Les foies de pigeon peuvent agir comme des compasses magnétiques via des cellules immunitaires riches en fer

Homing pigeons trained to fly 20 kilometers to an aviary in Radolfzell, Germany, became completely lost when researchers used a drug to selectively kill macrophages in their livers. This disruption suggests that these iron-rich immune cells may serve as a primary component of the birds' magnetic navigational sense.

Iron-Packed Macrophages and Nerve Endings

The hypothesis rests on the behavior of macrophages—the immune system's "vacuum cleaners"—which recycle iron from dead red blood cells. While these metal-rich cells typically congregate in the spleen in humans, researchers found that in homing pigeons, they are heavily concentrated in the liver. Using extremely powerful magnetic fields, the team demonstrated that these cells are packed with a specific form of iron and, crucially, they abut nerve endings, providing a potential pathway for magnetic information to reach the brain.

Martin Wiketski of the Max Planck Institute of Animal Behavior, a co-senior author of the study, suggests this mechanism might not be limited to pigeons but could extend to bees, mammals, and bats.

Skepticism Over Superparamagnetism

Despite the findings, the scientific community is divided. A landmark 2012 Nature study previously suggested that macrophages contain the wrong kind of iron to respond to Earth's relatively weak magnetic field. To counter this, the new study points to "superparamagnetism," a quantum mechanical phenomenon that could heighten the iron's responsiveness.

However, geobiologists like Joe Kirschvink from the California Institute of Technology and biologists such as Carl Meyer from the Hawaii Institute of Marine Biology remain unconvinced. They argue that current biophysical models for superparamagnetic magnetoreceptors have hit a dead end and that there is little evidence superparamagnetism could sufficiently notify a neuron in a natural environment.

Whether this discovery represents a genuine breakthrough or another failed attempt to solve the mystery of biological magnetoreception remains to be seen as researchers attempt to map how these cells translate orientation into geographic data.

Source: A new study says homing pigeon livers act like compasses. Other experts aren't so sure
Domain: scientificamerican.com