Researchers find cells that move in response to Earth's magnetic field

Jul 10, 2012 report
Rainbow Trout (Oncorhynchus mykiss). Image: Knepp, Timothy - U.S. Fish and Wildlife Service

(Phys.org) -- For nearly half a century scientists have known that some animals are able to navigate using the earth’s magnetic field and for nearly thirty years, it’s been assumed that at least some of those animals that are able to “feel” the weak magnetic field are able to do so because of small amounts of iron material in their tissue. Now, a team of researchers led by Michael Winklhofera of Ludwig-Maximilians-University in Munich, have discovered a way to find individual cells that respond to a magnetic field in one species of migrating fish. As they describe in their paper published in the Proceedings of the National Academy of Sciences, all it took was the introduction of a rotating artificial magnetic field.

Finding the parts of the body that are able to sense a magnetic field, called magnetoreception, has been difficult because of the nature of magnetism. Like sound or light, it strikes the entire body, but unlike the other two stimuli, it can also penetrate the skin and keep on going, meaning receptors could reside virtually anywhere in an organism. Logically though, such receptors would be more likely to reside in the head somewhere, in close proximity to the brain. In migrating fish, the suspicion has been that a good place for such cells would be inside the nose, as fish seem to follow it as they swim.

To find out if this is the case with rainbow trout, the team took a sample of olfactory epithelium from the snout of one such specimen and placed it inside a ring of rotating magnets. Then they looked at the specimen under a microscope and found individual cells that spun around on their axis following the artificially induced magnetic field. Upon closer inspection of the cells, the team found iron-rich crystals, most likely single-domain magnetite sitting at just one end of the cell, very near the membrane; which makes sense. To cause a spin, the magnetite would need to be at the tip of a cell just as it is on the tip of a needle in a compass. Only a few of the cells were found, leading the researchers to estimate that the tissue likely holds just one such cell out of ten thousand capable of responding to a magnetic field.

Of course the finding doesn’t actually prove that the cells are responsible for the fish’s ability to navigate long distances, but it does seem likely to be the case. The trick now will be to show how cells that move in response to a magnetic field are able to convey a message to the brain.

Explore further: Built-in billboards: Male bluefin killifish signal different things with different fins

More information: Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells. S.H.K. Eder, H. Cadiou, A. Muhamad, P. A. McNaughton, J. L. Kirschvink, M. Winklhofer. www.pnas.org/cgi/doi/10.1073/pnas.1205653109

Abstract
Over the past 50 y, behavioral experiments have produced a large body of evidence for the existence of a magnetic sense in a wide range of animals. However, the underlying sensory physiology remains poorly understood due to the elusiveness of the magnetosensory structures. Here we present an effective method for isolating and characterizing potential magnetite-based magnetoreceptor cells. In essence, a rotating magnetic field is employed to visually identify, within a dissociated tissue preparation, cells that contain magnetic material by their rotational behavior. As a tissue of choice, we selected trout olfactory epithelium that has been previously suggested to host candidate magnetoreceptor cells. We were able to reproducibly detect magnetic cells and to determine their magnetic dipole moment. The obtained values (4 to 100 fAm2) greatly exceed previous estimates (0.5 fAm2). The magnetism of the cells is due to a μm-sized intracellular structure of iron-rich crystals, most likely single-domain magnetite. In confocal reflectance imaging, these produce bright reflective spots close to the cell membrane. The magnetic inclusions are found to be firmly coupled to the cell membrane, enabling a direct transduction of mechanical stress produced by magnetic torque acting on the cellular dipole in situ. Our results show that the magnetically identified cells clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field. This would also explain interference of ac powerline magnetic fields with magnetoreception, as reported in cattle.

Press release

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User comments : 6

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kevinrtrs
1.4 / 5 (21) Jul 10, 2012
Now here we have a signalling element all by itself. But that is totally useless to the fish/organism unless the signal is transmitted and DECODED by some processing unit. Without sucha n interpreting unit, , how would the fish actually make use of the signalling element? Of what survival benefit would that element be without the decoder. Alternatively what would the decoder do with decoding instructions if the element didn't exist? Equally important - how would the one know about the existence of the other if there wasn't an existing interconnection?
It seems like an irreducibly complex setup impervious to "evolutionary" processes.
Herein lies a major headache for evolutionary theory - the very existence of a code that requires a decoding mechanism. How can such an abstract notion arise from pure materialistic processes? To date no such thing has been documented as happening at random in the physical world. If you disagree, simply provide supporting evidence for your assertion.

antialias_physorg
4.6 / 5 (10) Jul 10, 2012
But that is totally useless to the fish/organism unless the signal is transmitted and DECODED by some processing unit.

If you read the article (which I'm sure you didn't) then you would have noticed that it SAYS EXPLICITLY that that is the next thing they will be looking for. One step at a time.

It seems like an irreducibly complex setup impervious to "evolutionary" processes.

Are you really convinced that the structure is useless? Because that means you have just admitted to yourself that there is no god and no intelligent designer - since no intelligent designer would incorporate a useless feature.

To date no such thing has been documented as happening at random in the physical world

You mean apart from every sensory organ on every organism, ever?
And evolution is not random. It's random mutation plus "survival of the fittest" (weeding out the random stuff that doesn't work).
88HUX88
3.9 / 5 (11) Jul 10, 2012
irreducible complexity has been blown out of the water numerous times, even in court http://en.wikiped...District
it has no place in a science forum
Deesky
3 / 5 (2) Jul 10, 2012
@kev,
Now here we have a god element all by itself. But that is totally useless to humans unless the god signal is transmitted and DECODED by some religious processing sect. Without such a religious interpreting unit, how would humans actually make use of the signalling element? Of what survival benefit would that element be without the religion decoder?

Alternatively what would the religion decoder do with decoding instructions if the god element didn't exist?

It seems like an irreducibly complex setup impervious to logical processes.
Herein lies a major headache for religion theory - the very existence of a mystical code that requires a religious decoding mechanism. How can such an fantasy notion arise from pure materialistic processes? To date no such thing has been documented as happening in the real, physical world. If you disagree, simply provide supporting evidence against my god delusion.
C_elegans
not rated yet Jul 11, 2012
KevinRTS - what is your question? It sounds like you're looking for something. Have you tried opening yourself up to observations of the world around us? Are you ready to accept what you find?
and7barton
not rated yet Jul 11, 2012
I enjoyed the scientific observation that fish "Seem to follow their noses". I think if you care to take a look around you, EVERY animal "follows its nose". This may possibly be due to the fact that the nose is always at the very front.