 So, as a final speaker before lunch, I've got from the university, and she's talking about the wonderful title, Navigating to the North from land. It's a famous spot of the day between you and lunch, but I actually did my very first, but my whole introduction, I would say, into the scientific community was done in a collaboration with Mike Land and also Donald Nielsen that spoke earlier today, and that really then inspired my whole scientific career. I'm still going in and out, but I'm still on the very same scientific path in the same subject, so to say. So this was a great inspiration to me, so I would like to take you on a journey from land to the stars to see what that inspired me to do. I will start actually talking about this first study that I did now quite many years ago. And we will be staying and talking about navigation in the dark throughout this tour. And of course, if you're out there navigating finding a way at night, there are some things that you can use to stay alive. For example, use the moon, sand hoppers do this to find a way up and down the shore. And many animals also not that many actually the birds are well known to use the stars for example, but there is also a pattern in the sky that you and I cannot see. And that is the pattern of polarized light that forms around the sun for the moon. The rest much of this talk is going to involve polarized light. I want to make sure and remind all of you exactly what polarized light is and how it's formed, but that otherwise before it's going to be very boring, I think so. When the light ray of light comes from the sun, it's completely improvised that is what you see here. That means that it's vibrating in all different directions as it travels through the space. And then if you let the light pass through a polarizing filter, you can orient it so that you will only have one direction of light by that scene. If that is vertical, it's vertically polarized light. And you can also then rotate this polarizing filter, and then you will get for a sort of polarized light. This makes no difference. We can see the intensity of light. We can see the color of light, but we can't see the polarization direction of light. This is ever something that many, many animals can do, including, for example, the insects. And on the sky, this pattern of polarized light is formed due to scattering and reflection that have also polarized light. And we get this polarization patterns formed around the moon or the sun. These ones are very good to orient by because if there are clouds in the sky, you can no longer see the moon or the sun. For example, you can still be these dye white patterns and orient to them. So my whole journey actually started in collaboration with this little spider. What is about this being its gray, its brown, you wouldn't really pay much attention to it. Neither did Don, as it turns out, because he brought this by mistake into the lab looking for a completely different spider at that time. But what then brought our interest was its strange eyes on the back of the spider. So here you see two of the spiders eyes that are looking quite unusual. When we shine a light on them, they will shine back. That itself isn't very common. This is also what you see in cats on the road, for example, as your headlight points towards the cat. It will absorb the light once as it goes into its eye, then it has a mirror at the back of its eye called a tepidum that reflects the light out again. So the photoseppers can absorb the light a second time. Thereby they can catch more light. This is the very common thing that we find among the nocturnal animals. And indeed, this spider is also nocturnal. It becomes active in the evening and stops being active in the morning. They have the same trick. They reflect the light to increase their sensitivity. So that wasn't a strange thing with these eyes. But what was very unusual is that when we look at the eyes, we see the structures here. Those are actually at the very bottom of the eye. Normally when we look at an animal, we don't see what they have at the bottom of their eye, but there is a lens there to reflect the light. These eyes here are actually more covered, more like a window, which means these eyes will not form any images. It's an eye that cannot see spatial structures because it really hasn't got a lens that will reflect and focus the light. Because of this, they have a very, very big visual field. They're going to collect light all over the sky pointing upwards. This is not what is strange. Oh, thank you. So I've got a googling what I'm saying. So that was not what was unusual, but the thing was also, apart from that they could see anything with their own sense of work, was also that when we put a polarizing filter above these eyes, this eye is really bright where this eye is dark. That is because the reflection from this eye is highly polarized in this direction and the reflection from the other eye in the other direction. So we blocked that. If we now rotate the polarizer by 90 degrees, the opposite is seen. So we have here a system that reflects highly polarized light. So if we then looked, we then looked into light by electrophysiology and apology and so on, and we couldn't see that the photoreceptors in each eye were also highly sensitive to polarized light. So deep focus sectors responded to light in this direction and in this eye to light in this direction here. This means that this spider is under polarized light that we have a lot in the sky. In this direction, the right side is going to give a very strong signal because it's highly responsive to this. And it seems also the reflection is much brighter than in the other eye. It's going to give a much stronger signal. Again, if the spider rotates, then under this condition here, this eye is going to be a very strong output. Logically now, if light is polarized in this direction, both eyes will respond the same. And this is how any engineer