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Worms Know What's Up — And Now Scientists Know Why

Researchers say that inside the head of the worm <em>C. elegans</em>, an antenna-like structure at the tip of the AFD neuron (highlighted in green) is the first identified sensor for Earth's magnetic field.
Andrés Vidal-Gadea
Researchers say that inside the head of the worm C. elegans, an antenna-like structure at the tip of the AFD neuron (highlighted in green) is the first identified sensor for Earth's magnetic field.

In what researchers say is a first, they've discovered the neuron in worms that detects Earth's magnetic field. Animals have been known to sense the magnetic field; a new study identifies the microscopic, antenna-shaped sensor that helps worms orient themselves underground.

The sensory neuron that the worm C. elegans uses to migrate up or down through the soil could be similar to what many other animals use, according to the team of scientists and engineers at The University of Texas at Austin.

The team's work was published Wednesday by eLife.

In contrast to previous breakthroughs — such as a 2012 study on how pigeons' brains use information about magnetic fields, and another from the same year on olfactory cells in trout — the new work identifies the sensory neuron that detects magnetic fields.

"We also found the first hint at a novel sensory mechanism for detecting the magnetic field," says Jon Pierce-Shimomura, an assistant professor of neuroscience who worked on the study. "Now researchers can check to see if this is used in other animals too."

The list of animals that could be studied for their use of magnetic fields is long — and it seems to grow each year. In early 2014, for instance, a study found that dogs who need to relieve themselves of waste prefer to align themselves on a north-south axis when the magnetic conditions are right.

Pierce-Shimomura says his team was surprised to make a new breakthrough in magnetism by looking at worms, which aren't known for their sophisticated migrations.

"It was unexpected that an animal would use the earth's magnetic field to move up and down," he says.

Their experiments included studying how worms from the U.S., Australia, England, and elsewhere behave when they're put in in a lab in Texas.

From the study:

"Well-fed worms migrated up, while starved worms migrated 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."

In particular, the researchers found that Australian worms moved in opposite ways than their kin from England — and they noted that in the Australian worms' home in Adelaide, "the magnetic field of the earth is similar in strength and angle to that in England but differs in the key respect of having the opposite polarity."

We sent Pierce-Shimomura a few questions about the team's work; here are his answers:

What is most unique about your findings?

"This is the first discovery of an actual sensory neuron that detects the Earth's magnetic field. Birds, turtles, butterflies and many other animals can sense the magnetic field for their impressive migrations. But researchers are still searching for the neurons in these animals that sense the magnetic field."

How might other animals detect the magnetic field?

"There is evidence that some animals may use microscopic compasses made of iron, but it remains to be seen what neurons use these hypothetical compasses, so the theory remains unproven. There is also evidence that other animals may use a mechanism independent of iron — instead they might use a special molecule that transiently turns into a compass of sorts when hit with light.

"We still don't know which of these two mechanisms worms use, and/or whether they use a different mechanism. But having identified the actual sensory neuron that detects the magnetic field will expedite this process of discovery."

What applications or further study might this open up?

"I think we can now expect that other animals, especially small insects, may use this to parasitize plant roots and animals. If true, then we might be able disorient these pests with an irregular magnetic field."

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Bill Chappell is a writer and editor on the News Desk in the heart of NPR's newsroom in Washington, D.C.
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