1
00:00:00,330 --> 00:00:05,640
Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences

2
00:00:05,640 --> 00:00:10,770
at the University of Oxford, and we're right in the middle of this very serious corona virus crisis right

3
00:00:10,770 --> 00:00:15,810
now. And my students are all stuck at home and we want to keep them in touch with biology

4
00:00:15,810 --> 00:00:21,240
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
00:00:21,240 --> 00:00:47,210
biology.

6
00:00:47,210 --> 00:00:52,310
Hello, welcome to this episode of Background Biology. Today, we're going to be looking at colour,

7
00:00:52,310 --> 00:00:57,470
something everybody's interested in and particularly how different kinds of colour are produced

8
00:00:57,470 --> 00:01:02,660
with a special focus on a phenomenon called iridescence. Now, I was kind of inspired

9
00:01:02,660 --> 00:01:07,910
in a slightly macabre way to make this particular video by this incident. I was called

10
00:01:07,910 --> 00:01:13,010
to my next door neighbour over the fence. We have a little gate through a fence between

11
00:01:13,010 --> 00:01:18,230
the back gardens as I was able to go through keeping my distance, of course. And she showed me this

12
00:01:18,230 --> 00:01:24,120
rather macabre sight, an extraordinary thing.

13
00:01:24,120 --> 00:01:29,210
A magpie drowned in a pond. And imagine that. Ever see that? Because they

14
00:01:29,210 --> 00:01:34,590
seemed so smart, clever birds. That feels very sad, actually, to see it

15
00:01:34,590 --> 00:01:40,770
so lifeless to try and get eggs. We don't want it to rot in the pond.

16
00:01:40,770 --> 00:01:46,130
OK. So when I came back from looking at that, it made me think, wow, the magpie is a really beautiful

17
00:01:46,130 --> 00:01:51,320
bird. And I hadn't fully realised how useful it was until I actually saw one lying face down that upon,

18
00:01:51,320 --> 00:01:56,420
which is a little bit strange. But there we are. Now we buried the Magpies. We didn't want it to rot in the

19
00:01:56,420 --> 00:02:01,490
pond. I just removed a small number of its feathers so that we could look at them more closely. So let's

20
00:02:01,490 --> 00:02:06,930
have a close up on them. I've just got five of them here. A couple of tail feathers

21
00:02:06,930 --> 00:02:12,050
and three of these wing feathers. What's interesting about the wing feathers is only half of

22
00:02:12,050 --> 00:02:17,450
them have this iridescent quality. So you can see they are bluish.

23
00:02:17,450 --> 00:02:22,820
And the colours appear to shift and change a bit as I move the feathers. The other half just look

24
00:02:22,820 --> 00:02:28,130
like they're solid black. There are three feathers like that, and the tail feathers are a little

25
00:02:28,130 --> 00:02:33,320
bit similar. They seem to have their more black on this side, but they have this iridescent

26
00:02:33,320 --> 00:02:40,160
greenish bluish quality on the other side. So what's going on there?

27
00:02:40,160 --> 00:02:45,230
Well, collar can be produced in different ways and one way that colour can be produced

28
00:02:45,230 --> 00:02:50,600
is chemically through the use of pigments. And that's something we're quite familiar with. And we talked

29
00:02:50,600 --> 00:02:55,700
about it in the episode about why the world was green. So if I just pick a typical leaf

30
00:02:55,700 --> 00:03:00,830
here, this is from a Foxcroft plant that just happened to be growing. This leaf is green, and that's

31
00:03:00,830 --> 00:03:05,900
because the chlorophyll in that is a pigment. It absorbs blue and red light and it

32
00:03:05,900 --> 00:03:10,940
reflects green light. And so it looks green. And that's how pigments work. That's how all pigments

33
00:03:10,940 --> 00:03:16,010
work because we saw again. And that said, why is the word green that the natural

34
00:03:16,010 --> 00:03:21,020
light. Sunlight is actually made up of different colours and we see them when the light passes

35
00:03:21,020 --> 00:03:26,090
through a prism and they are refracted. Okay, so that's how pigments were. But not all

36
00:03:26,090 --> 00:03:31,550
colouration works like that. Some of it is what we call physical. So it's caused by physical structures

