Scientists propose electromagnetic induction as basis for magnetic sense
Many animal species can detect magnetic fields, a sense that enables them to navigate over long distances. How this sense works on a cellular and molecular level, however, remains unknown. IMP scientists from the lab of David Keays now re-visited a 19th century hypothesis - and propose that the basis for the magnetic sense in pigeons lies in electromagnetic induction. Their work was now published in the journal Current Biology.
From fish to birds, from mammals to reptiles – many vertebrate species, especially migratory ones, navigate with the aid of the Earth’s magnetic field. Animal behaviour provides clear evidence for the existence of a magnetic sense, but it remains unclear which sensory cells allow the detection of magnetic fields. In their long-standing quest to clarifying this, scientists from the lab of David Keays now turned to a hypothesis first proposed in the 19th century.
In 1882, the French biologist Camille Viguier suggested that when birds move through the Earth’s static magnetic field, voltage is induced within the conductive endolymph in semi-circular canals in the inner ear. As this voltage would vary dependently of the canals’ positions in relation to the inclination and polarity, it would provide a physiological basis for sensing a magnetic field and deriving reference points for navigation from it. Keays and his team now explored this hypothesis using pigeons as a model organism.
In pigeons, scientists had already demonstrated that a certain magnetically induced neuronal activation does not depend on light. Building on this, Keays’ lab showed that low-powered magnetic stimuli of 150 microtesla were sufficient to induce electric fields within the range of physiological detection – and that the molecular machinery required for such a detection can be found in the inner ear canals of pigeons. Using a marker for neuronal activity, the scientists could also show that exposing pigeons to magnetic fields activates the caudal vestibular nucleus, a brain region responsible for processing positional information. Finally, the scientists found a type of voltage-gated calcium channel in the pigeon’s inner ear that is known to mediate electroreception in skates and sharks.
Taken together, Keays and his co-authors believe that they found compelling indications for electromagnetic induction as the mechanism behind the magnetic sense. The data they present offers an alternative to previously favoured research lines, which had focussed on light-based or biogenic magnetite mechanisms.
S. Nimpf, G. C. Nordmann, D. Kagerbauer, E. P. Malkemper, L. Landler, A. Papadaki-Anastasopoulou, L. Ushakova, A. Wenninger-Weinzierl. M. Novatchkova, P. Vincent, T. Lendl, M. Colombini, M. J. Mason, D. A. Keays (2020):
“A Putative Mechanism for Magnetoreception by Electromagnetic Induction in the Pigeon Inner Ear”. Current Biology. https://doi.org/10.1016/j.cub.2019.09.048