1 00:00:00,000 --> 00:00:05,000 Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences 2 00:00:05,000 --> 00:00:10,000 at the University of Oxford, and we're right in the middle of this very serious corona virus crisis right 3 00:00:10,000 --> 00:00:15,000 now. And my students are all stuck at home and we want to keep them in touch with biology 4 00:00:15,000 --> 00:00:21,000 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 5 00:00:21,000 --> 00:00:46,000 biology. 6 00:00:46,000 --> 00:00:51,000 Welcome to my first episode. Every episode is going to start with something that I can find in 7 00:00:51,000 --> 00:00:56,000 my garden. The prime minister's just declared that we're all under lockdown. Nobody's 8 00:00:56,000 --> 00:01:01,000 allowed to leave their house. Yes, they absolutely have to. So I'm going to have to be quite creative about the way we 9 00:01:01,000 --> 00:01:06,000 make these videos. Today's episode is going to start with this flower here. This 10 00:01:06,000 --> 00:01:12,000 is the common primrose. This is a native British flower. You can find it all over 11 00:01:12,000 --> 00:01:17,000 the U.K. It's classic habitat is at the bottom of hedges. That's where it really likes to grow. It 12 00:01:17,000 --> 00:01:22,000 doesn't like to be too dry and it doesn't like to be too wet. But it used to be enormously abundant 13 00:01:22,000 --> 00:01:27,000 and there's still lots of them to be found. And in fact, by one of those things that you seem to be seeing more and more of 14 00:01:27,000 --> 00:01:33,000 as people manage the Vergis better by the roads and motorways, they're really making a bit of a comeback. 15 00:01:33,000 --> 00:01:39,000 And if we look again closely at one, what you can see here is this is a classic wild primrose 16 00:01:39,000 --> 00:01:44,000 where each flower is on its own separate stalk and lurking behind it. Here's something 17 00:01:44,000 --> 00:01:49,000 a bit unusual. I don't know how well we can see this by move those on that away. 18 00:01:49,000 --> 00:01:54,000 We have a big, long stalk and a great cluster of flowers on the top. That's 19 00:01:54,000 --> 00:01:59,000 not a classic primrose and it's something to do with hybridisation. So that primroses 20 00:01:59,000 --> 00:02:04,000 as hybridise with some other flower and we can go and take a look at what the possible culprit 21 00:02:04,000 --> 00:02:09,000 is. That's caused that in a moment. So we've come to another part of the garden where growing in a different 22 00:02:09,000 --> 00:02:15,000 part of the lawn, we have another primula species. So the first thing we looked at was the common primrose. 23 00:02:15,000 --> 00:02:21,000 That's Premolar Vulgaris. This is the Cowslip. That's Primula virus. 24 00:02:21,000 --> 00:02:26,000 And you see that it's very different construction. So it has a single long stand and then a whole 25 00:02:26,000 --> 00:02:31,000 bunch of flowers coming off the top, which is a little bit like that, ABBA and Primrose or so. And that's 26 00:02:31,000 --> 00:02:37,000 because that ABBA and Primrose is almost certainly a hybrid between the primrose and the cowslip, 27 00:02:37,000 --> 00:02:42,000 and those hybrids do occur naturally. And it forms something called an ox lip, which is actually quite a rare 28 00:02:42,000 --> 00:02:47,000 thing to find in nature. And it has the structure of the cowslip, but the individual flowers are big 29 00:02:47,000 --> 00:02:52,000 and it has the pale, buttery yellow colour of the primrose. And gardeners 30 00:02:52,000 --> 00:02:57,000 are taking advantage of those things and may have produced hybrids in an incredible 31 00:02:57,000 --> 00:03:03,000 and, frankly, hideous array of colours and size. So if you go to a garden centre, 32 00:03:03,000 --> 00:03:08,000 you can buy things called polymorphous, and they are deliberate hybrids between cowslips 33 00:03:08,000 --> 00:03:14,000 and primroses, which have been bred to have wacky colours, which, well, personally I don't really like. 34 00:03:14,000 --> 00:03:20,000 Okay. So what we've seen is there are two native premolars is common, the primrose and the cowslip. 