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The blind cave salamander: a small creature with a large ability, by Maggie May

June 22, 2011

Imagine being in a dark room, not being able to see a thing, and the only way to get out is by the direction of a magnetic pull deep in the Earth’s surface. It is very common that when an organism of any kind loses a sense, such as sight or sound, the other senses become heightened in order to compensate and allow the organism to survive. How do organisms that reside in confined, dark spaces navigate through their environment? The answer may come from the Earth’s magnetic field.

There is a small, unique creature that senses these magnetic pulls deep in the Earth in order to move around its environment. The blind cave salamander, also known as the olm, is an amphibian that has evolved to have undeveloped eyes, leaving it blind. This animal dwells in the subterranean waters of caves in Europe, and because of the dark environment, it has little use for sight. In some individuals, there are no eyes present, while in others the eyes are undeveloped and covered with skin. Unlike most amphibians, the blind cave salamander is entirely aquatic in that its entire life is spent underwater breathing through external gills. In order to survive, its underwater senses are of utmost importance in allowing it to catch prey and escape from predators. When sight, smell, and sound cannot be utilized, the special ability of sensing the magnetic pulls deeps in the Earth comes into play for the blind cave salamander.

Peter Schlegel, Sebastian Steinfartz, and Boris Bulog have conducted a study providing strong evidence that the blind cave salamander, and other cave dwelling salamanders, utilize magnetic fields to help them orient in their dark underwater environments. The main sense of navigation and movement for these species has been heightened underwater hearing. These researchers wanted to determine how sensing the Earth’s magnetic field improved the animal’s orientation and navigation in the dark. The ability to sense magnetic fields can be disturbed by light and sound, so the researchers set up two separate experiments. One was to have disturbances allowed to understand how they would navigate in their normal habitats with all senses available for use. The other was to remove all disturbances to determine how the salamanders would navigate using only magnetic reference. The Earth’s magnetic field is permanent, meaning that it can always serve as a reliable source of navigation for the blind cave salamander.  These researchers wanted to determine if the salamanders could move using only their magnetic senses.

The salamanders studied were obtained from breeding stocks raised in an experimental cave, called Moulis cave, and the natural waters of other caves in Slovenia. Since all forms of light were to be avoided, the experiments were conducted under dim infrared light in one of the laboratories in Moulis cave. Sessions were run under natural and artificial magnetic conditions. The animals were placed in large glass bowls with cave water approximately thirty centimeters in diameter.  The bowls were set in the center of Helmholtz coils, a system in which a magnetic field around the bowl can be created and controlled.  The blind cave salamanders’ movements and body alignment reactions were counted and recorded according to the direction of the magnetic field. This allowed the researchers to analyze exactly how the animal senses and responds to magnetic factors.

The main outcome of the study suggested that the blind cave salamander navigated according to a magnetic field, but interestingly preferred a single magnetic direction. This means that the salamander was able to move around the bowl by sensing the pull of the magnets, but made more vigorous movements when the magnetic pull was in a specific direction. Every time this direction was tested for a single salamander, they had the same aggressive movements. When multiple directions were tested at one time, the salamander would still align its body towards its favorite direction. It was intriguing that this direction was the same as the magnetic pull in their habitat, meaning the same direction as the caves they were pulled from.

In a natural setting, other physical parameters are present that can help in navigation, such as light, sound, and temperature. Schlegel, Steinfartz, and Bulog tested the salamanders’ body alignments and movements with magnetic factors along with the presence of other sensory sources mentioned above. When the other physical parameters were present, the salamanders aligned according to all factors, meaning that they did not only point to the magnetic direction, but alternated between the magnetic pull and physical sources. For instance, if a sound was heard they either moved away from it or towards it. This proved that they react to both magnetic and non-magnetic competitors, and that in a natural setting will utilize all senses for navigation and survival purposes.

Schlegel and his coworkers then tested navigation and alignment based only on the magnetic field in a natural setting, different from the artificial testing they previously performed. They found that the salamanders aligned differently than when there were other sensory sources available. Again, they observed that the animals preferred the magnetic direction that was congruent with their natural habitat.  This proved to be a key factor to Schlegel, Steinfartz, and Bulog’s experiment, since the Earth’s magnetic field is the only permanent sensory source available for the blind cave salamander’s use.

Schlegel’s line of study has proven the fact that the blind cave salamander has geomagnetic senses, allowing it to navigate based on the direction of the Earth’s magnetic field. While this is a recent discovery, it is one that is sure to be tested on other organisms that have sensory deprivations. How many animals out there have this unique ability? Is this something that could be utilized by technology? If so, it could be a solution for humans who are blind.

The adaptations of the blind cave salamander have made it to be a truly remarkable animal. The evolutionary changes of its heightened senses portray the measures an organism can go to in order to survive. There is no single sense used for navigation or survival purposes in any organism, and Schlegel, Steinfartz, and Bulog proved that in their study. It is evident that multiple senses are needed and utilized for navigation purposes. Underlying environmental factors have proven to be critical for the survival of the blind cave salamander, as well as other cave-dwelling salamanders.

References

Bulog, B. & Van der Meijden, A. (1999). Proteus anguinus. www.amphibiaweb.org.

Bulog, B. & Schlegel, P. (2000). Functional morphology of the inner ear and underwater audiograms of Proteus anguinus (Amphibia, Urodela). Eur. J. Physiol., 439, R165-R167.

Fischer, J.H., Freake, M.J., Borland, S.C. & Phillips J.B. (2001). Evidence for use of magnetic map information by an amphibian. Anim. Behav., 62, 1-10.

Phillips, J.B. (1997). Use of earth’s magnetic field by orienting cave salamanders. J. Comp.  Physiol., 121, 273-288.

Schlegel, P.A., Steinfartz, S. & Bulog. (2009). Non-visual sensory physiology and magnetic orientation in the Blind Cave Salamander, Proteus angiunus (and some other cave-dwelling urodele species). Review and new results on light-sensitivity and non-visual orientation in subterranean urodeles (Amphibians). An. Biol. 59, 351-384.

 

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