In the era of smartphones, getting home has never been easier, but for animals who have escaped the grasps of digital dependency, some pretty nifty adaptations for navigation have emerged. Some of the greatest migrators are birds, making enormous journeys year on year to nesting grounds and warmer climes, and it’s long been suspected that the Earth’s magnetic field has played an integral role in helping them work out where the hell they’re going. Now, new research believes to have cracked the mechanism that underpins this magnetic sensor, revealing that a lot goes into a birds’ eye view.
Published in the journal Nature, the study’s insights hinged on a first-time achievement in producing the photoactive protein cryptochrome 4 (CRY4) successfully carried out by the study’s first author Jingjing Xu, a doctoral student in Henrik Mouritsen of the University of Oldenburg’s research group. This molecule is found in the retinas of birds but until now had never been produced in a lab. Xu was able to make CRY4 of several bird species by extracting its genetic code and combining it with bacterial cell cultures who would happily churn out an identical copy of the birds’ proteins.
Once the team had cryptochrome 4 at their disposal, they employed the help of magnetic resonance and optical spectroscopy to uncover the protein’s secrets and establish whether or not it was indeed sensitive to Earth’s magnetism. They exposed the CRY4 proteins of European robins, who are night migratory birds, to enormous magnetic fields and were able to observe that it was indeed magnetically sensitive in-vitro. The retinas of chickens and pigeons (two non-migratory birds) were far less sensitive. The difference between the birds’ retinal proteins was pinned down to site-specific mutations in the robin’s genetic code which shaped the roles of four flavin–tryptophan radical pairs within CRY4.
Magnetic sensitivity in the bag, they next wanted to establish how this retinal protein might actually relay information to the bird, after all, it’s no use having a compass if you can’t see it. Looking at the behavior of the robins’ CRY4 on a computer, they were able to see that field changes are reflected in the movements of singular electrons within the protein, an observation in science so small it falls within quantum mechanics. These minute movements alter the protein’s reaction products which are picked up by neurons.
If you’re thinking quantum movements within specific retinal proteins of migrating bird species sounds like a bit of a headache to research, then it seems you’re probably right. Mouritsen himself told Gizmodo that the research hasn’t yet proven unequivocally that CRY4 is the defining magnetic sensor in migratory birds, and that reaching a definitive conclusion could still take some time owing to its complexity. “I can’t guarantee you any timeline of that because it’s very, very challenging,” he said.