35 00:03:20,000 --> 00:03:25,000 And the reason they're interesting is because they have a really cool mating system. And that's actually 36 00:03:25,000 --> 00:03:30,000 what I want to talk about, the mating system of the primrose. So before we look at the strange 37 00:03:30,000 --> 00:03:35,000 mating system of the primrose, I thought it'd be good to refresh ourselves about the parts 38 00:03:35,000 --> 00:03:40,000 of a flower. We've come inside because despite the fact that it's locked down, there are still 39 00:03:40,000 --> 00:03:46,000 buildings, two doors down, making a lot of noise in their back garden. And lots of people own their lawns, obviously, 40 00:03:46,000 --> 00:03:51,000 because it's been raining for three months. Finally, we've got a sunny day, so we've come inside to actually 41 00:03:51,000 --> 00:03:56,000 get some peace and quiet. And it's a really good time of year to remind ourselves about 42 00:03:56,000 --> 00:04:01,000 the parts of a flower, because there's a lot of very large flowers growing and spreading where you 43 00:04:01,000 --> 00:04:07,000 can actually see the parts quite easily. So I brought in three common flowers. 44 00:04:07,000 --> 00:04:12,000 There's a tulip, which I have to admit I didn't grow in my garden, has been sitting around in a vase getting 45 00:04:12,000 --> 00:04:17,000 old. There's a hellebore and there's a daffodil and narcissus. I'm going to start 46 00:04:17,000 --> 00:04:22,000 by looking at the tulip. So I'll just move these two out the way. 47 00:04:22,000 --> 00:04:28,000 So this is a tulip. These are the petals. And they are obviously dying now and falling 48 00:04:28,000 --> 00:04:33,000 back and now fall off. But the whole thing won't die because this green part in the middle here 49 00:04:33,000 --> 00:04:38,000 is the female part of the flower that's called a pistol. And around 50 00:04:38,000 --> 00:04:43,000 you can see these little black structures and those are the stamens. And the statements have a little stalk called 51 00:04:43,000 --> 00:04:48,000 a filaments. And then a black fuzzy have almost like a little microphone. And the fuzzy head is 52 00:04:48,000 --> 00:04:54,000 where all the pollen is. So this tulip is producing black pollen and you'll see that the stamens 53 00:04:54,000 --> 00:04:59,000 are quite a bit shorter than that and the pistol in the middle. This fancy top bit 54 00:04:59,000 --> 00:05:05,000 is called the stigma, and that's why the pollen lands. And then there's a style. And at the bottom 55 00:05:05,000 --> 00:05:10,000 there are the egg cells. So that's the tune that if we look at 56 00:05:10,000 --> 00:05:15,000 a daffodil. We can see something very similar. I'll just pull the trumpets apart so you can 57 00:05:15,000 --> 00:05:20,000 see inside. No problem. Breaking open. It's quite strong, actually. And again, 58 00:05:20,000 --> 00:05:25,000 we have a central single pistol sticking up and around it there are multiple 59 00:05:25,000 --> 00:05:31,000 stamens and they've got their little anthers, a yellow, much more familiar colour covered, a little 60 00:05:31,000 --> 00:05:37,000 sort of dusty yellow pollen. And finally, if I bring in this hellebore, 61 00:05:37,000 --> 00:05:42,000 you see something a little bit different. So it doesn't have just one stigma. Five 62 00:05:42,000 --> 00:05:47,000 here in a group, five pistols. I mean, it has a group of stamens 63 00:05:47,000 --> 00:05:53,000 around the outside. And you can see the way that they're sort of bending over for paying away. 64 00:05:53,000 --> 00:05:58,000 And the little top part that is the M4 that produces the pollen. So this is a typical 65 00:05:58,000 --> 00:06:03,000 structure for a hermaphrodite flower. And that's what most 66 00:06:03,000 --> 00:06:08,000 plants are. Most plants are hermaphrodites. We find Mabbett strange 67 00:06:08,000 --> 00:06:13,000 because, of course, mammals and humans are mammals. Not enough ridi where either male or female. 68 00:06:13,000 --> 00:06:19,000 But that's one of the unusual things about mammals really are lots of animals. Most plants 69 00:06:19,000 --> 00:06:26,000 are hermaphrodites. And that means they have both male and female parts. 