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, welcome to this episode of Background Biology. Today, we're going to be looking at colour,
something everybody's interested in and particularly how different kinds of colour are produced
with a special focus on a phenomenon called iridescence. Now, I was kind of inspired
in a slightly macabre way to make this particular video by this incident. I was called
to my next door neighbour over the fence. We have a little gate through a fence between
the back gardens as I was able to go through keeping my distance, of course. And she showed me this
rather macabre sight, an extraordinary thing.
A magpie drowned in a pond. And imagine that. Ever see that? Because they
seemed so smart, clever birds. That feels very sad, actually, to see it
so lifeless to try and get eggs. We don't want it to rot in the pond.
OK. So when I came back from looking at that, it made me think, wow, the magpie is a really beautiful
bird. And I hadn't fully realised how useful it was until I actually saw one lying face down that upon,
which is a little bit strange. But there we are. Now we buried the Magpies. We didn't want it to rot in the
pond. I just removed a small number of its feathers so that we could look at them more closely. So let's
have a close up on them. I've just got five of them here. A couple of tail feathers
and three of these wing feathers. What's interesting about the wing feathers is only half of
them have this iridescent quality. So you can see they are bluish.
And the colours appear to shift and change a bit as I move the feathers. The other half just look
like they're solid black. There are three feathers like that, and the tail feathers are a little
bit similar. They seem to have their more black on this side, but they have this iridescent
greenish bluish quality on the other side. So what's going on there?
Well, collar can be produced in different ways and one way that colour can be produced
is chemically through the use of pigments. And that's something we're quite familiar with. And we talked
about it in the episode about why the world was green. So if I just pick a typical leaf
here, this is from a Foxcroft plant that just happened to be growing. This leaf is green, and that's
because the chlorophyll in that is a pigment. It absorbs blue and red light and it
reflects green light. And so it looks green. And that's how pigments work. That's how all pigments
work because we saw again. And that said, why is the word green that the natural
light. Sunlight is actually made up of different colours and we see them when the light passes
through a prism and they are refracted. Okay, so that's how pigments were. But not all
colouration works like that. Some of it is what we call physical. So it's caused by physical structures
on the objects interfering with light, scattering light and refracting light
to create a different kind of effect. And that's how you can creative adolescence. You can't create
it with pigments. You have to create it with physical structures. Now, there's one or two examples
of physical colouration on one sitting next to me. And that's why untuck trauma's corner of the house. This is a
blue hosta. And you can see I've got this amazing bluish tenge. It doesn't look green.
And that's because it's covered in a special wax and that wax scatters blue light.
So that's a physical effect. It doesn't have a special blue pigment in it. It's scattering away blue light.
And in fact, if you leave it out in the sun, the wax degrades and it no longer looks blue and it just looks green.
Now, some other plants that like to grow in shade instead of being blue like that,
they have patterns on their leaves. Now, you might be used to seeing patterns on other kinds of
leaves, something called variegation. And here's an example of it where the leaves are both green
and white. Now, that's caused by pigments. The green parts are where the plants making chlorophyll
and the white parts are where the plant is not making chlorophyll, but some shade
leaves look a bit different. They've got this kind of mottled green and white patterns on them. And the whitish
bits are not due to a lack of chlorophyll. They're actually due to air pockets
that are trapped inside the leaves and that air bounces light
around inside the leaves. And we're not absolutely sure that's all about. But we think it's
a photo protective effect. So you think, well, what is a shade bluntly that is growing in the shade?
Well, it's because there's always some flax coming down through the canopy, shining a little bit of bright lights
onto a leaf. And that could be really damaging. And we think this ability to reflect light around
can help to prevent concentrated damage to the leaves. And there's one other really
cool way that plants can use structural colouration. And it really does produce genuine
iridescence. It's really rare, but there are just a small number of plants, a few begonia species
and a very weird plant called Selaginella that have this bluish sheen about
them, a blue iridescence, and that's caused by a very specialised chloroplast.
