Birds, bees, whales, and turtles all use the Earth’s magnetic field to guide their behaviour. Now scientists have learned much more about how. Maria Armoudian speaks with Andres Vidal-Gadea about what has been discovered.
Andres Vidal-Gadea is an Assistant Professor of Molecular Neuroethology at Illinois State University. He is an expert in animal molecular behaviour.
This interview has been edited for clarity and length
Maria Armoudian: This research that you have done related to the magnetic field of the Earth and how all these species use it is quite fascinating. Your article starts with sort of a broad stroke about the purpose of the magnetic field itself for the Earth but also for the animals. Do you think we could start with a bit of Earth magnetic field 101?
Andres Vidal-Gadea: The inside of the Earth is made of molten material and this is turning all the time and pretty much like an engine is generating a huge magnetic field that expands far into space. This magnetic field as far as we know protects life on Earth from harmful radiation from the sun and it also provides a very constant and reliable cue for navigation that animals can use to orient themselves.
MA: Different kinds of animals use this. We know birds use the magnetic field to orient themselves when they migrate. What else? What are the other animals that use it?
AVG: Animals like bees, for example, and animals like mole rats, mammals, especially migratory animals like birds and whales use the magnetic field. In fact, it was only because we weren’t looking before that we didn’t see how many species are capable of using the Earth’s magnetic field to navigate. I originally got started on this on a sea slug that lives on the bottom of the sea and apparently uses the magnetic field to find its way around, so these things are all around us.
MA: So do you suspect as the scientist studying this that really all species rely on the magnetic field as a source of information?
AVG: I don’t think all species perhaps use the magnetic field but I think that the list is probably much greater than we anticipated. One of the things that I was very surprised to find out was initially these tiny little worms that live in the soil will care about the magnetic field because normally people think of larger more mobile organisms using the magnetic field. That kind of opened the possibility that maybe there are all kinds of little animals in the ground that are using the magnetic field all the time and we didn’t pay attention to it before. I think that in my mind at least, animals that need to navigate in their environment are the ones that may use it, especially animals like the worms that live in an environment that is devoid of sensory information perhaps. They can use the magnetic field to help them find their way around.
MA: So birds of course, butterflies, bees, you mentioned whales, your article mentioned wolves. How would wolves even detect the magnetic field?
AVG: There are a couple of ways in which people believe animals can detect the magnetic field, one of them relies on tiny little intercellular functions inside certain cells of organisms and this is certainly the case for some bacteria and people have identified particles in bees and in other animals. The second way that people believe animals can detect the magnetic field is with some specialised photoreceptors in their eyes, and this applies to many birds and other species. The idea here is that perhaps a photoreceptor cell in the retina of a bird may be able to see the magnetic field just like we can see colour, and from that inform the animal which way they need to go. And so I think that in the case of the wolf and other mammals that people looked at that is the idea that right now they have it. But this is one of the things right we can do experiments that inform us that an organism can orient to magnetic fields but it is a very different thing to find out where the cells that detect the magnetic field or how these animals are detecting, that is what makes it really difficult. And that is one of the things that the little worm we look with comes in really handy because it only has one thousand cells all together so it makes it a lot easier to count.
MA: let’s talk about what you found and how you conducted the experiment. You wanted to see how this worm operates with the magnetic field so you used a means of manipulating the magnetic field. Why don’t you tell us the process and then let’s talk about what you discovered?
AVG: Originally it was a very simple idea. I came across an article where some scientists indicated that they found these tiny magnetic particles inside the worm. And having been working with this as an undergraduate I was thinking ‘well, if they have these tiny particles maybe they can detect the magnetic fields’. So the first experiment that I did was simply to put a magnet next to a plate which had worms in it and after a few minutes we noticed that the worms went over the magnet and right then and there we realized ‘Wow this animal can definitely tell there is a magnet over there’. So after that we tried to be more sophisticated so we built a magnetic cage, and this is just a box that allows us to control the magnetic field within it, so we can dial any kind of magnetic field that we want. And sure enough we started testing the animals in there and we noticed that in this magnetic cage the worms didn’t just go along with the magnetic field but they rather chose a particular direction to it. And once we started thinking ‘Why would this worm go at a particular angle to the magnetic field?’ And after a while scratching our head we looked at what these worms came from and we realised these worms came from England, and if these worms were in England in the soil the direction that they were going to the magnet was the same direction that would take them up or down in the soil if they were migrating to the Earth field in England.
MA: You had Australian worms, you had British worms, you had Hawaiian worms, and you had Equatorial worms and they all did different things which is I think quite fascinating. Can you walk us through that?