and obviously spider would define the perfect analyzer of polarized light. So these eyes actually were not used for seeing at all in the usual sense of the word, but as Dharma said, there are many ways to use your eyes. But instead, this was a conference organ. So they were using these two eyes to analyze the proliferation pattern in the sky and finding their way back home. Because these spiders have a little silky nest that they go out from and then they need to find the way back home. We could demonstrate the need for polarized light in the lab because if you didn't give them polarized light to orient by, they never found their way back home again. So of course, you want to show that these animals have these abilities using what is given to them in the natural world. The perfect experiment to do this is that you bring out the polarizing filter that polarizes light that I showed you in the beginning. You place it under the celestial polarization pattern in such a way that the artificial rotation rotates the polarization direction. So a spider that navigating for example running parallel to this direction of polarization, it would then have to turn or we have rotated it and then it would when it came out on the natural sky go back to its original direction of traveling. Super exciting experiment. The spider said no. I'm not going to participate in this experiment. These spiders were horrible to work with. They were so shy and so nervous that we couldn't even be in the room when we were doing the experiments. Definitely not placing a polarizing filter over this animal. At that time, there were no other animals known to use the polarization pattern forward around the moon. It is extremely dim, so it is very difficult to do this. It took four years until this experiment could be done on a totally different organism. So here comes the filter. Instead of a spider, it was put down over a ball rolling down the top. These ones are way more cooperative than the spider. So it comes out here again under the open sky and you see it's beautifully turning back its original direction travel. This is actually one of the two films on an animal orienting the polarization pattern of the moon because it's still the only animal that we know that is able to use and steer by the polarization pattern from the moon. I'm a hundred percent convinced there are so many more animals that can do this. But just like the spider, they're very difficult to work with in the dark as well. So I moved from working with spiders to working with insects. And this is just a demonstration of what you can do with these four animals. We can actually brush the world around them, we can shield the wind, we can stop them every 50 centimeters to understand their comfort systems. And this little guy is just keeping its pores and rolling at its own speed, which opens up for a wonderful repertoire of behavioral experiments that you can expose them to. Why then do they go that straight? Well, they're exposed to both violence and theft in their world. So if they have a diamond ball, these animals, they will have to do their best not to use it again. So here you can imagine that there is a diamond pile over here, where this diamond ball has been made. All the beakers want to do, they don't have a home. They want to get away from the diamond pile, because this is where all the shit happens. They are going to get their food stolen, because this is their food. So they hold the straight bearing to maximize the distance from the diamond pile the whole time. And eventually they find a good spot to dig down. They do so, they consume the diamond ball, then they fly out again after a few days, find a new diamond patch, and it all starts over again. So to steer straight, they rely on a compass that is obviously reading the polarization pattern from the moon. Luckily, there are also, there are thousands of diamond species, and we can work with the dejective ones and maternal ones and twilight ones. And a very, very good way to learn to understand the visual systems of animals is to compare their different solutions to living during the day or living during the night. And since these are very closely related, we can also just really closely compare them and see what morphological adaptations they have to do well with the environment where they're normally active. Beetles, here you see this is a beetle head from above. These here are its two eyes, most insects have two compound eyes, but if we rotate this beetle head, you will see that they also have two eyes and the underside. So most young beetles have four eyes rather than two. And the upper region here of the eye is where they analyze the pattern of polarization in the night sky. They don't have the luxury as of the spiders having eight eyes so they can use two for conversation analysis. They here incorporate that in their normal eyes, so to say. When we look at this range of animals, we find that the expected adaptation that a deactive beetle is going to have a smaller eye than a twilight-excited beetle that will be bigger eyes to collect more light. And then the truly, you know, parallel beetles are going to have even bigger eyes to collect even more light. One of the things we were noticing when we were working with these animals was that some of them had these beautiful facets that you usually see in these eyes and then some of them have this totally smoothed the eye. We saw that in a few of the nocturnal ones and I was at the conference and ended up in a pub together with my grand. And I thought, if I now have Wikipedia of animal vision next to me, I'm going to ask him, you know, why does he think that his adaptation is here? So he made me drawing on a Serbia in the pub and he said that he thinks that when the facets have higher curvature, they're going to shield the light from each other. So this would be a true adaptation, another adaptation to nocturnal vision. So to decide if the animals you're