Cryptochromes are a common group of light-sensitive molecules that exist in bacteria, plants, and animals. In addition to regulating circadian rhythms, these specialized proteins enable certain animals, such as birds, insects, fish, and reptiles, to sense magnetic fields, allowing them to perceive direction, altitude, and location. Humans are incapable of magnetoreception. Some mammals, like bats, mole rats, and mice, appear to have this sense, but the extent of this capacity among other mammals is largely unknown.
Now, in the first study of its kind, researchers from the Max Planck Institute and several other institutions have investigated the presence of the mammalian version of this molecule, called cryptochrome 1, in the retinas of 90 animal species. Researchers found this molecule in the blue-sensitive cones of dog-like carnivores, such as dogs, wolves, bears, foxes, and badgers, but not in the eyes of cat-like carnivores, such as cats, lions, and tigers (felines have their own unique way of looking at the world). Among primates, researchers discovered the presence of cryptochrome 1 in orangutans, the rhesus macaque, the crab-eating macaque, and others. The details can now be found in Nature Scientific Reports.
Though it’s considered a “sixth sense,” magnetoreception is tied to an animal’s visual system. Magnetic fields activate cryptochrome 1 in the retina, which the animal “sees” as the inclination of magnetic field lines relative to the Earth’s surface. Because the active cryptochrome 1 is located in the light-sensitive outer segments of the cone cells of the mammals, the researchers suspect that it’s assisting with magnetoreception, and not circadian rhythm management or some other visual capacity.
It’s not immediately obvious how mammals like dogs and primates use their magnetoreception, but foxes may provide a clue: When hunting, foxes are more successful at catching mice when they pounce on them in a northeast direction. For primates, this built-in compass may help with bodily orientation, or it could be a vestigial evolutionary trait that’s largely unused.
The next step will be to prove that these mammals are truly leveraging the power of cryptochrome 1, or whether the molecule is performing other tasks in the retina.