Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences at the University of Oxford,
and we're right in the middle of this very serious corona virus crisis right now.
And my students are all stuck at home and we want to keep them in touch with biology and keep in touch with us.
And so we're going to make a new series of videos and they're going to be called back garden biology.
Hello and welcome to this week's episode of Backgammon Biology. And I just simply need to say I always sweep the leaves off the lawn,
but I hope you can see that the lawn is nevertheless covered in leaves, just hair.
And I know who's responsible for that. It's the blackbirds as I see them here.
I met tossing the leaves off the flower beds so they can see if they can find anything underneath them.
And of course, what they're looking for is the humble earthworm.
And this episode is going to be dedicated to the humble earthworm because they are actually really cool creatures and they're very important.
And gardens, every gardener is familiar with them. And I thought it'd be interesting to explore them a little bit more in the first piece.
What I'm going to do is think about how earthworms move.
And that's a way of also looking generally at the way muscles work because earthworms, you move using their muscles just like any other animal does.
So let's take a look at that first. So let's think about how the worm moves.
Now, the worm is a type of worm called an analyst worm.
And the key feature of analyst worms, as opposed to other kinds of worms, is that their bodies are divided into segments.
And that's really crucial for that movement. Now, within the segments, there are muscles or animals move because of their muscles.
So how do muscles work? Well, muscles are a special type of cell, and inside them there are lots of very thin fibres,
micro fibres, if you like, and they are aligned in particular directions.
So let's imagine my hands going to represent a muscle. So are my fingers here.
All those fibres are now aligned together. And what happens when the muscle cell contracts is that those little tiny fibres slide between each other.
There are actually two kinds of base filaments, sitcom's and thin ones and thick ones can slide between thin ones.
And that's a very active process that uses up a lot of energy for the cell.
And you can see the effect in my films represent either side of the muscle cell.
Is that it will shorten and contract my thumbs, move closer together and inside a muscle.
All of the cells are aligned in the same way. So they're all pulling together.
So when they all contract, the muscle cells become shorter. All right.
Let's see that in action. I've got a muscle in here. It's called a bicep. And optically it's not a huge muscle or anything.
But if I contract it and shorten the muscle, it's attached to this bone here.
So it will lift this lower part of my arm up. Now, the problem with the muscle cells actually is they can't move back again.
So they can use up energy. They can slide together like that, but then they'll actually be stuck.
So how are they going to move back to their original position when he's going to pull them back?
Well, in this case, my arm it's this muscle here. It's now stretched out when this one contracted.
Now it's going to contract and that contraction stretches.
This muscle lines again. So in our bodies, we have the muscles working and antagonistic pairs producing the opposite movement.
And that's because otherwise, every time you move to be stuck there. Now, how is that going to work with the worm's body?
A body isn't doesn't consist of a series of levers like my body does.
It's a thin cylinder. But as we said, devised segments.
Let's watch a worm move things. I capture this worm, put it in this nice, clean flowerpot saucer.
I filmed that as it was wandering around.
And you can see it can extend its head by stretching out some of those segments and making them long and thin while other segments
remain short and fat and anchor the wound to the ground and then it pulls up the bottom half of its body as it happens forward.
So it's really essential to its movement that it can make some segments long and thin and some segments short and fat.
How is it going to do that? Well, here's my paper representation of a worm segment.
So just move those to one side. I've got long, thin segments. I've got short fat ones.
And how can muscles achieve that? Well, let's begin by looking at what are called the circular muscle.
So in every segment, there are muscles that go around the segments and as they contract,
they will squeeze down on the segments and make it into a long, thin segment.
And it would get stuck there unless the worm has another set of muscles in the body wall and they go from top to bottom of the segments.
And when they contract a squeeze down on the segment, they turnitin to a short fat segment.
So these these muscles, again, just like in our body, they work in antagonism.
It's got the circular muscles and it's got the longer chewed and all muscles working in opposition to make the segments long and thin or shorten fat.
I mean, it obviously needs nerves to coordinate that movement so that some of the segments will be longer then and others will be short.
I really recommend going out, finding out where, putting in just not that and watching it.
It's actually quite fascinating. And you'll also see that it does have a head end with some sense organs on it.
It prefers to lead with the head, but it can actually lead. But the rear end of it won't stand if it needs to.
It can make it go the other direction and you can to save time, little bristles on the body.