70 00:06:26,000 --> 00:06:31,000 So what's unusual about primrose flowers is that they're not all the same. 71 00:06:31,000 --> 00:06:36,000 So there are two different types of primrose flowers that you can find a male called 72 00:06:36,000 --> 00:06:41,000 PIN and Throm. And I'm going to draw each one for you. 73 00:06:41,000 --> 00:06:46,000 So I want you to imagine that this is the primrose flower. And looking at it from the side, there's 74 00:06:46,000 --> 00:06:51,000 the stalk that supports it. Here's the flower. And imagine we've sliced it down and we 75 00:06:51,000 --> 00:06:57,000 can now look inside. We've just seen that most flowers are hermaphrodites. Primrose 76 00:06:57,000 --> 00:07:02,000 is no different. So it's going to have female and male parts. And the pen 77 00:07:02,000 --> 00:07:07,000 flower, the female part looks like this. We have the 78 00:07:07,000 --> 00:07:13,000 at the bottom there. There's the ovary with the unfertilised egg cells inside. 79 00:07:13,000 --> 00:07:18,000 And we have the long style. And on the top we have a little disk like stigma. 80 00:07:18,000 --> 00:07:24,000 And that's hoping that the pollen will land there and then the pollen tube will grow down the style 81 00:07:24,000 --> 00:07:29,000 and fertilise the cells. So that's the female part, the pesto. Now 82 00:07:29,000 --> 00:07:34,000 they're hermaphrodites. So they've also got male parts. So the stamens in the case of the 83 00:07:34,000 --> 00:07:40,000 pin flower are short. They only come about halfway up and that's 84 00:07:40,000 --> 00:07:46,000 why they're down there. And they've got the pollen on them. So that's what a pin flower looks like 85 00:07:46,000 --> 00:07:51,000 from flower. Looks rather different. So again, we'll just draw the 86 00:07:51,000 --> 00:07:57,000 flower itself. These are the petals as the stalk. And again, the cutaway, I am looking 87 00:07:57,000 --> 00:08:02,000 into the middle. And what we would see when we looked in to a thrummed 88 00:08:02,000 --> 00:08:07,000 flower is we wouldn't see this tall stigmata at the top. Instead, 89 00:08:07,000 --> 00:08:13,000 we would see a little group of five stamens and you just see the anthers 90 00:08:13,000 --> 00:08:19,000 at the top and the pollen then are quite close together and little tight bones and the stigma 91 00:08:19,000 --> 00:08:25,000 female part is all the way down here. So it's short. There's the stigma is the style. 92 00:08:25,000 --> 00:08:30,000 And we have the ovary in there of the exiles. So they 93 00:08:30,000 --> 00:08:35,000 have these very suspect strange system where they have two types of flower that are 94 00:08:35,000 --> 00:08:40,000 that look very different. And what's going on here is this is a way to ensure 95 00:08:40,000 --> 00:08:46,000 that PIN can't pollinate itself and nor can Throm. So what PIN 96 00:08:46,000 --> 00:08:51,000 is hoping is by having this long, tall stigma here is that pollen from a thrummed flower 97 00:08:51,000 --> 00:08:56,000 will be transferred across to a pen stigma by an insect. That would just stay 98 00:08:56,000 --> 00:09:01,000 at the top of the flower. But if an insect forages deeper into the flower, then it will pick up pollen 99 00:09:01,000 --> 00:09:07,000 from there, from the pen flower. And when it does, it's a Thram flower. It will put pollen onto that 100 00:09:07,000 --> 00:09:12,000 stigma. And that is what we call hetero smiley. We get these two morphs 101 00:09:12,000 --> 00:09:19,000 and they are designed to pollinate each other and not to allow self pollination. 102 00:09:19,000 --> 00:09:24,000 That is something that's actually quite common in plants. When we think about it, it's 103 00:09:24,000 --> 00:09:29,000 a little bit like having two different sexes. We have males and females. Males 104 00:09:29,000 --> 00:09:34,000 can only mate with females and females can only mate with males. And this is the same thing. Pins can 105 00:09:34,000 --> 00:09:39,000 only met with Thrums and Thrums can only make it with pins. But strangely enough, that's happening 106 00:09:39,000 --> 00:09:45,000 within a system where everyone is hermaphrodite, which makes you wonder 107 00:09:45,000 --> 00:09:51,000 which is the better system? Is it better from an evolutionary perspective to have two sexes? 