37
00:03:31,550 --> 00:03:36,710
on the objects interfering with light, scattering light and refracting light

38
00:03:36,710 --> 00:03:41,780
to create a different kind of effect. And that's how you can creative adolescence. You can't create

39
00:03:41,780 --> 00:03:47,210
it with pigments. You have to create it with physical structures. Now, there's one or two examples

40
00:03:47,210 --> 00:03:52,250
of physical colouration on one sitting next to me. And that's why untuck trauma's corner of the house. This is a

41
00:03:52,250 --> 00:03:57,470
blue hosta. And you can see I've got this amazing bluish tenge. It doesn't look green.

42
00:03:57,470 --> 00:04:02,960
And that's because it's covered in a special wax and that wax scatters blue light.

43
00:04:02,960 --> 00:04:08,210
So that's a physical effect. It doesn't have a special blue pigment in it. It's scattering away blue light.

44
00:04:08,210 --> 00:04:14,090
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.

45
00:04:14,090 --> 00:04:19,310
Now, some other plants that like to grow in shade instead of being blue like that,

46
00:04:19,310 --> 00:04:24,320
they have patterns on their leaves. Now, you might be used to seeing patterns on other kinds of

47
00:04:24,320 --> 00:04:29,690
leaves, something called variegation. And here's an example of it where the leaves are both green

48
00:04:29,690 --> 00:04:35,510
and white. Now, that's caused by pigments. The green parts are where the plants making chlorophyll

49
00:04:35,510 --> 00:04:40,700
and the white parts are where the plant is not making chlorophyll, but some shade

50
00:04:40,700 --> 00:04:45,890
leaves look a bit different. They've got this kind of mottled green and white patterns on them. And the whitish

51
00:04:45,890 --> 00:04:50,900
bits are not due to a lack of chlorophyll. They're actually due to air pockets

52
00:04:50,900 --> 00:04:56,060
that are trapped inside the leaves and that air bounces light

53
00:04:56,060 --> 00:05:01,070
around inside the leaves. And we're not absolutely sure that's all about. But we think it's

54
00:05:01,070 --> 00:05:06,410
a photo protective effect. So you think, well, what is a shade bluntly that is growing in the shade?

55
00:05:06,410 --> 00:05:11,570
Well, it's because there's always some flax coming down through the canopy, shining a little bit of bright lights

56
00:05:11,570 --> 00:05:16,790
onto a leaf. And that could be really damaging. And we think this ability to reflect light around

57
00:05:16,790 --> 00:05:21,830
can help to prevent concentrated damage to the leaves. And there's one other really

58
00:05:21,830 --> 00:05:27,320
cool way that plants can use structural colouration. And it really does produce genuine

59
00:05:27,320 --> 00:05:32,900
iridescence. It's really rare, but there are just a small number of plants, a few begonia species

60
00:05:32,900 --> 00:05:38,000
and a very weird plant called Selaginella that have this bluish sheen about

61
00:05:38,000 --> 00:05:43,430
them, a blue iridescence, and that's caused by a very specialised chloroplast.

62
00:05:43,430 --> 00:05:48,890
Those are the structures that. Contained normal chlorophyll implants. But they have these specially

63
00:05:48,890 --> 00:05:54,290
adapted chloroplasts. They're called Everyday Plast. And they

64
00:05:54,290 --> 00:05:59,480
are able to absorb some of that green light that the other plants aren't using. So if you imagine

65
00:05:59,480 --> 00:06:04,550
you're right down at the bottom of a canopy, all the good light is gone. But if you can just capture some

66
00:06:04,550 --> 00:06:10,190
of that green light that the other leaves don't want, then you might be able to get a little bit of an advantage.

67
00:06:10,190 --> 00:06:15,380
So they are using that iridescence to make the best of the leftover light that the other

68
00:06:15,380 --> 00:06:20,780
plants don't want. Okay, so that's how plump leaves can use structural

69
00:06:20,780 --> 00:06:25,820
colouration. What about flowers? Well, most flower colours just come from

70
00:06:25,820 --> 00:06:31,080
pigments. They are nice, solid colours like these rather attractive pinkie purple tulips

71
00:06:31,080 --> 00:06:36,380
that I was growing up my garden earlier this year before they all dried up because sun's been shining forever.

