“If you don’t know how something works, you can’t really be certain
that you understand how it could have evolved.” — BOB MONTGOMERIE

Trout nose cells
sniff magnetism

Tissue in fish’s snout could explain animals’ compasses

The first demonstration of an animal’s internal compass dates to nearly half a century ago, when experiments showed that caged robins turn when exposed to rotating magnetic fields. Other birds, as well as sea turtles and some fish and amphibians, share this ability.

9 in the Proceedings of the National Academy of Sciences, Michael Winklhofer of the University of Munich and colleagues broke apart olfactory tissue from rainbow trout and bombarded free-floating cells with magnetic fields.

By Devin Powell

Cells plucked from a trout’s snout can swivel like tiny compasses to line up with a nearby magnet. That sensitivity, credited to iron inside the cells, could explain how fish, birds and other animals sense Earth’s magnetic field — a long-standing mystery among biologists.

But the specific body structures behind the sense — which humans either lack or aren’t aware of — have remained elusive. Magnetic fields easily penetrate flesh, so receptors that respond to them could be hidden anywhere in the body.

About one to four of every 10,000 cells responded, spinning in a tight embrace with the rotating magnetic fields. A closer look revealed chains of magnetite glued inside each cell’s membrane. Like a magnetized compass needle, the iron-rich mineral guided the cell around.

“For decades scientists have been searching for the cells responsible for magnetosensation,” says neuroscientist David Keays of the Research Institute of Molecular Pathology in Vienna. “They’re the biological equivalent of the elusive

Recent clues have pointed to nose tissue as the place to look. In fish, magnetic fields can stimulate brain cells that connect to the nasal cavity, as neuroscientist Michael Walker of the University of Auckland in New Zealand and colleagues have demonstrated. His team also found crystals of the magnetic mineral magnetite in nasal tissue from yellowfin tuna.

In living tissue, cells aren’t free to spin in this fashion. But the magnetite’s push could open up pores in a cell’s membrane. Charged particles moving in and out could set off electrical impulses, stimulating the brain. To support this theory, the researchers are looking for the movement of charged calcium in living cells.