108 00:09:51,000 --> 00:09:56,000 Or is it better to have this kind of cell phone compatibility? So we want 109 00:09:56,000 --> 00:10:01,000 to try and explain now some of the costs involved with sex and particularly 110 00:10:01,000 --> 00:10:07,000 the costs involved in producing males. So I want to imagine on this side 111 00:10:07,000 --> 00:10:12,000 is the sexual population and here is a single individual female. She's just arrived 112 00:10:12,000 --> 00:10:17,000 in a new environment. Perhaps she's a female fish who has only arrival 113 00:10:17,000 --> 00:10:22,000 in an enormous new pond or Asian. So she's got this opportunity to be incredibly 114 00:10:22,000 --> 00:10:28,000 successful. And this fish happens to be pregnant, which is even better. So she's going to be able to have offspring 115 00:10:28,000 --> 00:10:33,000 without there being a male present at the moment. Now, she can only have two offspring. We're 116 00:10:33,000 --> 00:10:38,000 going to assume one's going to be she now and one's going to be male. And as soon as she's had 117 00:10:38,000 --> 00:10:44,000 her offspring, she herself unfortunately dies. So we're just making some very simple assumptions. 118 00:10:44,000 --> 00:10:49,000 So in the next generation or two, fish in my pond and ones male ones female 119 00:10:49,000 --> 00:10:54,000 in the next generation, that female fish only is going to be able to have more 120 00:10:54,000 --> 00:10:59,000 offspring. But she's only going to be able to have two again, one female and one male. 121 00:10:59,000 --> 00:11:04,000 The males are important because they're fertilising the females and allowing them to have any offspring at 122 00:11:04,000 --> 00:11:10,000 all. But because they can't have offspring every generation, 123 00:11:10,000 --> 00:11:15,000 there's just two new fish, one female and one male. And this isn't really looking like a fantastic 124 00:11:15,000 --> 00:11:20,000 strategy. Now, of course, you could argue, well, but no fish can have only two offspring and 125 00:11:20,000 --> 00:11:26,000 indeed they can't. But I just want to illustrate the point, because we gonna compare. Dismay to what would happen 126 00:11:26,000 --> 00:11:31,000 if that female fish wasn't sexual but was asexual. So here 127 00:11:31,000 --> 00:11:36,000 is a single fish. A single female fish who's arrived in this pond and she's competing against the 128 00:11:36,000 --> 00:11:41,000 sexual female. But something's gone wrong in her genes so that she no longer has 129 00:11:41,000 --> 00:11:46,000 sex. She produces eggs where she just hands on all of 130 00:11:46,000 --> 00:11:51,000 her genetic material. And so they don't need fertilising by a male. And she, too, 131 00:11:51,000 --> 00:11:57,000 can only have two offspring. And then she dies. So in the first generation, there's her two female 132 00:11:57,000 --> 00:12:02,000 offspring and she's dead now. And the next generation, both of 133 00:12:02,000 --> 00:12:08,000 those females can produce two female offspring. So in the next generation, 134 00:12:08,000 --> 00:12:13,000 for this fish, there are now four of her offspring present. And 135 00:12:13,000 --> 00:12:18,000 each of those females can also produce two more offspring. 136 00:12:18,000 --> 00:12:23,000 And they're both going to be female and say in that generation, there's now 137 00:12:23,000 --> 00:12:28,000 going to be eight new fish, all female. And it's pretty 138 00:12:28,000 --> 00:12:34,000 easy to see when you compare the sexual side to the asexual side, which is more successful. 139 00:12:34,000 --> 00:12:39,000 The asexual side is able to outgrow the sexual population very 140 00:12:39,000 --> 00:12:44,000 easily. And this is one of the so-called costs of sex. It's the costs 141 00:12:44,000 --> 00:12:50,000 of producing males, which, although they are necessary in a sexual population to provide sperm, 142 00:12:50,000 --> 00:12:55,000 to fertilise eggs, they don't contribute to the population growth rate. 143 00:12:55,000 --> 00:13:00,000 And so it seems that producing males is a really costly strategy. 