So when the seconds become salt and fat, there's bristles push in to the soil and anchor.
So quite a nice thing to watch. Okay, so we found out a little bit that about earthworms,
that they're segmented their bodies and that they can move nicely using their coordinated muscle action.
And I hope you enjoy looking at how somebody in our department really knows a lot about earthworms and other kinds of worms.
And his name is Professor Peter Holland, and he teaches our first shares a lot about different kinds of animal groups.
And I thought be interesting to ask Peter about Charles Darwin and his relationship
to Essence because Charles Darwin wrote a whole book about earthworms.
So I got hold of Peter and agreed to have the same conversation with him.
And I began by asking him just why did Darwin find earthworms so fascinating?
Darwin was really fascinated by earthworms in a sort of orthodoxy. When you look back at what Darwin wrote.
He did the work on earthworms just seemed to be something he kept dipping back to through his life.
But one of the first scientific papers he published when he came back from the Beagle voyage was on earthworms.
And it was just a short note to the geological society.
And then 40 more than 40 years later, he wrote his large book on earthworms, which was the last book he wrote before he died.
So it came out to 1881, just six months before he died.
And in fact, I think he was getting pretty fed up with earthworms by that stage, having worked on them for more than 40 years,
because he even though there's a really nice letter that he wrote to someone saying these,
he really wants to finish this book on earthworms before joining them.
So I thought that was quite nice. But anyway, so why why did they fascinate him so much?
Well, I think actually it is because he was dealing with fascinated by change, shape, change on the planet.
And of course, we think about that in terms of natural selection and evolution and quite long term periods of change.
But he was really interested in anything which was changing on the planet, erosion as well.
Geologic processes. And what we think by earthworms,
what he was able to show and what he had learnt really was the earthworms are changing the planet over quite short time periods by moving soil,
burying things.
And he was really impressed by how he could see even buildings disappear, old buildings being covered by soil, which he put down to earthworms.
So I think he was fascinated because they were agents of change. Oh, that's really cool.
I'd never thought of it like that at all. And he managed to sell an entire book about accents.
Well, let's not forget, he'd been looking at them for 40 years. He had he had 40 years of meticulous.
His own meticulous observations on them and lots of experiments he did on them.
So he wrote about their behaviour, like how worms move in Burrows.
He wrote about their ecology, what they feed on and how they passed soil through their guts.
He wrote loads in the book about effects on humans. I mentioned buildings, but he wrote about how soils were turned over.
The soil was so important for farming and for plant growth because it created aeration of the soil and helped drainage and it move nutrients around.
He wrote a lot about that. So he had all that material that he had gathered and not just by his own research,
but also writing to people in correspondence and reading all the literature beforehand that had come about worms.
And some of his experiments were really quite fascinating, actually.
He now, though, there is he describes him in the book, how he bring worms into the house,
and then he'd play the piano to them or somebody in the family would play the piano and see if they would respond.
And then he they had a bassoon. He'd play the bassoon at them, see if they'd respond to different notes,
shine shining a candle near them to see if they responded to light or even that.
What one passage where he takes out a red hot poker and he doesn't touch the worm with it,
but he brings it near the worm to see if he can feel that heat nearby, says all those sorts of experiments that he did.
So he really did have a have a lot of information to packet of package with book.
God, I feel sorry for those where obviously it sounds like bit like a sort of weather nightmare then going into Darwin's house.
So what do you think is most fascinating discovery was or perhaps what was his most important discovery about Wens?
Well, I think his discoveries about their sense organs were quite important because people hadn't thought about that very much before.
So, you know, those experiments I just mentioned showed that earthworms can detect vibrations,
but they weren't able to detect airborne sounds, for instance. So those were interesting.
But probably the most important were were his discoveries on how much soil passed through
the guts of earthworms and what effect that had on the whole structure of the soil.
And of course, he wasn't the first person to point out that soil was being moved around by earthworms in Gilbert White.
That wrote about that in the seventeen hundreds. But Darwin was actually quite quantitative.
So he tried to calculate with experiments and observations how much soil was moving.
So for instance, he even in his garden, he built something which he called his worms stone,
which was a great big round stone, like a millstone, really a little bit smaller with a hole in the middle.
And this is a flat stone he put on the ground. And he wanted to measure how long it would take for it to be to sink into the earth because
earthworms were sort of moved eating soil and then passing it up into worm casts onto the ground.