AVG: Yeah, so if you think of an animal that can orient to the magnetic field, the great majority of animals, people immediately think of birds that migrate north or migrate south. These are animals that move horizontally so to speak in the environment. Now the magnetic field it has a horizontal component and we use it to go north, east, west, south, these are the directions we are familiar with, but the magnetic field also has an angle to it to the ground and so you can imagine the magnetic field being perpendicular to the soil if you were in the North Pole or the South Pole and being horizontal or parallel to the soil if you were in the equator. And we knew that there were worms isolated from all parts of the world, there are worms isolated from something like one hundred countries and so we could easily get a hold of these animals and bring them to a lab and then we test them. So the idea was the following: if the worms use the magnetic field like a bird to migrate horizontally then worms from the equator should be able to do this no problem because in the equator the magnetic field is horizontal and parallel to the ground. However, if worms use the magnetic field to go up and down then worms from the equator may not be able to do this because in the equator the magnetic field is not vertical. And this is exactly what we found, we found that worms that were close to the equator did not really orient to the magnetic field, but worms that were from the northern parts of the world, they did this very well and worms that were from the southern hemisphere like Australia were also able to do this. The trick was that in the northern hemisphere the magnetic field is pointing down, while in the southern hemisphere the magnetic field is pointing up. So the polarity is reversed and according to that we also saw that Australian worms were moving at the opposite direction than British worms would.
MA: You also noticed that if they were hungry, they reacted differently?
AVG: Yes. This was a headache at first. The first time I did this it worked beautifully and then I tried to do it again and then they went away from the environment. And I was trying to understand why sometimes the worms would go one way and sometimes they would go the other way. Clearly, they could tell there was a magnet there because otherwise they would just go in random directions. But in this case, they knew but they were just trying to confuse me and it took a while to realise that it only takes fifteen minutes for a happy and healthy well-fed worm to start to feel hungry and at that point they decided to go in the opposite direction. And so once you figure this out then it was easier to do the experiment, but for a while we just didn’t know what was going on there.
MA: So you had to starve some worms?
AVG: Yes, so eventually we decided to either run the experiment with the animals that were just out of the food or we could choose to just put them away from food for fifteen-thirty minutes and then run the experiment and that did the trick right, then the worms would go consistently towards the magnet or away from it depending on whether they were hungry or starved. And, of course, we didn’t know why they would do that and it wasn’t until we measured where the worms were from and the angle at which the magnetic field enters the Earth in England that we realized that in fact what they were doing was kind of going in an upwards direction if they were well-fed, and in a downwards direction if they were hungry. So we don’t understand exactly why that is but it looks like if the worms are hungry they tend to burrow down into the soil and when they are well-fed they tend to burrow upwards.
MA: Has there been research that ties humanity to magnetic field effects?
AVG: There have been some preliminary studies trying to find out if humans can detect the magnetic field or who are affected by it…People have put humans in big, dark warehouses and they have had somewhat kind of conflicting results. So it hasn’t been consistently proven or disproven that humans can detect the magnetic field. I can tell you that some of these magnetic particles that we find in all these animals that detect the magnetic field, people have found those in the brain of humans as well. And some of these receptors that birds have and some of the molecules that people believe are implicated in seeing the magnetic field, they have found some of this in humans as well. So I think that we have the hardware to do this. Now, whether we do it, I don’t know. It could be a combination of things right, modern humans we are extremely good with our eyes and finding our way around using our sense of vision and for the most part we don’t really need to migrate great distances anymore like a bird or a turtle may have to. We are pretty much set and we are not engaging this huge migration so perhaps we have it but we just haven’t had to use it for a long time.
MA: Finally, I was wondering about whether or not technological changes that humans have made if they alter the ability to detect any kind of magnetic force from the Earth because of the use that humanity has put with magnets, like using magnets in all kinds of technological products?
AVG: I think that is certainly a possibility and people have started to look into that. I am sad and at the same time happy [that] I can’t see magnetic fields because we definitely surround ourselves with them and if we could see them, we would probably be blinded by them. People have started to notice that even powerlines that generate any kind of electricity, any wire in your house that conducts electricity will create a magnetic field. So I definitely think that we have the ability to change how animals navigate their environment and how they go about their business by putting out this huge magnetic fields all around us.
MA: Where do you think your research is going to go next?
AVG: At the moment we discovered this cell that can detect the magnetic field in this little animal and at the moment we are working to find out how does this cell converts magnetic energy into neuronal information. There has got to be some moving parts in this little cell that are transforming one kind of energy into the other, and we believe that possibly the mechanism by which this takes place is probably going to be repeated in many other species. So we are looking into that. And another thing I have some students working on is, we want to know what happens if you withdraw the magnetic field from around animals, people are trying to make plans to travel far into space and far away from the Earth’s magnetic field where all life has evolved. So we are growing animals in a zero-magnetic field chamber and then we are trying to see what happens to the animal when that takes place.
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