GERMANY – How this compass function at the molecular level does was the interest of Prof. Roswitha Wiltschko together with French colleagues. Birds have two senses to their orientation in the Earth’s magnetic field: they measure the strength of the magnetic field using their beaks. The direction information is perceived in the eye. The eyes, which respond to UV light, contain a form of the protein called Cryptochrom. Five years ago, a team of researchers of the Goethe University of Frankfurt, led by Roswitha, suspected that this is most likely responsible for the orientation of the magnetic field.

A cyclic reaction takes place in the Cryptochrom, which consists of a light-dependent and light-independent part. In particular, two radical pairs respond to the Earth’s magnetic field due to its unpaired outer electron resulting in this cycle. Now the German researchers with collaboration with the colleagues from French Universite Pierre et Marie Curie, discovered that this radical pairs is decisive for the orientation of the magnetic field.

In a study of Robins, the birds were exposed to alternatively two different conditions: In the rhythm of a second, researchers switched from either the light or the Earth’s magnetic field. It turned out that the birds can orient also under these conditions on the magnetic field lines of the Earth. This suggests that the “light-independent radical pair” for the perception of the magnetic field lines is responsible. Light is required only to keep the cycle going.

“This is the first proof that the radical pair produced in darkness is critical for the magnetic compass”, said Prof. Roswitha Wiltschko. Since Cryptochrome serve only the perception of light in other organisms, the study suggests there is a particular evolutionary adaptation in birds.

The study was published in the Journal of the Royal Society Interface