Those are the structures that. Contained normal chlorophyll implants. But they have these specially
adapted chloroplasts. They're called Everyday Plast. And they
are able to absorb some of that green light that the other plants aren't using. So if you imagine
you're right down at the bottom of a canopy, all the good light is gone. But if you can just capture some
of that green light that the other leaves don't want, then you might be able to get a little bit of an advantage.
So they are using that iridescence to make the best of the leftover light that the other
plants don't want. Okay, so that's how plump leaves can use structural
colouration. What about flowers? Well, most flower colours just come from
pigments. They are nice, solid colours like these rather attractive pinkie purple tulips
that I was growing up my garden earlier this year before they all dried up because sun's been shining forever.
But this is a special tulip. It's called Queen of Light and it's a very dark
tulip. But you can see it's also an iridescent tulip. It sort of shines and greens
and the colours seem to change slightly as the viewing angles shifts. Why
do some flowers want to be iridescent? Well, they want to attract insects and insects might be more
sensitive to that iridescence because a lot of them are iridescent and some plants use that
to this in a deceptive way. So this is a bee orchid. And that is mimicking
a bee trying to attract a bee to come and pollinate. It is not going to offer it any nectar.
It's just deceiving the bee on the fly orchids. Does the same fly
orchid is actually adapted to attract male Dicko wasps, and it produces pheromones
that smell a female a wasps, and it's shiny and iridescent. So it looks like the shining
bodies of female wasps. So plants can be pretty tricky as we know.
So plants can use structural colour variation. But the real masters of structural
colour, not plants. Of course they are insects. So
how have insects become masters of iridescence? Well, the first thing to say about insects
is they have a great advantage when it comes to structural colouration because they have what's called an exo
skeleton. So we have an endoskeleton, the bones, the hard bits or on the insides and the soft, fleshy bits
are around those. But an insect is the other way around. So it's got the soft bits on the inside and it's covered
in like a suit of armour, which is the exoskeleton. And that's made from a compound
called chitin. And chitin can be sculpted incredibly finely. And
some insects have managed to produce multiple layers of chitin,
very close together, just a quarter of the wavelength of visible light apart.
Imagine a little stack of layers. And that's how they can create iridescence, because from
each of those layers, a very specific wavelength is reflected back. And the effect
of all those layers reflecting very specific wavelengths can create this intensity
of colour so that things look metallic and Gleen and pigments just
can't produce that kind of same intensity of colour. Now, some insects don't use iridescence.
Of course, beetles are very famous for using it, but there are also beetles like these liley
beetles that just are quite dull looking just plain red. For example, a map comes from pigments,
but other beetles really use iridescence to the max. And one of them can be quite easily seen in gardens, at
least in the south. Southern parts of England. So this is the Rose Chafer. And I found while wandering
around on my Hawthorne Bushes a bit earlier in the year, but also one on a rose flower very,
very recently, just in the last couple of days. And they the adults are just chomping on the pollen. So they're not going
to damage your roses. Don't worry about it. The larvae feed in rotting, decaying
wood. So it's not an insect that you have to consider a pest in any way. And it's really
beautiful. Now, the other kind of green beetle I'm seeing a lot of my garden right now is
something called the Swirl and Fire Beetle, which is a funny name. But the adult males, as you can see,
do have these amazing swollen thighs. They're not present in the females and they're also kind of a metallic green.
And I see them flying around in the long grass in parts of the law. I don't know. The females
lack the swollen thighs. That means it's a sexually active character. So the males
have the swollen thighs they can grip onto the females when they're meeting. But we found a dead female on the windowsill
in the front. And we put it under the microscope. And here you can see how she's still even in death.
She cleans and incredible colours of green and gold. It's not just beetles.
This is a green bottle, the type of fly, something that you don't really want inside your house. But actually, its colours
are utterly stunning. Another type of insect that's very famous for employing iridescence
are the butterflies. So the morpho butterflies that live in the tropics have an intense blue colouration.