working with are nocturnal, deactive, or corpuscular sounds fairly easy, but it's actually quite hard. There's very literature that is really pinpointing exactly when the animals are active. So because that is actually a very, it takes a long time to look at this. Oh, that's not the thing. Claudia Tocco there, a researcher in my lab, she therefore spent actually several days and nights in the field, emptying a trap every 30 minutes to really really see exactly when our mother's features are active so we can get a good range of the life levels they're active under. And you know, getting up every 30 minutes is a known torture method. So these were the really, really heroic effort on her part, where we can now just pick the animals and look at the visual system, depending on exactly what they're acting. And what we saw was indeed that we find a smooth eyes only in the maternal animals, as predicted in the pub. And we are all the ones that have fester to active in the day. So it is an adaptation to being maternal. And what is really exciting is that one of the big tools, the small one that lives during the night is the only one that has of the maternal ones. So we hope that this one will guide away into understanding this adaptation. So, if you're active at night, we've spoken a lot about polarized lights now. How do you demonstrate this animals also using the moon then. Well, we can do it in the same way that we can show that most by using the sun. It's just easy to show you how we do it with the sun and with the moon. So this is me here with a mirror in this alien PhD student of mine, that is holding a shaving board. And when the beetle is rolling like this, it can for example decide I'll hold the sun or the moon on my left side, and then it can roll straight. But if we now mirror the sun or the moon with a mirror, the beetle comes left side, all of a sudden it's in the mirror. It's now 180 degrees off in dome head. So it needs to rotate back, get the sun back on the left side, and thereby continue rolling straight. This is a classical experiment within orientation research that still shows us so much. These animals now have a mirror image, it's moving left this direction. Then gets the real sun goes right. And then we can mirror the poor guy again. It just clearly shows us that they are really relying on the sun. And we can do this. And I'm not kidding. We can do this for half an hour. They will just go back and forth. And if we look this then on a graph, you will see that all the beetles here, these are the term angle of the individual beetles. They will all, apart from a few, that is always the case, turn by 180 degrees using the sun. We can now repeat exactly the same experiment at night, reflecting the moon. And then nothing happens. They will just roll past us, because they are using the polarization pattern over the moon itself. So you can also find these adaptations to what you should be using in the strategy, what you would like to most weight on. It's very flexible because if I wake up one of the nocturnal guys doing the day and we have ways to make them all doing the day. They will actually switch to using the sun rather than the polarization. It's a highly dynamic system. And that, of course, is driven by the brain. The brain of the beetle is obviously bound in its head, and we can take it out. When we started working with them, we thought they were excellent because they would have a huge brain, but I would say like 50% of the stuff in their head is air. So they look at a massive brain being such a big insect. But this is a big brain, and like other brain, it's both different area that serves different purposes. The central complex has been mentioned here already with the ants. And that is found here in the center of the brain, and that is where we find the compass of animals. There are now lots of work going on in reconstructing the network behind orientation in the central complex. This is one of the input neurons. And the way we understand that they are involved in navigation is that we can put an electrode in them and just look at their activity, like was shown also in the former talk. And I just think this demonstrates quite well what is going on in the head of these animals. So here is that in the light source, you can think about it like the mule that the beetles can use, but they prefer not to. And then we will rotate it, and you will see the activity of the mule. So it reacts a lot at the right side of this animal, and then it quiets down again. And you will see the same thing now when we go back into the same direction again. So just by having these neurons that are sensitive to different, to where the moon is at the detail rotate and get out of force, different neurons will fire, and then it needs to stare back to the same firing pattern as before. So what about the nights when there is no moon, because it's actually so that every second night hour is lived without the moon. And then there is no polarization pattern from the moon. There were only stars left, and this is from one of our field sites in South Africa. That is one of the really dark places in the world where you have a beautiful starry sky. So can the beetles use the star story at the time? They were thought about as being too small and their visual system of insects couldn't actually resolve them properly so they could use them. But birds are well known to use stars. They learn the rotational center of the sky that is north. That's how they navigate using stars. Seals can use bright stars to steer their way. But what about the dumb beetles? Well, we can put them on boards like this, which we often do in the field control the substrate. And these here is a track made of this is one vehicle for track. And as you see, they're all very stressed. They have the moon, they have the polarization pattern doing all well. Then we can test the same thing under a starry sky and see what happens. Pretty worse, but most