Transcript

How animals find home

Jochen Zeil

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Matt Smith:

Welcome to the La Trobe University Podcast with myself, Matt Smith. And joining me today is Professor Jochen Zeil. He is a professor from the Research School of Biology at the Australian National University. Thank you for joining me, Jochen.

Jochen Zeil:

Thanks for being here.

Matt Smith:

Professor of ecological neuroscience, can you tell me what is ecological neuroscience? It sounds like it's trying to signify that ecology has a functioning brain of some sort.

Jochen Zeil:

The fundamental issue we need to understand is how animals function in terms of information processing under natural conditions because the challenge is to understand the evolution of brains in the light of ecologically and evolutionarily relevant conditions. And the problem there is that the traditional way of understanding how neurons work, how brains work, is under laboratory conditions with animals that are taken out of their natural context, with neural tissue taken out of the context of the body.

That is the only way we can understand the physiology working of nerve cells. However, they have evolved their computational power under conditions in which animals operate today. So, there needs to be an attempt made to understand the information processing problems animals encounter in their everyday life under these natural conditions. And that's what ecological neuroscience tries to do.

Matt Smith:

The way that you work with it is an animal will not function how it is supposed to normally unless it's in its natural context and environment. That sounds like it's a very hands-on and natural way of researching.

Jochen Zeil:

Yes. When you take an animal into the laboratory, you can always measure something. You can measure how its neurons work and how its sensory systems work. But you never know whether what you can reproduce in the laboratory is actually the natural situation under which these systems function. We need to understand the signal stream as it were or the information processing problems of animals in these real-life conditions. So, yes, we work as much as possible with animals in their natural setting.

Matt Smith:

Part of the research that you've been doing is on how animals find their way home, which I assume by design you can't do if you take the animal out of their natural setting. So, can you tell me about that research and how animal brains function? What have you been finding out there?

Jochen Zeil:

It's little recognized the competence of animals with the world in how they are able to move between places of significance to them with nests or places where they can find food or mates or nest material. It's fundamental to life on Earth. If animals weren't so competent in moving about the world and finding back to places, the world would look very, very different.

I'm working mainly with insects. And the people working with me like Ajay Narendra work in particular with ants. And there we try to understand how individually foraging ants find every day regularly back to their home tree, as it were, where they go foraging. They come out of the ground and then head directly towards these trees. And the most challenging aspect of that is some of the ants we are working with actually navigate at night. So, the question is, how are they are able to find back to places where they collect food every night, again, to the same tree at light levels where we would be unable to do these.

Matt Smith:

Do ants have particularly good eyesight? Can they navigate by the moon or the sun? Or, I suppose, another way that an ant would navigate is by the scent laid down by previous ants and they can navigate by smell?

Jochen Zeil:

These particular ants we're looking at, these are the Australian bulldog ants. They are individual foragers. They don't lay a fair amount of trails. So, each individual animal makes its own navigational decisions. And we know that the night-active ants have actually have evolved night vision equipment or the equivalent of it by having their eyesight improved tremendously in terms of light sensitivity.

For navigation, you need a compass, a sense of direction. And insects are known, and we know from ants that they use basically two kinds of compass-like bits of information. And one is, they use the pattern of polarized skylight at dusk that gives them a sense of direction. But in addition, they use the landmark panorama to guide them. And these are the trees seen against the still bright night sky. And because they have so sensitive eyes, they can actually use these trees as beacons. We can show that they do both by either manipulating what they see of the polarized skylight and by manipulating what they see of the landmark panorama. And through that, we can show that they both, these cues in order to navigate.

Matt Smith:

And so, if an ant navigates to a tree, if an ant knows, "OK, that tree there on horizon, I need to go to that and then turn left," if you take the ant out of its context from where it was there, will it recognize the same tree? I'm sure you've tried that. What sort of reaction do you get from the ant? Do you get a very lost ant or do you get an ant that goes, "OK, I know that tree is the same tree as before"?

Jochen Zeil:

That's a very informed question you've just asked me because this placing an ant as it walks along a track towards a goal is an extremely powerful tool to understand what navigational information the animal uses. You take an ant and you then for instance displace it sideways a few meters from the track it is known to take. And then, three things can happen.

The first thing that can happen is that the animal is completely disoriented. And what the animals then do is they go into a search loop pattern. They basically search around the area.

The second thing that can happen that the animals continue along the direction they were used to walk. And that indicates that they have a compass and that they use a method of navigation that is called path integration. Path integration is a very old method of navigation that basically means that the animals record all their movements and their turns on an outward trip and constantly calculate what's called a home vector that direct route home. And in this case, displacing an animal as it walks out towards a tree path integration would give a direction and a length of a vector, how long the animal would need to walk. And so, if you displace an animal that only path integrates, it disregards the displacement because all the navigation instruction it has are on board and only take account of own active movements. It would simply continue in the same direction.

