A group of scientists, led by Dr Jon Pierce-Shimomura of the University of Texas at Austin, has identified a magnetosensitive neuron in the brain of Caenorhabditis elegans, a non-parasitic nematode that lives in the interstitial water of soils, feeding on bacteria.
Inside the head of the nematode Caenorhabditis elegans, an antenna-like structure at the tip of the AFD neuron (green) is the sensor for Earth’s magnetic field. Image credit: Andrés Vidal-Gadea.
Many organisms such as butterflies, birds, wolves and sea turtles, use the magnetic field of the Earth to navigate across the globe.
For a few species, central neurons responsive to Earth-strength magnetic fields have been discovered; however, magnetosensory neurons have never been identified in any animal – until now.
In a new study, Dr Pierce-Shimomura and co-authors discovered that hungry C. elegans in gelatin-filled tubes tend to move down, a strategy they might use when searching for food. When the scientists brought worms into the lab from other parts of the world, the worms didn’t all move down.
Depending on where they were from – Hawaii, England or Australia, for example – they moved at a precise angle to the magnetic field that would have corresponded to down if they had been back home.
For instance, Australian C. elegans moved upward in tubes. The magnetic field’s orientation varies from spot to spot on the planet, and each worm’s magnetic field sensor system is finely tuned to its local environment, allowing it to tell up from down.
“Populations isolated from around the world, migrated at angles to the magnetic vector that would optimize vertical translation in their native soil, with northern- and southern-hemisphere worms displaying opposite migratory preferences,” Dr Pierce-Shimomura and his colleagues wrote in a paper published in the journal eLife.
“C. elegans is just one of myriad species living in the soil, many of which are known to migrate vertically. I’m fascinated by the prospect that magnetic detection could be widespread across soil dwelling organisms,” said study’s lead author Dr Andrés Vidal-Gadea of Illinois State University.
The magnetosensitive neuron, called an AFD neuron, was already known to sense carbon dioxide levels and temperature.
Dr Pierce-Shimomura’s team discovered the magnetosensory abilities of C. elegans by altering the magnetic field around them with a special magnetic coil system and then observing changes in behavior.
The biologists also showed that C. elegans which were genetically engineered to have a broken AFD neuron did not orient themselves up and down as do normal worms.
Finally, they used a technique called calcium imaging to demonstrate that changes in the magnetic field cause the AFD neuron to activate.
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Andrés Vidal-Gadea et al. 2015. Magnetosensitive neurons mediate geomagnetic orientation in Caenorhabditis elegans. eLife, published online June 17, 2015; doi: 10.7554/eLife.07493
