1 00:00:00,300 --> 00:00:07,460 Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences at the University of Oxford, 2 00:00:07,460 --> 00:00:11,490 and we're right in the middle of this very serious corona virus crisis right now. 3 00:00:11,490 --> 00:00:17,150 And my students are all stuck at home and we want to keep them in touch with biology and keep in touch with us. 4 00:00:17,150 --> 00:00:46,110 And so we're going to make a new series of videos and they're going to be called back garden biology. 5 00:00:46,110 --> 00:00:53,450 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, 6 00:00:53,450 --> 00:00:57,150 but I hope you can see that the lawn is nevertheless covered in leaves, just hair. 7 00:00:57,150 --> 00:01:01,290 And I know who's responsible for that. It's the blackbirds as I see them here. 8 00:01:01,290 --> 00:01:06,420 I met tossing the leaves off the flower beds so they can see if they can find anything underneath them. 9 00:01:06,420 --> 00:01:09,700 And of course, what they're looking for is the humble earthworm. 10 00:01:09,700 --> 00:01:16,620 And this episode is going to be dedicated to the humble earthworm because they are actually really cool creatures and they're very important. 11 00:01:16,620 --> 00:01:24,630 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. 12 00:01:24,630 --> 00:01:28,190 What I'm going to do is think about how earthworms move. 13 00:01:28,190 --> 00:01:36,600 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. 14 00:01:36,600 --> 00:01:41,880 So let's take a look at that first. So let's think about how the worm moves. 15 00:01:41,880 --> 00:01:45,270 Now, the worm is a type of worm called an analyst worm. 16 00:01:45,270 --> 00:01:51,240 And the key feature of analyst worms, as opposed to other kinds of worms, is that their bodies are divided into segments. 17 00:01:51,240 --> 00:01:58,740 And that's really crucial for that movement. Now, within the segments, there are muscles or animals move because of their muscles. 18 00:01:58,740 --> 00:02:08,160 So how do muscles work? Well, muscles are a special type of cell, and inside them there are lots of very thin fibres, 19 00:02:08,160 --> 00:02:12,430 micro fibres, if you like, and they are aligned in particular directions. 20 00:02:12,430 --> 00:02:16,660 So let's imagine my hands going to represent a muscle. So are my fingers here. 21 00:02:16,660 --> 00:02:27,030 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. 22 00:02:27,030 --> 00:02:33,660 There are actually two kinds of base filaments, sitcom's and thin ones and thick ones can slide between thin ones. 23 00:02:33,660 --> 00:02:37,620 And that's a very active process that uses up a lot of energy for the cell. 24 00:02:37,620 --> 00:02:41,850 And you can see the effect in my films represent either side of the muscle cell. 25 00:02:41,850 --> 00:02:47,490 Is that it will shorten and contract my thumbs, move closer together and inside a muscle. 26 00:02:47,490 --> 00:02:52,260 All of the cells are aligned in the same way. So they're all pulling together. 27 00:02:52,260 --> 00:02:56,670 So when they all contract, the muscle cells become shorter. All right. 28 00:02:56,670 --> 00:03:02,370 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. 29 00:03:02,370 --> 00:03:07,900 But if I contract it and shorten the muscle, it's attached to this bone here. 30 00:03:07,900 --> 00:03:15,000 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. 31 00:03:15,000 --> 00:03:20,100 So they can use up energy. They can slide together like that, but then they'll actually be stuck. 32 00:03:20,100 --> 00:03:25,720 So how are they going to move back to their original position when he's going to pull them back? 33 00:03:25,720 --> 00:03:31,920 Well, in this case, my arm it's this muscle here. It's now stretched out when this one contracted. 34 00:03:31,920 --> 00:03:35,730 Now it's going to contract and that contraction stretches. 35 00:03:35,730 --> 00:03:42,780 This muscle lines again. So in our bodies, we have the muscles working and antagonistic pairs producing the opposite movement. 