It has been a long-held belief in scientific circles that many creatures navigate across land, through water, and through the skies using the Earth’s magnetic field for guidance. Now scientists and engineers working at The University of Texas at Austin (UT) have finally discovered the organic mechanism responsible for this in an animal. Looking just like a microscopic TV antenna, the structure has been found in the brain of a tiny roundworm that uses it to work out which way to burrow through the soil. This breakthrough may help scientists discover how other species with internal compasses use the magnetic field of our planet to pilot their course.
Discovered in an round worm named Caenorhabditis elegans (C. elegans for short), the nanoscale sensor is located at the end of a neuron protruding from the worm’s brain. This gives rise to the hope that other animals may well share this attribute, particularly as parallels in brain structures exist across multiple species.
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"Chances are that the same molecules will be used by cuter animals like butterflies and birds," said Jon Pierce-Shimomura, assistant professor of neuroscience at UT and a member of the research team. "This gives us a first foothold in understanding magnetosensation in other animals."
The end of the neuron containing the magnetic field sensor in C. elegans is a branched projection called a dendrite. This particular dendrite is an AFD, so named because it has finger-like endings (hence the name, meaning Amphid Fingerlike Dendrite), and is already a particularly well-known structure in the world of worms as a sensor of carbon dioxide levels, ambient temperature, and – as discovered in recent work conducted by UT – humidity.
Building on this previous work with C. elegans on the ability of its AFD-paired neuron to react to changes in humidity, the researchers happened across the magnetosensory abilities of the worms when they tried altering the magnetic field around the worms to see what else this sensor could detect. What they discovered was that when exposed to alterations in the magnetic field, the worms were no longer be able to orient themselves up or down in their environment.
Using hungry C. elegans implanted in gelatin-filled tubes surrounded by an electromagnetic coil, the researchers noted that the worms ordinarily tended to move downward in their environment; an approach they would use when probing for food. When the coil was switched on and a stronger magnetic field than that of the Earth’s was introduced, the worms lost their way and began digging randomly, dependent upon the orientation of the induced magnetic field.
Intrigued by this behavior, the researchers hit on the idea of confirming their magnetic field theory by bringing in the same type of worm from various parts of the world and observing their orientation in a different environment. As a result the various C. elegans (from places as diverse as England, Hawaii, and Australia) all moved at exactly the angle in the tubes in relation to the local magnetic field that they would have perceived as "down" in their home environments. Australian worms, for example, burrowed their way up in the tubes.
The lead author of the study, Andrés Vidal-Gadea, former UT researcher and now a faculty member at Illinois State University, noted that C. elegans is just one of many thousands of species that exist in soil, a great number of which are recognized to move vertically in their environment.
"I'm fascinated by the prospect that magnetic detection could be widespread across soil dwelling organisms," said Vidal-Gadea.
If this magentosensory ability is widespread amongst soil-dwelling creatures, the team believes that one possible use for this discovery would be in the area of pest control in crops where, by simply altering the magnetic field in the land underneath the vegetation with electromagnetic coils, the creatures would be disoriented, dig down, get lost, and starve.
From a broader perspective, the discovery – if it is made in higher-order species – of a sensor capable of detecting the Earth's magnetic field would provide a vast range of scientific and technological research and application possibilities, with everything from ascertaining the mechanisms behind magnetically-guided migration of animals, through to the improvement of detection devices to aid in our own electronic navigation of the globe.
The results of this research were recently published in the journal eLife.