with unilateral corneas clearly oriented to the expected south, while the bats with corneas were anesthetized. both sides fly in random directions.” He added: “This clear difference in behavior suggests that corneal anesthesia has disrupted the sense of direction, but orientation seems to still work well with one eye. The corneal treatment wore off after a short time, and the bats were able to continue their journey south after the trial.” To rule out the possibility that an irritated cornea also affects visual sensation and that the scientists could therefore draw erroneous conclusions, they performed an additional test. Again, they examined whether the bats’ response to light changed after anesthetizing the corneas on one or both sides. “We know from previous research that bats prefer a illuminated exit when leaving a simple Y-shaped maze,” explains PD Dr Christian Voigt, head of the Leibniz-IZW Department of Evolutionary Ecology . “In our experiment, animals that were anesthetized either unilaterally or bilaterally also showed this preference; we can therefore rule out that light vision has been altered after corneal treatment. The ability to see light will of course also affect long-distance navigation. ” For instance, many vertebrates such as bats, dolphins, whales, fish and turtles can safely navigate in the dark, whether it’s under the open night sky, when it’s cloudy at night or in caves and tunnels as well as in the depths of the ocean. For decades, scientists have searched for a sense or a sensory organ that enables animals to perform navigational and orientation tasks that seemed unimaginable to humans. Magnetic sensation, so far only demonstrated in certain mammalian species. Experiments show that iron oxide particles in cells can act as “microcompass needles”, as is the case with some species of bacteria. The team’s experiments on Lindecke and Voigt provide for the first time reliable data for determining sensory orientation in migratory, free-migrating mammals. Exactly what a bat’s cornea looks like, how it works, and whether it is a long-sought magnetic sense need to be pointed out in future scientific investigations.