36 00:03:42,780 --> 00:03:49,170 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? 37 00:03:49,170 --> 00:03:54,060 A body isn't doesn't consist of a series of levers like my body does. 38 00:03:54,060 --> 00:03:58,300 It's a thin cylinder. But as we said, devised segments. 39 00:03:58,300 --> 00:04:03,690 Let's watch a worm move things. I capture this worm, put it in this nice, clean flowerpot saucer. 40 00:04:03,690 --> 00:04:06,180 I filmed that as it was wandering around. 41 00:04:06,180 --> 00:04:13,740 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 42 00:04:13,740 --> 00:04:20,520 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. 43 00:04:20,520 --> 00:04:27,220 So it's really essential to its movement that it can make some segments long and thin and some segments short and fat. 44 00:04:27,220 --> 00:04:32,240 How is it going to do that? Well, here's my paper representation of a worm segment. 45 00:04:32,240 --> 00:04:36,870 So just move those to one side. I've got long, thin segments. I've got short fat ones. 46 00:04:36,870 --> 00:04:42,240 And how can muscles achieve that? Well, let's begin by looking at what are called the circular muscle. 47 00:04:42,240 --> 00:04:48,150 So in every segment, there are muscles that go around the segments and as they contract, 48 00:04:48,150 --> 00:04:54,930 they will squeeze down on the segments and make it into a long, thin segment. 49 00:04:54,930 --> 00:05:03,540 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. 50 00:05:03,540 --> 00:05:10,830 And when they contract a squeeze down on the segment, they turnitin to a short fat segment. 51 00:05:10,830 --> 00:05:15,300 So these these muscles, again, just like in our body, they work in antagonism. 52 00:05:15,300 --> 00:05:24,780 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. 53 00:05:24,780 --> 00:05:31,950 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. 54 00:05:31,950 --> 00:05:36,230 I really recommend going out, finding out where, putting in just not that and watching it. 55 00:05:36,230 --> 00:05:41,520 It's actually quite fascinating. And you'll also see that it does have a head end with some sense organs on it. 56 00:05:41,520 --> 00:05:47,900 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. 57 00:05:47,900 --> 00:05:53,140 It can make it go the other direction and you can to save time, little bristles on the body. 58 00:05:53,140 --> 00:05:57,940 So when the seconds become salt and fat, there's bristles push in to the soil and anchor. 59 00:05:57,940 --> 00:06:03,940 So quite a nice thing to watch. Okay, so we found out a little bit that about earthworms, 60 00:06:03,940 --> 00:06:10,420 that they're segmented their bodies and that they can move nicely using their coordinated muscle action. 61 00:06:10,420 --> 00:06:17,350 And I hope you enjoy looking at how somebody in our department really knows a lot about earthworms and other kinds of worms. 62 00:06:17,350 --> 00:06:25,210 And his name is Professor Peter Holland, and he teaches our first shares a lot about different kinds of animal groups. 63 00:06:25,210 --> 00:06:29,770 And I thought be interesting to ask Peter about Charles Darwin and his relationship 64 00:06:29,770 --> 00:06:34,270 to Essence because Charles Darwin wrote a whole book about earthworms. 65 00:06:34,270 --> 00:06:37,440 So I got hold of Peter and agreed to have the same conversation with him. 66 00:06:37,440 --> 00:06:44,350 And I began by asking him just why did Darwin find earthworms so fascinating? 67 00:06:44,350 --> 00:06:50,310 Darwin was really fascinated by earthworms in a sort of orthodoxy. When you look back at what Darwin wrote. 68 00:06:50,310 --> 00:06:55,690 He did the work on earthworms just seemed to be something he kept dipping back to through his life. 69 00:06:55,690 --> 00:07:02,410 But one of the first scientific papers he published when he came back from the Beagle voyage was on earthworms. 70 00:07:02,410 --> 00:07:05,970 And it was just a short note to the geological society. 