72
00:06:36,380 --> 00:06:41,450
But this is a special tulip. It's called Queen of Light and it's a very dark

73
00:06:41,450 --> 00:06:46,760
tulip. But you can see it's also an iridescent tulip. It sort of shines and greens

74
00:06:46,760 --> 00:06:51,800
and the colours seem to change slightly as the viewing angles shifts. Why

75
00:06:51,800 --> 00:06:56,840
do some flowers want to be iridescent? Well, they want to attract insects and insects might be more

76
00:06:56,840 --> 00:07:02,360
sensitive to that iridescence because a lot of them are iridescent and some plants use that

77
00:07:02,360 --> 00:07:07,430
to this in a deceptive way. So this is a bee orchid. And that is mimicking

78
00:07:07,430 --> 00:07:13,220
a bee trying to attract a bee to come and pollinate. It is not going to offer it any nectar.

79
00:07:13,220 --> 00:07:18,410
It's just deceiving the bee on the fly orchids. Does the same fly

80
00:07:18,410 --> 00:07:23,870
orchid is actually adapted to attract male Dicko wasps, and it produces pheromones

81
00:07:23,870 --> 00:07:29,270
that smell a female a wasps, and it's shiny and iridescent. So it looks like the shining

82
00:07:29,270 --> 00:07:34,670
bodies of female wasps. So plants can be pretty tricky as we know.

83
00:07:34,670 --> 00:07:40,010
So plants can use structural colour variation. But the real masters of structural

84
00:07:40,010 --> 00:07:45,090
colour, not plants. Of course they are insects. So

85
00:07:45,090 --> 00:07:50,460
how have insects become masters of iridescence? Well, the first thing to say about insects

86
00:07:50,460 --> 00:07:55,670
is they have a great advantage when it comes to structural colouration because they have what's called an exo

87
00:07:55,670 --> 00:08:00,840
skeleton. So we have an endoskeleton, the bones, the hard bits or on the insides and the soft, fleshy bits

88
00:08:00,840 --> 00:08:06,030
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

89
00:08:06,030 --> 00:08:11,040
in like a suit of armour, which is the exoskeleton. And that's made from a compound

90
00:08:11,040 --> 00:08:16,170
called chitin. And chitin can be sculpted incredibly finely. And

91
00:08:16,170 --> 00:08:21,360
some insects have managed to produce multiple layers of chitin,

92
00:08:21,360 --> 00:08:26,460
very close together, just a quarter of the wavelength of visible light apart.

93
00:08:26,460 --> 00:08:31,560
Imagine a little stack of layers. And that's how they can create iridescence, because from

94
00:08:31,560 --> 00:08:36,600
each of those layers, a very specific wavelength is reflected back. And the effect

95
00:08:36,600 --> 00:08:41,700
of all those layers reflecting very specific wavelengths can create this intensity

96
00:08:41,700 --> 00:08:46,800
of colour so that things look metallic and Gleen and pigments just

97
00:08:46,800 --> 00:08:52,380
can't produce that kind of same intensity of colour. Now, some insects don't use iridescence.

98
00:08:52,380 --> 00:08:57,600
Of course, beetles are very famous for using it, but there are also beetles like these liley

99
00:08:57,600 --> 00:09:03,120
beetles that just are quite dull looking just plain red. For example, a map comes from pigments,

100
00:09:03,120 --> 00:09:08,160
but other beetles really use iridescence to the max. And one of them can be quite easily seen in gardens, at

101
00:09:08,160 --> 00:09:13,590
least in the south. Southern parts of England. So this is the Rose Chafer. And I found while wandering

102
00:09:13,590 --> 00:09:18,630
around on my Hawthorne Bushes a bit earlier in the year, but also one on a rose flower very,

103
00:09:18,630 --> 00:09:23,700
very recently, just in the last couple of days. And they the adults are just chomping on the pollen. So they're not going

104
00:09:23,700 --> 00:09:28,920
to damage your roses. Don't worry about it. The larvae feed in rotting, decaying

105
00:09:28,920 --> 00:09:34,320
wood. So it's not an insect that you have to consider a pest in any way. And it's really

106
00:09:34,320 --> 00:09:39,360
beautiful. Now, the other kind of green beetle I'm seeing a lot of my garden right now is

107
00:09:39,360 --> 00:09:44,550
something called the Swirl and Fire Beetle, which is a funny name. But the adult males, as you can see,

108
00:09:44,550 --> 00:09:50,070
do have these amazing swollen thighs. They're not present in the females and they're also kind of a metallic green.

