Obviously, none of these animals, which range from invertebrates to mammals, rely on Google Maps. Instead, they seem to be reading some invisible clues in the environment. People throughout history have tried to solve the mystery. Now researchers are being drawn to some powerful clues.
Starting some 50 years ago, scientists began to realize that some animals might come equipped with a biological compass that can read the Earth's magnetic field.
Since then, this once-controversial hunch has been proven correct for many species. Its underlying mechanism, however, has remained unknown. But that may be changing.
The main five senses use organs like the eyes, ears and nose to see, hear and smell. Now researchers in China believe they've decoded a sixth sense called magnetoreception. Its secret lies in a rod-shaped protein structure that can spontaneously align to the Earth's magnetic fields, Can Xie and his colleagues from Peking University recently reported in the journal Nature Materials. The team found it in the retina of a pigeon, a location that had already been connected to the magnetoreception sense.
Using state-of-the-art genomic and protein analysis equipment — some of which was developed by GE Healthcare Life Sciences — the team focused on a protein they call MagR. This protein is capable of aligning with magnetic fields after coupling with a light-sensitive protein called Cry.
They found the complex molecules in fruit flies, pigeons, butterflies, rats, whales and humans, though they caution that it is still unknown whether animals actually use it for magnetoreception.
But seeing it across species — many of which are known to rely upon sensing magnetic fields — allowed Xie to form a hypothesis. “The nanoscale biocompass has the tendency to align itself along geomagnetic field lines and to obtain navigation cues from a geomagnetic field,” Xie told the Guardian. “We propose that any disturbance in this alignment may be captured by connected cellular machinery, which would channel information to the downstream neural system, forming the animal’s magnetic sense.”
The article has drawn considerable interest from the research community. Michael Winklhofer, an Earth scientist at Germany's Ludwig Maximilian University, will perform follow-up research on the Chinese team's findings to verify them. He told Nature that the discovery of MagR “appears to be a major step forward towards unravelling the molecular basis of magnetoreception.”
Not so fast, say others. “It’s either a very important paper or totally wrong. I strongly suspect the latter,” David Keays, a magnetoreception specialist at Austria's Institute of Molecular Pathology, told Nature. “One has to ask whether in vivo, at physiological temperatures, MagR is capable of possessing magnetic properties at all. If MagR is the real magnetoreceptor, I’ll eat my hat.”
One part of the research that isn't in question is the Chinese team’s equipment. They used a prototype of a GE tool called a size-exclusion chromatography column, which allowed them to purify the Cry/MagR protein complex.
This column, which was designed for use in biological and pharmaceutical research, allowed the group to accurately separate the complex from other molecules quickly. From this step, the team was then able to take pictures of the complex with an electron microscope.
The size-exclusion chromatography column, which works on the principle that molecules in a liquid will pass through porous media within the tube at different speeds based on their size, “proved to be critical in obtaining a homogeneous sample for (electron microscopy) structural determination,” the authors wrote in their acknowledgments.