71 00:07:05,970 --> 00:07:14,260 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. 72 00:07:14,260 --> 00:07:17,540 So it came out to 1881, just six months before he died. 73 00:07:17,540 --> 00:07:23,580 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, 74 00:07:23,580 --> 00:07:27,940 because he even though there's a really nice letter that he wrote to someone saying these, 75 00:07:27,940 --> 00:07:31,630 he really wants to finish this book on earthworms before joining them. 76 00:07:31,630 --> 00:07:38,410 So I thought that was quite nice. But anyway, so why why did they fascinate him so much? 77 00:07:38,410 --> 00:07:45,730 Well, I think actually it is because he was dealing with fascinated by change, shape, change on the planet. 78 00:07:45,730 --> 00:07:51,820 And of course, we think about that in terms of natural selection and evolution and quite long term periods of change. 79 00:07:51,820 --> 00:07:58,960 But he was really interested in anything which was changing on the planet, erosion as well. 80 00:07:58,960 --> 00:08:02,440 Geologic processes. And what we think by earthworms, 81 00:08:02,440 --> 00:08:11,200 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, 82 00:08:11,200 --> 00:08:12,430 burying things. 83 00:08:12,430 --> 00:08:20,950 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. 84 00:08:20,950 --> 00:08:25,930 So I think he was fascinated because they were agents of change. Oh, that's really cool. 85 00:08:25,930 --> 00:08:32,710 I'd never thought of it like that at all. And he managed to sell an entire book about accents. 86 00:08:32,710 --> 00:08:38,210 Well, let's not forget, he'd been looking at them for 40 years. He had he had 40 years of meticulous. 87 00:08:38,210 --> 00:08:44,710 His own meticulous observations on them and lots of experiments he did on them. 88 00:08:44,710 --> 00:08:49,960 So he wrote about their behaviour, like how worms move in Burrows. 89 00:08:49,960 --> 00:08:56,020 He wrote about their ecology, what they feed on and how they passed soil through their guts. 90 00:08:56,020 --> 00:09:04,090 He wrote loads in the book about effects on humans. I mentioned buildings, but he wrote about how soils were turned over. 91 00:09:04,090 --> 00:09:16,150 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. 92 00:09:16,150 --> 00:09:22,540 He wrote a lot about that. So he had all that material that he had gathered and not just by his own research, 93 00:09:22,540 --> 00:09:30,730 but also writing to people in correspondence and reading all the literature beforehand that had come about worms. 94 00:09:30,730 --> 00:09:33,970 And some of his experiments were really quite fascinating, actually. 95 00:09:33,970 --> 00:09:39,460 He now, though, there is he describes him in the book, how he bring worms into the house, 96 00:09:39,460 --> 00:09:45,430 and then he'd play the piano to them or somebody in the family would play the piano and see if they would respond. 97 00:09:45,430 --> 00:09:53,320 And then he they had a bassoon. He'd play the bassoon at them, see if they'd respond to different notes, 98 00:09:53,320 --> 00:09:59,010 shine shining a candle near them to see if they responded to light or even that. 99 00:09:59,010 --> 00:10:03,720 What one passage where he takes out a red hot poker and he doesn't touch the worm with it, 100 00:10:03,720 --> 00:10:10,600 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. 101 00:10:10,600 --> 00:10:15,550 So he really did have a have a lot of information to packet of package with book. 102 00:10:15,550 --> 00:10:22,300 God, I feel sorry for those where obviously it sounds like bit like a sort of weather nightmare then going into Darwin's house. 103 00:10:22,300 --> 00:10:30,880 So what do you think is most fascinating discovery was or perhaps what was his most important discovery about Wens? 104 00:10:30,880 --> 00:10:38,740 Well, I think his discoveries about their sense organs were quite important because people hadn't thought about that very much before. 