A messenger substance for the magnetic sense
How animals perceive the earth's magnetic field is a great mystery. The protein ErCRY4 seems to play a central role.
One of the greatest mysteries of sensory biology is the sense of magnets: the ability of many animals to perceive the earth's magnetic field and use it as a compass. Birds, sea turtles, fish, crustaceans and insects use it to navigate over short or long distances. So far, however, it is unclear on which physical mechanism the field perception is based.
Migratory birds have magnetically sensitive proteins, so-called cryptochromes, in the retina of their eyes, which are considered to be a crucial component of the magnetic sense. However, until now there has been no evidence that their mode of operation and their sensitivity make it possible to feel the extremely weak magnetic field of the earth. A team led by Jingjing Xu from the Carl von Ossietzky University of Oldenburg has now provided the evidence in laboratory tests, bringing us closer to solving the mystery.
There are currently two main hypotheses as to how animals perceive the Earth's magnetic field. One says: If an organism changes its orientation in the field, magnetite crystals (Fe3O4) inside exert a rotational force on sensory cells, which register mechanical forces. For example, if a migratory bird flies a curve, the crystals rotate with it in the outer field. Since they strive to align themselves along the field lines, they experience a force that they could transmit to sensory cells as torque. This, in turn, could open or close ion channels located in the cell membrane, allowing for sensory perception.
According to the other hypothesis, cryptochrome proteins that absorb photons of light and are thus energetically excited form magnetically sensitive chemical intermediates called radical pairs…