And the third thing that can happen is that the animal actually compensates for the displacement and changes its direction of travel to continue to head towards the goal tree, for instance. And what we find in most cases if we displace the animals within a certain area around the known track, after looking around a bit, they immediately compensate for the displacement. And what that means is that they navigate by landmarks, which they can recognize even after the displacement has taken place. The interesting bit is when you take the animal very far out of its normal foraging range, then they display path integration information.

So, what these experiments show is that the animals have a whole toolkit of navigational information. And they use any part of it, depending on what the most salient or robust cue is at the moment.

Matt Smith:

Have you found that's the method of navigation for any other animals? That's about bulldog ants, isn't it? Is that sort of thing for other animals, say, Australian ants in general, or is it unique only to bulldog ants?

Jochen Zeil:

Fundamentally, the process of path integration is a very, very old way of navigating. We find that in flying animals, in flying insects, in walking insects, but also in mammals, in vertebrates. They use this always as a backup system. We know also that depending on the world the animals live in, now coming back to ants, they rely either more on path integration process and that is when, for instance, they live in featureless environments like deserts here in Australia but also in Africa. When there are no landmark information available, this process is the only one that they can rely on to return back to their nests, for instance.

But as you study animals that live in more cluttered environments, landmark-rich environments, very often, landmark guidance overrides this underlying path integration process. And so, animals are extremely flexible, even if you have an animal that lives normally in the featureless desert, if you study it in a landmark-rich environment where they also live, or if you give them landmarks, artificial ones, then they will use them. Equally, an animal that normally relies on landmark information, if you take it out of its normal landmark environment, it shows you that underlying it constantly also does this path integration process.

So, this flexibility of navigational information animals use is surprising. And it shows a richness of information processing capacity that is a huge challenge actually for our attempts to build competent robots because these animals have a CPU or central processing unit of about a cubic millimetre of wetwear and yet, with that small brain, they are also competent. It's a huge challenge for us to understand how that can be.

Matt Smith:

I know that they've done experiments before with turtles and how their internal compass works with migration. If they'll reverse the polarity around the turtle, the turtle will start heading in the wrong direction because its compass will be thrown off whack.

Jochen Zeil:

In turtles and in some other animals like lobsters, it is known that they have a magnetic compass, that is true. And in turtles in particular, that's the big challenge over large distances. They also appear to derive global positioning information from the signature of the magnetic field and at different places that are hundreds of kilometres apart.

Matt Smith:

So, a turtle has a sat nav then?

Jochen Zeil:

A sense, yeah.

Matt Smith:

What you take from ants would be very particular to only a few species of ants. But as you've said, between that, you've got turtles and lobsters, two completely different animals, that use the same sort of navigation. Have you been able to find that the ants' method of navigation is also particular with other animals?

Jochen Zeil:

There are only a handful of navigational pieces of information that can be used in principle. And so, there is a very general structure to navigational competence, irrespective of what animal you're looking at. However, there are issues of scale. Some animals like birds move on a continental scale, some over global dimensions. And we only know about these since a few decades of being able to track these animals over these large distances with satellite equipment and so on and so on.

The big difference, I think, on that global scale is to understand what global signatures there are that allow animals to know where they are, not only where they are going. But the big surprise is to see that these globally migrating animals also know something about where they are on the globe. And so far, the only general kind of information that appears to be available to them is the structure of the magnetic field and how it changes on a global scale.

When you track, for instance, storks that regularly fly to Africa from Europe on these migration routes, then you can also see that the animals take note of landscape features, like they travel along coastlines, for instance. They don't like to travel across open water; they minimize that. Some birds have been shown to fly along rivers and then wait for a bridge to come. And then, they fly across the river, over the bridge and then turn along the river again. They don't like to fly over water, for instance. Other big features like mountain ranges and so on do seem to guide animals on that scale.

There are also big insect migrations across the Alps, for instance, in Europe. And there, it seems that these animals come with an instruction of in which direction to fly for how long or how far. In birds, at least, it has been shown how that instruction is unravelled. It's that they fly, depending on the fuel they have accumulated. So, they burn fuel and that burning of fuel is their odometer, as it were.

And so, yes, animals can come with genetic instructions about how to move across the world. But on a local scale, finding a nest or finding back to a food tree, this is not something that can be genetically instructed, that needs to be learned every time again, especially in animals where the environment can change radically, for instance, by big-footed animals or by storms or by falling logs or whatever, that can disturb a small-scale environment of a small insect with a nest that is only about a couple of millimetres across.

So, there are bits that need to be learned. And then, there are certain phenomena of animal movements that seem to come with genetic instructions.

Matt Smith:

That's all the time we've got for the La Trobe University Podcast today. If you have any questions, comments or feedback for this podcast or any other, you can send us an email at podcast@latrobe.edu.au. Professor Jochen Zeil, thank you for your time today.

Jochen Zeil:

Thanks for having me.