105 00:10:38,740 --> 00:10:44,710 So, you know, those experiments I just mentioned showed that earthworms can detect vibrations, 106 00:10:44,710 --> 00:10:50,200 but they weren't able to detect airborne sounds, for instance. So those were interesting. 107 00:10:50,200 --> 00:10:57,940 But probably the most important were were his discoveries on how much soil passed through 108 00:10:57,940 --> 00:11:03,360 the guts of earthworms and what effect that had on the whole structure of the soil. 109 00:11:03,360 --> 00:11:09,970 And of course, he wasn't the first person to point out that soil was being moved around by earthworms in Gilbert White. 110 00:11:09,970 --> 00:11:15,250 That wrote about that in the seventeen hundreds. But Darwin was actually quite quantitative. 111 00:11:15,250 --> 00:11:21,160 So he tried to calculate with experiments and observations how much soil was moving. 112 00:11:21,160 --> 00:11:26,310 So for instance, he even in his garden, he built something which he called his worms stone, 113 00:11:26,310 --> 00:11:33,910 which was a great big round stone, like a millstone, really a little bit smaller with a hole in the middle. 114 00:11:33,910 --> 00:11:41,080 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 115 00:11:41,080 --> 00:11:48,640 earthworms were sort of moved eating soil and then passing it up into worm casts onto the ground. 116 00:11:48,640 --> 00:11:53,950 So to measure it, he inserted a sort of measuring rod down the sand, which went down further into the ground. 117 00:11:53,950 --> 00:11:58,660 We didn't move. And then you could sort of measure as the worm stone dropped. 118 00:11:58,660 --> 00:12:08,310 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, 119 00:12:08,310 --> 00:12:16,140 or that at a maximum, it may have been a bit less, may have been some one centimetre a year. 120 00:12:16,140 --> 00:12:18,460 We would have buried in different places anyway. 121 00:12:18,460 --> 00:12:24,160 But I think the important thing is he realised just how mean massively important that is for plant growth, 122 00:12:24,160 --> 00:12:31,420 moving nutrients around, aerating the soil, making channels and actually moving everything around. 123 00:12:31,420 --> 00:12:35,440 So, yeah, I think those were the most fascinating discoveries. Right. 124 00:12:35,440 --> 00:12:39,900 So what didn't he know? What do we know now about worms that were just dormant? 125 00:12:39,900 --> 00:12:44,770 If we could bring it back down, telling these things that obviously I'm sure he'd be delighted to find out what we 126 00:12:44,770 --> 00:12:49,940 know about atoms now that he didn't know anything special that you would point to. 127 00:12:49,940 --> 00:12:53,590 Yeah, I think a couple of things. One is diversity of different earthworm species. 128 00:12:53,590 --> 00:13:02,140 So we have 27 species of earthworms in the UK and there's probably more than a thousand, maybe 5000 species around the world. 129 00:13:02,140 --> 00:13:06,190 And they're they re colleges are on their behaviours are a little bit different from each other. 130 00:13:06,190 --> 00:13:11,320 And he didn't really write very much about that in the book. He sort of group them all together. 131 00:13:11,320 --> 00:13:16,870 But of course, we now know that some will make vertical burrows, which they'll pull leaves down into others, 132 00:13:16,870 --> 00:13:21,700 which was that he was most fascinated in are the ones making horizontal burrows and eating 133 00:13:21,700 --> 00:13:25,990 soil and others just live in leaf litter says quite a lot of ecological diversity. 134 00:13:25,990 --> 00:13:28,300 And I don't think he realised that. 135 00:13:28,300 --> 00:13:36,250 But also the some of the more recent works, it shows the earthworms are quite tolerant of heavy metals in the in the soil, 136 00:13:36,250 --> 00:13:44,110 things like cadmium, copper, gold concentrations that will kill a lot of other invertebrates. 