So to measure it, he inserted a sort of measuring rod down the sand, which went down further into the ground.
We didn't move. And then you could sort of measure as the worm stone dropped.
And he he he he thought that the earth was probably being turned over at a rate of about five centimetres per year per year,
or that at a maximum, it may have been a bit less, may have been some one centimetre a year.
We would have buried in different places anyway.
But I think the important thing is he realised just how mean massively important that is for plant growth,
moving nutrients around, aerating the soil, making channels and actually moving everything around.
So, yeah, I think those were the most fascinating discoveries. Right.
So what didn't he know? What do we know now about worms that were just dormant?
If we could bring it back down, telling these things that obviously I'm sure he'd be delighted to find out what we
know about atoms now that he didn't know anything special that you would point to.
Yeah, I think a couple of things. One is diversity of different earthworm species.
So we have 27 species of earthworms in the UK and there's probably more than a thousand, maybe 5000 species around the world.
And they're they re colleges are on their behaviours are a little bit different from each other.
And he didn't really write very much about that in the book. He sort of group them all together.
But of course, we now know that some will make vertical burrows, which they'll pull leaves down into others,
which was that he was most fascinated in are the ones making horizontal burrows and eating
soil and others just live in leaf litter says quite a lot of ecological diversity.
And I don't think he realised that.
But also the some of the more recent works, it shows the earthworms are quite tolerant of heavy metals in the in the soil,
things like cadmium, copper, gold concentrations that will kill a lot of other invertebrates.
Earthworms seem to get to tolerate them. And we know that they've got particular proteins, Battalia findings which combined,
and sequester those metals to stop them having a harmful effect on the animals.
So they they do have these really interesting biochemical adaptations to toxic chemicals in the soil.
So I think, yeah, we would have found that fascinating, I'm sure, because there's a bit of natural selection must have led to that.
Okay, so peace pieces, obviously a farm.
And he can explain why Darwin was so fascinated with webs and what he knew about them and what he'd probably like to know about them.
And what are the other things that I find really fascinating about worms? Is this actually a massive abundance of them in this garden?
And every time I dig, I find them. So they're really, really important for lots of other organisms that live in the garden, like the blackbirds.
And you can watch the blackbirds running over the lawn and you can see them put the head to one side and
are listening for worms and other things that are moving under the soil so they can rush in and grab them.
And foxes, for example, often come through gardens. They can actually eat quite a lot of earthworms and so can batches.
Of course, batches eat enormous quantities of earthworms. I don't have patches in my garden.
One of my students has been finding them in his garden and put a camera trap.
So some of that footage. Thanks very much, Tamraz. I'm going to include here. Very good timing, Matt.
And in America as well, there are lots of different types of ants. And there's a guy there studying them.
And he noticed or he found out that some people in the states,
they put a big iron stake into the soil and then they run a sort of file over the top of it to create these deep vibrations.
And when they do that, all these worms come up to the surface and they collect them and they sell them for fishing bait.
And you can. She make a living amazingly, but he wanted to know what was the adaptive value of that?
Why would earthworms come pouring out of the soil? When you play this tune to them?
And his hypothesis was that this was actually something to do as an anti predator behaviour.
And he knows that moles. Right. Moles are massive hunters of earthworms and not just foxes, not just badgers, but moles.
Pretty much only eat worms. And that perhaps this vibration was then was mimicking the sound of a mole coming through a tunnel and digging.
And the best escape for the worms, if they hear a mole coming, is to get above ground.
Moles never come above ground. And so he did this amazing, cool experiment.
I've got a little video of it here to show you why he had a box. He filled it with worms.
And you can see on the surface, it's no worms at all. And he introduces a mole.
And sure enough, all the worms come pouring out as they hear the mole approaching.
And that's a really nice paper that's published in what's called Open Access Journal,
where anybody is allowed to go and access that paper and use the footage.
So thank you very much to him for doing that great piece of work. Okay.
Well, that's it for background biology this week. I hope you can enjoy finding some worms in your garden if it goes very cold.
Of course, you don't find them so easily. They're not very active. If it goes cold, may go down deeper into the soil.
But if you get a trial, I'm sure you can find or move the plant possibly, too.
And certainly as the weather gets warmer, they'll start getting a lot more active. So take care.