of them are actually doing a very good job. So how lost can the dumb beetles be then? Maybe they can do this just by feeling so to say by their own body movements. Well, to test that, we put a little hat on the beetles. We stopped them from seeing everything in the sky. We can do this during the day or during the night. It doesn't matter the result is the same. This board is only 60 centimeters across. Well, we have put a cap on it so they can wear a transparent cap. They will all find that. But when they can't see the sky, their compass is totally not working anymore. So vehicles can be really lost if you don't give them visual input of the right kind. The vehicles orienting under the stars were long from being this lost. So they were definitely orienting. And it turns out that if you look at the view from the ground, here you see the Milky Way stretching from south to north. We can filter this image to see what it looks like for the beetles. They don't see individual stars. They don't have the resolution for that, but they see the Milky Way. And this is the cue that these animals are using to guide their way through the nights when there is no blue. And with that, we have navigated from land to the stars. And I have to confess that when I started working with Mike Land and all the other wonderful co-authors of this paper, I was a master student. I had no clue how wonderfully famous and good these researchers were. And maybe that was good at the time because I could just truly enjoy the ride. And I'm so happy they pushed me into the direction on navigation in the dark. Thank you. I'm excited with the data. Thanks a lot. But there are many questions. Thanks a lot. So how do they do it when it's overcast? Yeah, so when it's overcast, so the polarization pattern is going to penetrate in the clouds. We have once over 20 years in South Africa, it has been so overcast that they started rolling in circles. But I have looked into this by taking the beetles to moon. And they start rolling in circles. They can't read the magnetic field as far as we understand that would be when to do that. But they can use wind. So in the recent years, now understand that they also have a wind compass. So if it's windy, they will use that to orient by. So it's not really active when it's overcast because it's usually cold as well. Hello. I think that was really well. It was also very interesting to see the finals. Then we got a game where they were followed by the moon. We tried in lines and trying to combine actually navigating the signals. And then in the navigation fields and then in the celebrations. And then we found that the clouds are not interested. So it means they can do it, but they do not want to do it. So despite this never ever. Oh, no, so, so we despite us, we were never able to use the polarizing filter. And we see that if we have a very, very strong light and strongly polarized, they will be attracted to the vector direction. But we can also measure. So from the new one you saw there, it can either be to read or slide in gym intensities, whereas in strong intensities, it's not actually the position of the sun. So we really see this up and down regulation and much weight, they put on it. And what is interesting that, you know, this is what I showed you when we put down the filter has only worked in one species. The other ones, we need to have this filter there already and they roll, you know, we put them under the filter, then they will also respond. So it's a diss in a something that is, it's, it's hard for them to cope with what they suddenly get. Yeah. Yeah, I would love if an individual be okay program in the direction you could make my life so easy, but they, they pick the direction when they have made a new ball. So they will change. It seems totally random. We see no pattern, new ball, new bearing, they just want to get away. Oh yes, we have, yeah, with that is what we and we find that that the eye is smooth, because the lens at the corner, it is very long so it needs to get the focal point below that. And the question is really why, why the long basis. So we, we want to look at this through the lovely lens. And now to see why they have a best of so much in that. So that is really what we want to do. It's flat, because it has the same curvature as the whole eye, it's the flat as it can be. So the question is rather why you make it so so long. Yeah, we create a lot of conflicts in that way and, and what you saw here when we just hold the mirror in the field. It's really causing a conflict between polarized light and the mirror, because they will constantly I mean the polarized light is untouched by my manipulation. So that is why it means that the day activity tools, at least these species that I showed you here are going to prioritize the thumb of the polarized light, but at night, they put higher weight of the polarization pattern that stretches over the sky and they can integrate a lot of life form. So conflicts tell us we do conflicts between sun and wind and all sorts of things, because it's so telling for how these systems work. But we're really much the key and even in South Africa to get a cloud from the sun. Oh, yes, yes, so they can use the polarization pattern, but they put the weight on the sun. The minute is that they don't flinch if you take away the sun. Then they turn over to the polarization pattern. It's not an ordinary thing. I think they will use the wind intensity gradient color gradient is like five, six views at the same time. Yes, that is just a very safest way of doing it so that the view it is, you can have the sun can disappear and won't be affected. Yeah, and they will learn the new relationship to each other by making a dance top of their dongles that's kind of established their relationships. We're going to have to have lunch. Yeah, that was a CLC one year on depending on what animal you work in. So it's an input to the center. I guess they need anywhere to go on.