137 00:13:44,110 --> 00:13:52,480 Earthworms seem to get to tolerate them. And we know that they've got particular proteins, Battalia findings which combined, 138 00:13:52,480 --> 00:13:56,800 and sequester those metals to stop them having a harmful effect on the animals. 139 00:13:56,800 --> 00:14:03,640 So they they do have these really interesting biochemical adaptations to toxic chemicals in the soil. 140 00:14:03,640 --> 00:14:10,390 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. 141 00:14:10,390 --> 00:14:12,220 Okay, so peace pieces, obviously a farm. 142 00:14:12,220 --> 00:14:19,530 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. 143 00:14:19,530 --> 00:14:25,490 And what are the other things that I find really fascinating about worms? Is this actually a massive abundance of them in this garden? 144 00:14:25,490 --> 00:14:32,020 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. 145 00:14:32,020 --> 00:14:36,110 And you can watch the blackbirds running over the lawn and you can see them put the head to one side and 146 00:14:36,110 --> 00:14:43,420 are listening for worms and other things that are moving under the soil so they can rush in and grab them. 147 00:14:43,420 --> 00:14:50,800 And foxes, for example, often come through gardens. They can actually eat quite a lot of earthworms and so can batches. 148 00:14:50,800 --> 00:14:55,660 Of course, batches eat enormous quantities of earthworms. I don't have patches in my garden. 149 00:14:55,660 --> 00:15:00,300 One of my students has been finding them in his garden and put a camera trap. 150 00:15:00,300 --> 00:15:05,830 So some of that footage. Thanks very much, Tamraz. I'm going to include here. Very good timing, Matt. 151 00:15:05,830 --> 00:15:11,200 And in America as well, there are lots of different types of ants. And there's a guy there studying them. 152 00:15:11,200 --> 00:15:16,090 And he noticed or he found out that some people in the states, 153 00:15:16,090 --> 00:15:24,580 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. 154 00:15:24,580 --> 00:15:30,010 And when they do that, all these worms come up to the surface and they collect them and they sell them for fishing bait. 155 00:15:30,010 --> 00:15:35,400 And you can. She make a living amazingly, but he wanted to know what was the adaptive value of that? 156 00:15:35,400 --> 00:15:40,200 Why would earthworms come pouring out of the soil? When you play this tune to them? 157 00:15:40,200 --> 00:15:45,720 And his hypothesis was that this was actually something to do as an anti predator behaviour. 158 00:15:45,720 --> 00:15:52,380 And he knows that moles. Right. Moles are massive hunters of earthworms and not just foxes, not just badgers, but moles. 159 00:15:52,380 --> 00:16:00,780 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. 160 00:16:00,780 --> 00:16:05,220 And the best escape for the worms, if they hear a mole coming, is to get above ground. 161 00:16:05,220 --> 00:16:09,840 Moles never come above ground. And so he did this amazing, cool experiment. 162 00:16:09,840 --> 00:16:13,920 I've got a little video of it here to show you why he had a box. He filled it with worms. 163 00:16:13,920 --> 00:16:17,820 And you can see on the surface, it's no worms at all. And he introduces a mole. 164 00:16:17,820 --> 00:16:24,000 And sure enough, all the worms come pouring out as they hear the mole approaching. 165 00:16:24,000 --> 00:16:28,260 And that's a really nice paper that's published in what's called Open Access Journal, 166 00:16:28,260 --> 00:16:31,840 where anybody is allowed to go and access that paper and use the footage. 167 00:16:31,840 --> 00:16:35,580 So thank you very much to him for doing that great piece of work. Okay. 168 00:16:35,580 --> 00:16:40,410 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. 169 00:16:40,410 --> 00:16:45,560 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. 170 00:16:45,560 --> 00:16:49,230 But if you get a trial, I'm sure you can find or move the plant possibly, too. 171 00:16:49,230 --> 00:17:17,192 And certainly as the weather gets warmer, they'll start getting a lot more active. So take care.