109
00:09:50,070 --> 00:09:55,350
And I see them flying around in the long grass in parts of the law. I don't know. The females

110
00:09:55,350 --> 00:10:00,510
lack the swollen thighs. That means it's a sexually active character. So the males

111
00:10:00,510 --> 00:10:06,000
have the swollen thighs they can grip onto the females when they're meeting. But we found a dead female on the windowsill

112
00:10:06,000 --> 00:10:11,280
in the front. And we put it under the microscope. And here you can see how she's still even in death.

113
00:10:11,280 --> 00:10:16,560
She cleans and incredible colours of green and gold. It's not just beetles.

114
00:10:16,560 --> 00:10:21,780
This is a green bottle, the type of fly, something that you don't really want inside your house. But actually, its colours

115
00:10:21,780 --> 00:10:27,330
are utterly stunning. Another type of insect that's very famous for employing iridescence

116
00:10:27,330 --> 00:10:33,270
are the butterflies. So the morpho butterflies that live in the tropics have an intense blue colouration.

117
00:10:33,270 --> 00:10:38,310
And our peacock butterfly, which you might find in your garden, also deploys iridescence in those

118
00:10:38,310 --> 00:10:43,390
amazing eye spots. So finally, we need to ask why we always need to

119
00:10:43,390 --> 00:10:48,430
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

120
00:10:48,430 --> 00:10:53,590
insects. Well, there's various possibilities about how iridescence could help insects.

121
00:10:53,590 --> 00:10:58,630
It could be for Krip says often insects, iridescent insects are amazing green colour. And perhaps

122
00:10:58,630 --> 00:11:03,970
that does help them to hide. Or other people have said it's about confusing visual predators. So,

123
00:11:03,970 --> 00:11:09,310
yes, you think it's highly visible, this metallic insect from a distance as it's flying,

124
00:11:09,310 --> 00:11:14,470
but then once it lands, it seems to have disappeared because the angle of the light has changed and it's just vanished

125
00:11:14,470 --> 00:11:19,480
into the vegetation. And the final reason is for what we call sexual selection. So

126
00:11:19,480 --> 00:11:24,580
that's a character that's evolved to help an animal or an organism get mates

127
00:11:24,580 --> 00:11:29,590
rather than to increase its own survival chances. But one of the things you have to do in order to get

128
00:11:29,590 --> 00:11:34,600
high fitness, you have to have offspring, and that means getting mating opportunities.

129
00:11:34,600 --> 00:11:39,610
And we see a lot of sexual selection going on amongst the damsel flies and dragonflies. That's

130
00:11:39,610 --> 00:11:44,650
an order of insects called the odour after some of them have solid colouration like

131
00:11:44,650 --> 00:11:49,940
this common blue damsel fly. But some of them have incredible iridescence and some of those

132
00:11:49,940 --> 00:11:55,720
flying around right now. So it's two species that we see quite commonly in the U.K. The beautiful demoiselle

133
00:11:55,720 --> 00:12:01,180
and the banded them was my uncle went off to find some banded demoiselles at

134
00:12:01,180 --> 00:12:06,640
a stream near him in Lincolnshire and came back with these lovely footage. So here is a male banded

135
00:12:06,640 --> 00:12:12,760
demoiselle sitting by the river with these beautiful, striking blue colouration.

136
00:12:12,760 --> 00:12:18,070
He is very brightly coloured. We think to hold territories, to fight with other males, to compete

137
00:12:18,070 --> 00:12:23,410
for the females. The females are also iridescent, but it's a much more muted

138
00:12:23,410 --> 00:12:28,820
tone. It's a greenish tone. But as he was filming this one, this happened.

