Researchers discover first sensor of Earth's magnetic field in an animal

June 17, 2015
Researchers discover first sensor of Earth's magnetic field in an animal
Inside the head of the worm C. elegans, the TV antenna-like structure at the tip of the AFD neuron (green) is the first identified sensor for Earth's magnetic field. Credit: Andres Vidal-Gadea.

A team of scientists and engineers at The University of Texas at Austin has identified the first sensor of the Earth's magnetic field in an animal, finding in the brain of a tiny worm a big clue to a long-held mystery about how animals' internal compasses work.

Animals as diverse as migrating geese, sea turtles and wolves are known to navigate using the Earth's magnetic field. But until now, no one has pinpointed quite how they do it. The sensor, found in worms called C. elegans, is a microscopic structure at the end of a neuron that other animals probably share, given similarities in brain structure across species. The sensor looks like a nano-scale TV antenna, and the worms use it to navigate underground.

"Chances are that the same molecules will be used by cuter animals like butterflies and birds," said Jon Pierce-Shimomura, assistant professor of neuroscience in the College of Natural Sciences and member of the research team. "This gives us a first foothold in understanding magnetosensation in other animals."

The researchers discovered that hungry worms in gelatin-filled tubes tend to move down, a strategy they might use when searching for food.

When the researchers 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 worms moved upward in tubes. The magnetic field's orientation varies from spot to spot on Earth, and each worm's magnetic field sensor system is finely tuned to its local environment, allowing it to tell up from down.

The research is published today in the journal eLife.

The study's lead author is Andrés Vidal-Gadea, a former postdoctoral researcher in the College of Natural Sciences at UT Austin, now a faculty member at Illinois State University. He noted that 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 Vidal-Gadea.

The neuroscientists and engineers, who use C. elegans in their research into Alzheimer's disease and addiction, had previously discovered the worm's ability to sense humidity. That work led them to ask what else the worms might be able to sense, such as magnetic fields.

In 2012, scientists from Baylor College of Medicine announced the discovery of brain cells in pigeons that process information about magnetic fields, but they did not discover which part of the body senses the fields. That team and others have proposed a magnetosensor in the birds' inner ear.

"It's been a competitive race to find the first magnetosensory neuron," said Pierce-Shimomura. "And we think we've won with worms, which is a big surprise because no one suspected that worms could sense the Earth's magnetic field."

The neuron sporting a , called an AFD neuron, was already known to sense carbon dioxide levels and temperature.

The researchers discovered the worms' magnetosensory abilities by altering the magnetic field around them with a special magnetic coil system and then observing changes in behavior. They also showed that worms which were genetically engineered to have a broken AFD neuron did not orient themselves up and down as do normal . Finally, the researchers used a technique called calcium imaging to demonstrate that changes in the cause the AFD neuron to activate.

Explore further: A microscopic approach to the magnetic sensitivity of animals

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5 / 5 (2) Jun 17, 2015

What happens when the Earth's magnetic field shifts? Earth's magnetic field has flipped its polarity many times over the millennia...

Just curious.
5 / 5 (1) Jun 18, 2015
1 / 5 (2) Jun 18, 2015
The magnetic field sensors in animals are actually MHD sensors where conducting fluid produces electric current detected by neurons when moving through Earth's magnetic field.The intensity of the current relates to orientation of animal relative to the field direction enabling path tracking. Unfortunately it is not as reliable due to magnetic anomalies of paleomagnetism and variable magnetospheric compression.
5 / 5 (2) Jun 18, 2015

Why don't you provide some links to back up your "magnetic field sensors in animals are actually MHD sensors where conducting fluid produces electric current detected by neurons when moving through Earth's magnetic field."?

That's right, you can't because they don't exist.
5 / 5 (3) Jun 18, 2015
What happens when the Earth's magnetic field shifts?

The way I read the article is that there is a selective pressure for worms that have the 'correct' orientation (i.e. can deduce 'down' from the way they perceive the magnetic field) for their local environment.

When the poles reverse then there will be a selective pressure for mutations that have a good correlation between the new orientation of the magnetic field and their idea of 'down'
(Since reversal doesn't happen instantly there will be ample time for the worm population to adapt. It's not like all of the will suddenly bury up and be eaten)
not rated yet Jun 18, 2015
Beautiful work and chemosensory cilia with "sensory ending of the AFD neurons consists of dozens of villi arranged anterior-to posterior (in an antenna-like formation) imbedded inside glial cells or their accessory cells are used for magnetic field detection" .
This TV antenna-like structure shows that induced currents by RF could also directly be detected in others animals, like in our mobile phones ?
5 / 5 (2) Jun 19, 2015
Intriguing. Bacteria are known to have magneto-sensory organelles, using magnetite depositions, for similar purposes in the oceans. Perhaps these neurons, however they work, is a case of convergent evolution.

@DrBaldo: As Vietviet's NASA article mentions (it is good!) there are no large effects on organisms at the time. One can envision that the multipoles of the broken up field provide areas where organisms such as nematods, a many hundred of million years old clade I think (very diverse, most animals of any clade), would go on pretty much undisturbed. But it seems better than that, likely for the reason AAP mention.
5 / 5 (2) Jun 19, 2015
@deudereu: I wouldn't jump to the conclusion that the "antenna like" structure of the AFD neuron has any bearing on its specific functional use, if that is what you mean.

- C. elegans has determinate development, every one of its cells (< 1000!) are accounted for which is one reason why it is a model organism. And the AFD is a multiuse sensor neuron that is part of the circuitry that decides where the worm goes.

"The AFD neuron is part of a neural circuit that underlies thermotactic behavior." [ http://www.jneuro...373.long ]

- Our own optic receptors have organelles with similar antenna like morphology, which maximizes area and so the likelihood that one photon will kick off an amplifying [factor ~1000!] chemical cascade that relies on an internal membrane potential difference and reaches the energy that kicks of a nerve signal over the receptor synapse.

5 / 5 (2) Jun 19, 2015

Something similar can be at hand here, but using the cellular membrane instead, so it can be a generic form for receptors that relies on membranes for part of their function.

- RF and its induced currents doesn't penetrate cellular membranes much due to its natural phospholipid double dipole layer shielding. It has to reach the AFD, and my bet it is too weak to do work using radio signals (nW/m^2 IIRC). Else we would see bacteria evolving to rely on radio signals for metabolic purposes inside cities, and we don't. They do however evolve to attack new organics such as plastics...
not rated yet Jun 19, 2015
I'm not sure we'd have noticed RF eating bacteria, but some have noticed this:
'Crazy Ants' That Eat Electrical Equipment Are Taking Over The Southeast
Read more: http://www.busine...dXU6xuZL
These ants are attracted to AC electric fields apparently.
not rated yet Jun 22, 2015
Electromagnetic fields pass through one another without interaction. That is called "superposition". However, these magnetic fields do react with electrons in their path. It is the electrons that move. Ions can also move, but are much more slugish.

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