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.
Welcome to my first episode. Every episode is going to start with something that I can find in
my garden. The prime minister's just declared that we're all under lockdown. Nobody's
allowed to leave their house. Yes, they absolutely have to. So I'm going to have to be quite creative about the way we
make these videos. Today's episode is going to start with this flower here. This
is the common primrose. This is a native British flower. You can find it all over
the U.K. It's classic habitat is at the bottom of hedges. That's where it really likes to grow. It
doesn't like to be too dry and it doesn't like to be too wet. But it used to be enormously abundant
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
as people manage the Vergis better by the roads and motorways, they're really making a bit of a comeback.
And if we look again closely at one, what you can see here is this is a classic wild primrose
where each flower is on its own separate stalk and lurking behind it. Here's something
a bit unusual. I don't know how well we can see this by move those on that away.
We have a big, long stalk and a great cluster of flowers on the top. That's
not a classic primrose and it's something to do with hybridisation. So that primroses
as hybridise with some other flower and we can go and take a look at what the possible culprit
is. That's caused that in a moment. So we've come to another part of the garden where growing in a different
part of the lawn, we have another primula species. So the first thing we looked at was the common primrose.
That's Premolar Vulgaris. This is the Cowslip. That's Primula virus.
And you see that it's very different construction. So it has a single long stand and then a whole
bunch of flowers coming off the top, which is a little bit like that, ABBA and Primrose or so. And that's
because that ABBA and Primrose is almost certainly a hybrid between the primrose and the cowslip,
and those hybrids do occur naturally. And it forms something called an ox lip, which is actually quite a rare
thing to find in nature. And it has the structure of the cowslip, but the individual flowers are big
and it has the pale, buttery yellow colour of the primrose. And gardeners
are taking advantage of those things and may have produced hybrids in an incredible
and, frankly, hideous array of colours and size. So if you go to a garden centre,
you can buy things called polymorphous, and they are deliberate hybrids between cowslips
and primroses, which have been bred to have wacky colours, which, well, personally I don't really like.
Okay. So what we've seen is there are two native premolars is common, the primrose and the cowslip.
And the reason they're interesting is because they have a really cool mating system. And that's actually
what I want to talk about, the mating system of the primrose. So before we look at the strange
mating system of the primrose, I thought it'd be good to refresh ourselves about the parts
of a flower. We've come inside because despite the fact that it's locked down, there are still
buildings, two doors down, making a lot of noise in their back garden. And lots of people own their lawns, obviously,
because it's been raining for three months. Finally, we've got a sunny day, so we've come inside to actually
get some peace and quiet. And it's a really good time of year to remind ourselves about
the parts of a flower, because there's a lot of very large flowers growing and spreading where you
can actually see the parts quite easily. So I brought in three common flowers.
There's a tulip, which I have to admit I didn't grow in my garden, has been sitting around in a vase getting
old. There's a hellebore and there's a daffodil and narcissus. I'm going to start
by looking at the tulip. So I'll just move these two out the way.
So this is a tulip. These are the petals. And they are obviously dying now and falling
back and now fall off. But the whole thing won't die because this green part in the middle here
is the female part of the flower that's called a pistol. And around
you can see these little black structures and those are the stamens. And the statements have a little stalk called
a filaments. And then a black fuzzy have almost like a little microphone. And the fuzzy head is
where all the pollen is. So this tulip is producing black pollen and you'll see that the stamens
are quite a bit shorter than that and the pistol in the middle. This fancy top bit
is called the stigma, and that's why the pollen lands. And then there's a style. And at the bottom
there are the egg cells. So that's the tune that if we look at
a daffodil. We can see something very similar. I'll just pull the trumpets apart so you can
see inside. No problem. Breaking open. It's quite strong, actually. And again,
we have a central single pistol sticking up and around it there are multiple
stamens and they've got their little anthers, a yellow, much more familiar colour covered, a little
sort of dusty yellow pollen. And finally, if I bring in this hellebore,
you see something a little bit different. So it doesn't have just one stigma. Five
here in a group, five pistols. I mean, it has a group of stamens
around the outside. And you can see the way that they're sort of bending over for paying away.
And the little top part that is the M4 that produces the pollen. So this is a typical
structure for a hermaphrodite flower. And that's what most
plants are. Most plants are hermaphrodites. We find Mabbett strange
because, of course, mammals and humans are mammals. Not enough ridi where either male or female.
But that's one of the unusual things about mammals really are lots of animals. Most plants
are hermaphrodites. And that means they have both male and female parts.
So what's unusual about primrose flowers is that they're not all the same.
So there are two different types of primrose flowers that you can find a male called
PIN and Throm. And I'm going to draw each one for you.
So I want you to imagine that this is the primrose flower. And looking at it from the side, there's
the stalk that supports it. Here's the flower. And imagine we've sliced it down and we
can now look inside. We've just seen that most flowers are hermaphrodites. Primrose
is no different. So it's going to have female and male parts. And the pen
flower, the female part looks like this. We have the
at the bottom there. There's the ovary with the unfertilised egg cells inside.
And we have the long style. And on the top we have a little disk like stigma.
And that's hoping that the pollen will land there and then the pollen tube will grow down the style
and fertilise the cells. So that's the female part, the pesto. Now
they're hermaphrodites. So they've also got male parts. So the stamens in the case of the
pin flower are short. They only come about halfway up and that's
why they're down there. And they've got the pollen on them. So that's what a pin flower looks like
from flower. Looks rather different. So again, we'll just draw the
flower itself. These are the petals as the stalk. And again, the cutaway, I am looking
into the middle. And what we would see when we looked in to a thrummed
flower is we wouldn't see this tall stigmata at the top. Instead,
we would see a little group of five stamens and you just see the anthers
at the top and the pollen then are quite close together and little tight bones and the stigma
female part is all the way down here. So it's short. There's the stigma is the style.