139
00:12:28,820 --> 00:12:34,150
And this is a hairy dragonfly who just launched himself at this female, pulled her head off and started

140
00:12:34,150 --> 00:12:39,400
eating in front of him. So, you know, iridescence is there's definitely risks that things are taking

141
00:12:39,400 --> 00:12:44,470
as well. It does make things rather conspicuous. And if that's a bit too macabre, in

142
00:12:44,470 --> 00:12:49,600
my own garden, I see this wonderful jewel wasp or ruby tails or WASP, and she

143
00:12:49,600 --> 00:12:54,760
hangs around the bean, the Bee Hotel. She is a cuckoo bee, a cuckoo

144
00:12:54,760 --> 00:12:59,860
wasps are is not a bee. She is a true wasp. But she's looking to parasitise the nests

145
00:12:59,860 --> 00:13:04,870
of mason bees. And Mason was going to lay her eggs in there and her larvae are going to hatch

146
00:13:04,870 --> 00:13:10,540
and they're going to eat the food, they eat the larvae of the bee. So she's pretty predatory herself. But

147
00:13:10,540 --> 00:13:15,670
on this occasion she got caught out because she was nosing around the Bee Hotel and got caught in a spider's

148
00:13:15,670 --> 00:13:21,550
web and the spider rushed out to grab her. And here that is again in slow motion.

149
00:13:21,550 --> 00:13:26,590
The spider decided that she was too much to handle and let her go. But I was glad about

150
00:13:26,590 --> 00:13:32,050
because in a she is really one of the most spectacular insects that you can see. Even though she's tiny,

151
00:13:32,050 --> 00:13:37,200
she's absolutely beautiful. The last thing we're going to do is just hear

152
00:13:37,200 --> 00:13:42,480
from Leon Crowley again, that's well known until I suggest he take some incredible photographs

153
00:13:42,480 --> 00:13:48,810
of insects. And he's just going to give us a little taste of some of his favourite iridescent insects.

154
00:13:48,810 --> 00:13:53,910
Hello. So, yeah, I'm just going to give some examples of iridescent insects

155
00:13:53,910 --> 00:13:59,050
which are with you. My favourite nose. So many insects, which are doesn't it's really hard to choose.

156
00:13:59,050 --> 00:14:04,050
So he's just a few examples. No, they lepidopterists not just butterflies, which have

157
00:14:04,050 --> 00:14:09,150
iridescent scales. And as you can see with this yellow board longhorn moth on this narrow boarded

158
00:14:09,150 --> 00:14:14,320
five spot burning moth. And they have spectacular iridescence them

159
00:14:14,320 --> 00:14:20,190
with them beetles. There's many, many examples of iridescence, probably the most of any group,

160
00:14:20,190 --> 00:14:25,200
but most people wouldn't necessarily associate these beautiful iridescence with

161
00:14:25,200 --> 00:14:30,450
dung beetles. But as you can see here, this door beetle is very shiny and

162
00:14:30,450 --> 00:14:35,580
iridescent. And then with Hymenoptera. There

163
00:14:35,580 --> 00:14:40,650
are bees which are iridescent on this, the cuticle, the surface

164
00:14:40,650 --> 00:14:46,320
of that skeleton. We don't we say it because of that long has, which are characteristic bees.

165
00:14:46,320 --> 00:14:51,510
And as you can see with this Ozma, a bee that can be very reduction. And if only

166
00:14:51,510 --> 00:14:56,640
I just wanted to give some appreciation to flies, which, as we said, can be very

167
00:14:56,640 --> 00:15:01,890
iridescent and such as the blowfly you saw earlier. And this is another species

168
00:15:01,890 --> 00:15:07,440
of California day. So in the same family, there is a cluster fly and spectacular

169
00:15:07,440 --> 00:15:12,590
golden iridescence here. So that's it for about God and biology this

170
00:15:12,590 --> 00:15:17,780
week. I hope you can find some of these incredible iridescent things around

171
00:15:17,780 --> 00:15:22,870
your garden, whether it's insects or birds or plants. All kinds of things

172
00:15:22,870 --> 00:15:28,040
are refracting and reflecting and playing with light in order to dazzle their

173
00:15:28,040 --> 00:15:33,430
enemies, the dazzle of their sexual partners or intimidate their rivals.

174
00:15:33,430 --> 00:15:52,400
You know, put up plants and animals alike are masters of iridescence.