Researchers in Texas say they've found the first sensing structure for the magnetic field of Earth ever identified in an animal, a vital clue to understanding how an animal's internal compasses could help it navigate.
Many species including sea turtles, wolves and migrating geese are known to make use of the globe's magnetic field to help them navigate, but exactly how they accomplish it - and where their magnetic compasses might be located - has been difficult to pinpoint, the researchers say.
Now in a tiny worm known as C. elegans, scientists at the University of Texas at Austin have found a microscopic structure sitting at the end of a brain neuron that the worms are using to move about underground.
Given similarities in common brain structure across many species, the structure or something similar to it is likely shared by other animals, says neuroscientist Jon Pierce-Shimomura in the university's College of Natural Sciences.
"Chances are that the same molecules will be used by cuter animals like butterflies and birds," he says. "This gives us a first foothold in understanding magnetosensation in other animals."
In the worm, the structure resembles a nanoscale television antenna, the researcher found.
To test the worms' navigational structure, the researchers obtained samples of C. elegans from other parts of the world to see if they would use their antenna to direct them downward in tubes filled with gelatin, a normal strategy in their search for food.
Local worms from Texas did so, of course, but worms from other regions of the world moved in different directions - in each case, at a precise angle relative to the magnetic field that would have told them up from down in their own part of the world, the scientists have written in the journal eLife.
For example, worms from Australia - at the opposite side of the Earth - moved up, not down, in the tubes.
The magnetic field sensor structure of each worm is finely tuned to its particular local environment, and to the exact orientation of the magnetic field there - but that orientation varies from location to location on the Earth, the researchers explain.
In previous research, other scientists have discovered brain cells in pigeons that could process information regarding magnetic fields, but could not identify exactly where in the pigeons' bodies that information was coming from.
"It's been a competitive race to find the first magnetosensory neuron," Pierce-Shimomura says. "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."