And we have the ovary in there of the exiles. So they
have these very suspect strange system where they have two types of flower that are
that look very different. And what's going on here is this is a way to ensure
that PIN can't pollinate itself and nor can Throm. So what PIN
is hoping is by having this long, tall stigma here is that pollen from a thrummed flower
will be transferred across to a pen stigma by an insect. That would just stay
at the top of the flower. But if an insect forages deeper into the flower, then it will pick up pollen
from there, from the pen flower. And when it does, it's a Thram flower. It will put pollen onto that
stigma. And that is what we call hetero smiley. We get these two morphs
and they are designed to pollinate each other and not to allow self pollination.
That is something that's actually quite common in plants. When we think about it, it's
a little bit like having two different sexes. We have males and females. Males
can only mate with females and females can only mate with males. And this is the same thing. Pins can
only met with Thrums and Thrums can only make it with pins. But strangely enough, that's happening
within a system where everyone is hermaphrodite, which makes you wonder
which is the better system? Is it better from an evolutionary perspective to have two sexes?
Or is it better to have this kind of cell phone compatibility? So we want
to try and explain now some of the costs involved with sex and particularly
the costs involved in producing males. So I want to imagine on this side
is the sexual population and here is a single individual female. She's just arrived
in a new environment. Perhaps she's a female fish who has only arrival
in an enormous new pond or Asian. So she's got this opportunity to be incredibly
successful. And this fish happens to be pregnant, which is even better. So she's going to be able to have offspring
without there being a male present at the moment. Now, she can only have two offspring. We're
going to assume one's going to be she now and one's going to be male. And as soon as she's had
her offspring, she herself unfortunately dies. So we're just making some very simple assumptions.
So in the next generation or two, fish in my pond and ones male ones female
in the next generation, that female fish only is going to be able to have more
offspring. But she's only going to be able to have two again, one female and one male.
The males are important because they're fertilising the females and allowing them to have any offspring at
all. But because they can't have offspring every generation,
there's just two new fish, one female and one male. And this isn't really looking like a fantastic
strategy. Now, of course, you could argue, well, but no fish can have only two offspring and
indeed they can't. But I just want to illustrate the point, because we gonna compare. Dismay to what would happen
if that female fish wasn't sexual but was asexual. So here
is a single fish. A single female fish who's arrived in this pond and she's competing against the
sexual female. But something's gone wrong in her genes so that she no longer has
sex. She produces eggs where she just hands on all of
her genetic material. And so they don't need fertilising by a male. And she, too,
can only have two offspring. And then she dies. So in the first generation, there's her two female
offspring and she's dead now. And the next generation, both of
those females can produce two female offspring. So in the next generation,
for this fish, there are now four of her offspring present. And
each of those females can also produce two more offspring.
And they're both going to be female and say in that generation, there's now
going to be eight new fish, all female. And it's pretty
easy to see when you compare the sexual side to the asexual side, which is more successful.
The asexual side is able to outgrow the sexual population very
easily. And this is one of the so-called costs of sex. It's the costs
of producing males, which, although they are necessary in a sexual population to provide sperm,
to fertilise eggs, they don't contribute to the population growth rate.
And so it seems that producing males is a really costly strategy.
So how do our primroses fit into this? Well, they're actually a little bit more like the asexual
population. It's true that if a single primrose got into a fail, well, it can do very much.
But if two individuals got in and one was Pennyman, a momma's throm, then they could cross pollinate each
other. And crucially, both of those individuals would be able to produce seeds and therefore
contribute offspring to the next generation. So their population could grow very rapidly,
which really makes you wonder what's going on on the sexual side. Why do so many animals have a male
and female system? Well, the answer to that is long and complicated. I don't want
to go into it all now, but one of the key advantages of sex is so that you don't just
produce clones of yourself. Instead, you mix your genetic material
with that of other individuals in the population. Somehow that must generate a big enough advantage to
offset some of these disadvantages. Of course, the primroses have got those
advance just too, because by having this pen thrums system, they are forced
to mix their genetic material with that of other individuals. But they're not paying
all of the costs of sex, which animals are. So they've come up with something
really clever. Perhaps it's not surprising that lots of plants have a system like the Primrose
where there are two different types which can't make within themselves but can only make it across.
They're not always appends Thrums system. There's different ways of making it happen, but it's much more common
in plants than having separate males and females. There are a few plants that do that, but it's
pretty rare. So it just goes to show. And that was drawn to plants or was thing a bit boring.
They even got faces in the long queue. They do have some pretty cool biology.
Let's try and end this piece where it began back in the lawn, whether primroses are growing.
So what we learnt is that primroses have this really unusual mating system, which is a
bit like having different sexes and certainly have some of the advantages of having different sexes.
But by being hermaphrodites, they are actually able to avoid some of the costs of sex
because they don't produce males who can't then contribute to the next generation.
Well, I hope you at home are able to go outside, even if only a little bit during these very
difficult times, and that you might be able to find some primroses growing in your garden or somewhere
nearby. And if you do have a look inside the flowers to see if you can work out whether they're pen
or whether they're throm, I got a quick look round my garden and that means they seem to be penned strangely and
thrum, but its roots are very many of them cowslips. So exactly the same by the way. They also have a pen
throm system so you can't find primroses but you can find cowslips, then you can do the
same thing. All right. That's it for this time.