The elusive magnetic sense and why worms may be of no help
Magnetoreception, a 'sixth sense' for the detection of magnetic fields, has long been investigated in animals such as birds. A 2015 paper sparked hope that the popular model organism C. elegans might be able to sense magnetic fields. This hope is now shattered by David Keays.
The storks are back. On their migratory routes, they have covered up to ten thousand kilometers to finally home in on the same nests that they have occupied for years. The birds’ remarkable navigation skills rely not only on visual clues but on their phenomenal ability to sense the earth’s magnetic field. Magnetoreception is not confined to birds, it is found in many species, from fish to insects, but just how they do it still remains a mystery.
At the Research Institute of Molecular Pathology (IMP) in Vienna, neurobiologist David Keays has spent the past ten years in search of the sensory organ that perceives magnetic fields. Working with pigeons, his lab was able to prove in 2012 that the widely adopted concept of magnetosensing nerves in the beak was actually wrong - the iron-rich cells were simply macrophages filled with debris. The search was on again.
Since the magnetic sense was so elusive, it seemed like a good idea to also study other species that sport an internal compass – ideally a simple and well-established model organism. A paper by Andrés Vidal-Gadea et al. (eLife, 2015) describing magnetic orientation in C. elegans worms was therefore more than welcome. It described how the tiny nematodes were attracted to a magnet placed in an agar plate in which they were able to move freely.
David Keays had some experience with C. elegans. After all, its development, behavior and brain circuitry are being studied by several groups at the IMP, but no one had been able to elicit a magnetic response from the worms.
Keays and his team decided to replicate the experiments. They were well equipped, since the IMP features a magnetically shielded room and other devices to tinker with magnetism. However, all attempts to reproduce the results of the US-team failed, as they recently reported in eLife (Landler at al., 2018).
An article by Abby Olena in The Scientist now provides a good overview of the efforts of both teams and points to possible reasons for the discrepancies. In any case, the detective story surrounding the magnetic sense continues and we are eagerly hoping for more surprises to come.
"Worm's Magnetic Sense Questioned", The Scientist (2018). By Abby Olena.
"Comment on "Magnetosensitive neurons mediate geomagnetic orientation in Caenorhabditis elegans", elife (2018). By Lukas Landler et al.
"Magnetosensitive neurons mediate geomagnetic orientation in Caenorhabditis elegans", elife (2015). Andrés Vidal-Gadea et al.