144 00:13:00,000 --> 00:13:06,000 So how do our primroses fit into this? Well, they're actually a little bit more like the asexual 145 00:13:06,000 --> 00:13:11,000 population. It's true that if a single primrose got into a fail, well, it can do very much. 146 00:13:11,000 --> 00:13:16,000 But if two individuals got in and one was Pennyman, a momma's throm, then they could cross pollinate each 147 00:13:16,000 --> 00:13:21,000 other. And crucially, both of those individuals would be able to produce seeds and therefore 148 00:13:21,000 --> 00:13:27,000 contribute offspring to the next generation. So their population could grow very rapidly, 149 00:13:27,000 --> 00:13:32,000 which really makes you wonder what's going on on the sexual side. Why do so many animals have a male 150 00:13:32,000 --> 00:13:37,000 and female system? Well, the answer to that is long and complicated. I don't want 151 00:13:37,000 --> 00:13:42,000 to go into it all now, but one of the key advantages of sex is so that you don't just 152 00:13:42,000 --> 00:13:47,000 produce clones of yourself. Instead, you mix your genetic material 153 00:13:47,000 --> 00:13:53,000 with that of other individuals in the population. Somehow that must generate a big enough advantage to 154 00:13:53,000 --> 00:13:58,000 offset some of these disadvantages. Of course, the primroses have got those 155 00:13:58,000 --> 00:14:03,000 advance just too, because by having this pen thrums system, they are forced 156 00:14:03,000 --> 00:14:08,000 to mix their genetic material with that of other individuals. But they're not paying 157 00:14:08,000 --> 00:14:13,000 all of the costs of sex, which animals are. So they've come up with something 158 00:14:13,000 --> 00:14:18,000 really clever. Perhaps it's not surprising that lots of plants have a system like the Primrose 159 00:14:18,000 --> 00:14:24,000 where there are two different types which can't make within themselves but can only make it across. 160 00:14:24,000 --> 00:14:29,000 They're not always appends Thrums system. There's different ways of making it happen, but it's much more common 161 00:14:29,000 --> 00:14:34,000 in plants than having separate males and females. There are a few plants that do that, but it's 162 00:14:34,000 --> 00:14:39,000 pretty rare. So it just goes to show. And that was drawn to plants or was thing a bit boring. 163 00:14:39,000 --> 00:14:44,000 They even got faces in the long queue. They do have some pretty cool biology. 164 00:14:44,000 --> 00:14:50,000 Let's try and end this piece where it began back in the lawn, whether primroses are growing. 165 00:14:50,000 --> 00:14:55,000 So what we learnt is that primroses have this really unusual mating system, which is a 166 00:14:55,000 --> 00:15:01,000 bit like having different sexes and certainly have some of the advantages of having different sexes. 167 00:15:01,000 --> 00:15:06,000 But by being hermaphrodites, they are actually able to avoid some of the costs of sex 168 00:15:06,000 --> 00:15:11,000 because they don't produce males who can't then contribute to the next generation. 169 00:15:11,000 --> 00:15:16,000 Well, I hope you at home are able to go outside, even if only a little bit during these very 170 00:15:16,000 --> 00:15:22,000 difficult times, and that you might be able to find some primroses growing in your garden or somewhere 171 00:15:22,000 --> 00:15:27,000 nearby. And if you do have a look inside the flowers to see if you can work out whether they're pen 172 00:15:27,000 --> 00:15:32,000 or whether they're throm, I got a quick look round my garden and that means they seem to be penned strangely and 173 00:15:32,000 --> 00:15:37,000 thrum, but its roots are very many of them cowslips. So exactly the same by the way. They also have a pen 174 00:15:37,000 --> 00:15:42,000 throm system so you can't find primroses but you can find cowslips, then you can do the 175 00:15:42,000 --> 00:15:51,160 same thing. All right. That's it for this time.