Migrating Arctic Terns at Carate Beach, Costa Rica. Scientific American writes: “The biocompass—whose constituent proteins exist in related forms in other species, including humans — could explain a long-standing puzzle: how animals such as birds and insects sense magnetism.”
Photo Credit & Source: Playalapa.com
An article, by David Cyranoski, in Scientific American, first reported in Nature, says that researchers at Peking University in Beijing, China, might have found the piece of the puzzle on how animals navigate the earth’s weak magnetic field: a rod-shaped complex of proteins, CG8198, which have been named MagR, for magnetic receptor. This protein forms a part of the animal’s biocompass, or internal biological navigation device.
In “Long Sought Biological Compass Discovered” (November 17, 2015), Cyranoski writes:
The biocompass—whose constituent proteins exist in related forms in other species, including humans—could explain a long-standing puzzle: how animals such as birds and insects sense magnetism. It might also become an invaluable tool for using magnetic fields to control cells, report researchers led by biophysicist Xie Can at Peking University in Beijing, in a paper published on November 16 in Nature Materials (S. Qin et al. Nature Mater .http://dx.doi.org/10.1038/nmat4484; 2015).
“It’s an extraordinary paper,” says Peter Hore, a biochemist at the University of Oxford, UK. But Xie’s team has not shown that the complex actually behaves as a biocompass inside living cells, nor explained exactly how it senses magnetism. “It’s either a very important paper or totally wrong. I strongly suspect the latter,” says David Keays, a neuroscientist who studies magnetoreception at the Institute of Molecular Pathology in Vienna.
Many organisms—ranging from whales to butterflies, and termites to pigeons—use Earth’s magnetic field to navigate or orient themselves in space. But the molecular mechanism behind this ability, termed magneto-reception, is unclear.
Some researchers have pointed to magnetically sensitive proteins called ‘cryptochromes’, or ‘Cry’. Fruit flies lacking the proteins lose their sensitivity to magnetic fields, for example. But the Cry proteins alone cannot act as a compass, says Xie, because they cannot sense the polarity (north–south orientation) of magnetic fields. Others have suggested that iron-based minerals might be responsible. Magnetite, a form of iron oxide, has been found in the beak cells of homing pigeons. Yet studies suggest that magnetite plays no part in pigeon magnetoreception.
Xie says that he has found a protein in fruit flies that both binds to iron and interacts with Cry. Known as CG8198, it binds iron and sulfur atoms and is involved in fruit-fly circadian rhythms. Together with Cry, it forms a nanoscale ‘needle’: a rod-like core of CG8198 polymers with an outer layer of Cry proteins that twists around the core (see 'Protein biocompass'). Using an electron microscope, Xie’s team saw assemblies of these rods orienting themselves in a weak magnetic field in the same way as compass needles. Xie gave CG8198 the new name of MagR, for magnetic receptor.It would seem that this means that animal navigation is due, at least in part, to biology or, more precisely, to biochemistry and its determination that a rod-shaped complex protein aids in the long treks that so many species make before the onset of winter. I am not sure if the science behind this theory is valid (it sounds overly mechanistic), but animal migration in itself is an important question worthy of scientific research. That this happens regularly and predictably is comforting; it is also a sight to behold. So many species migrate during the winter, from birds to butterflies. You can almost set your seasonal calendar by their migratory patterns.
For example, the Canada goose (Branta canadensis) have already left here, have already made their migratory flight southward (as far in some cases as the southern U.S.). This continues to be a wonder to see, especially their V formations with the leader giving honking orders, or so it seems down here. They will return in the spring, and their honking sounds is a beautiful noise for tired Canadians weary of winter.
The gray whale (Eschrichtius robustus) migration is currently underway, from the Arctic to Mexico’s Baja Peninsula, a journey of 8,000 km (5,000 miles)—it holding the record for the longest migratory journey by a mammal. Mexico is also the primary destination of the monarch butterfly (Danaus plexippus), which travel the 5,000 km (3,000 miles) from Canada and the northeastern U.S. to their “ancestral wintering grounds in the volcanic mountains of central Mexico.”
Then there is the Arctic tern (Sterna paradisaea), a small seabird that holds the record for the longest winter flight southward—from Greenland to Weddell Sea on the shores of Antarctica—and then returns northward in summer for a total round-trip of almost 71,000 km (44,000 miles). That is some dedication and perseverance for a bird that has a body mass of around 100 grams.
For more, go to [ScientAmer]