And our peacock butterfly, which you might find in your garden, also deploys iridescence in those
amazing eye spots. So finally, we need to ask why we always need to
ask why we did that for the plants as well, why do they bother to produce iridescence? We need to ask the same thing for the
insects. Well, there's various possibilities about how iridescence could help insects.
It could be for Krip says often insects, iridescent insects are amazing green colour. And perhaps
that does help them to hide. Or other people have said it's about confusing visual predators. So,
yes, you think it's highly visible, this metallic insect from a distance as it's flying,
but then once it lands, it seems to have disappeared because the angle of the light has changed and it's just vanished
into the vegetation. And the final reason is for what we call sexual selection. So
that's a character that's evolved to help an animal or an organism get mates
rather than to increase its own survival chances. But one of the things you have to do in order to get
high fitness, you have to have offspring, and that means getting mating opportunities.
And we see a lot of sexual selection going on amongst the damsel flies and dragonflies. That's
an order of insects called the odour after some of them have solid colouration like
this common blue damsel fly. But some of them have incredible iridescence and some of those
flying around right now. So it's two species that we see quite commonly in the U.K. The beautiful demoiselle
and the banded them was my uncle went off to find some banded demoiselles at
a stream near him in Lincolnshire and came back with these lovely footage. So here is a male banded
demoiselle sitting by the river with these beautiful, striking blue colouration.
He is very brightly coloured. We think to hold territories, to fight with other males, to compete
for the females. The females are also iridescent, but it's a much more muted
tone. It's a greenish tone. But as he was filming this one, this happened.
And this is a hairy dragonfly who just launched himself at this female, pulled her head off and started
eating in front of him. So, you know, iridescence is there's definitely risks that things are taking
as well. It does make things rather conspicuous. And if that's a bit too macabre, in
my own garden, I see this wonderful jewel wasp or ruby tails or WASP, and she
hangs around the bean, the Bee Hotel. She is a cuckoo bee, a cuckoo
wasps are is not a bee. She is a true wasp. But she's looking to parasitise the nests
of mason bees. And Mason was going to lay her eggs in there and her larvae are going to hatch
and they're going to eat the food, they eat the larvae of the bee. So she's pretty predatory herself. But
on this occasion she got caught out because she was nosing around the Bee Hotel and got caught in a spider's
web and the spider rushed out to grab her. And here that is again in slow motion.
The spider decided that she was too much to handle and let her go. But I was glad about
because in a she is really one of the most spectacular insects that you can see. Even though she's tiny,
she's absolutely beautiful. The last thing we're going to do is just hear
from Leon Crowley again, that's well known until I suggest he take some incredible photographs
of insects. And he's just going to give us a little taste of some of his favourite iridescent insects.
Hello. So, yeah, I'm just going to give some examples of iridescent insects
which are with you. My favourite nose. So many insects, which are doesn't it's really hard to choose.
So he's just a few examples. No, they lepidopterists not just butterflies, which have
iridescent scales. And as you can see with this yellow board longhorn moth on this narrow boarded
five spot burning moth. And they have spectacular iridescence them
with them beetles. There's many, many examples of iridescence, probably the most of any group,
but most people wouldn't necessarily associate these beautiful iridescence with
dung beetles. But as you can see here, this door beetle is very shiny and
iridescent. And then with Hymenoptera. There
are bees which are iridescent on this, the cuticle, the surface
of that skeleton. We don't we say it because of that long has, which are characteristic bees.
And as you can see with this Ozma, a bee that can be very reduction. And if only
I just wanted to give some appreciation to flies, which, as we said, can be very
iridescent and such as the blowfly you saw earlier. And this is another species
of California day. So in the same family, there is a cluster fly and spectacular
golden iridescence here. So that's it for about God and biology this
week. I hope you can find some of these incredible iridescent things around
your garden, whether it's insects or birds or plants. All kinds of things
are refracting and reflecting and playing with light in order to dazzle their
enemies, the dazzle of their sexual partners or intimidate their rivals.
You know, put up plants and animals alike are masters of iridescence.