Marcus Byrne: The dance of the dung beetle

83,025 views ・ 2012-12-13

TED


Please double-click on the English subtitles below to play the video.

00:00
Translator: Joseph Geni Reviewer: Morton Bast
0
0
7000
00:15
This is poo,
1
15984
2248
00:18
and what I want to do today is share my passion
2
18232
2483
00:20
for poo with you,
3
20715
3143
00:23
which might be quite difficult,
4
23858
2813
00:26
but I think what you might find more fascinating
5
26671
3093
00:29
is the way these small animals deal with poo.
6
29764
3201
00:32
So this animal here has got a brain
7
32965
2352
00:35
about the size of a grain of rice, and yet it can do things
8
35317
3960
00:39
that you and I couldn't possibly entertain the idea of doing.
9
39277
3750
00:43
And basically it's all evolved to handle its food source,
10
43027
4122
00:47
which is dung.
11
47149
2134
00:49
So the question is, where do we start this story?
12
49283
2579
00:51
And it seems appropriate to start at the end,
13
51862
3025
00:54
because this is a waste product that comes out
14
54887
2785
00:57
of other animals, but it still contains nutrients
15
57672
3573
01:01
and there are sufficient nutrients in there
16
61245
1957
01:03
for dung beetles basically to make a living,
17
63202
2963
01:06
and so dung beetles eat dung, and their larvae
18
66165
2935
01:09
are also dung-feeders.
19
69100
2155
01:11
They are grown completely in a ball of dung.
20
71255
3230
01:14
Within South Africa, we've got about 800 species of dung beetles,
21
74485
3795
01:18
in Africa we've got 2,000 species of dung beetles,
22
78280
3270
01:21
and in the world we have about 6,000 species of dung beetles.
23
81550
4598
01:26
So, according to dung beetles, dung is pretty good.
24
86148
5138
01:31
Unless you're prepared to get dung under your fingernails
25
91286
2672
01:33
and root through the dung itself, you'll never see
26
93958
2769
01:36
90 percent of the dung beetle species,
27
96727
2291
01:39
because they go directly into the dung,
28
99018
2406
01:41
straight down below it, and then they shuttle back and forth
29
101424
2612
01:44
between the dung at the soil surface
30
104036
2055
01:46
and a nest they make underground.
31
106091
2940
01:49
So the question is, how do they deal with this material?
32
109031
5245
01:54
And most dung beetles actually wrap it into a package of some sort.
33
114276
3980
01:58
Ten percent of the species actually make a ball,
34
118256
3680
02:01
and this ball they roll away from the dung source,
35
121936
4162
02:06
usually bury it at a remote place away from the dung source,
36
126098
3436
02:09
and they have a very particular behavior
37
129534
3305
02:12
by which they are able to roll their balls.
38
132839
4975
02:17
So this is a very proud owner of a beautiful dung ball.
39
137814
3593
02:21
You can see it's a male
40
141407
1235
02:22
because he's got a little hair on the back of his legs there,
41
142642
2241
02:24
and he's clearly very pleased about what he's sitting on there.
42
144883
5069
02:29
And then he's about to become a victim
43
149952
1912
02:31
of a vicious smash-and-grab. (Laughter)
44
151864
5249
02:37
And this is a clear indication
45
157113
2698
02:39
that this is a valuable resource.
46
159811
2611
02:42
And so valuable resources have to be looked after
47
162422
4125
02:46
and guarded in a particular way, and we think
48
166547
3319
02:49
the reason they roll the balls away is because of this,
49
169866
3302
02:53
because of the competition that is involved
50
173168
2410
02:55
in getting hold of that dung.
51
175578
1875
02:57
So this dung pat was actually -- well, it was a dung pat
52
177453
3197
03:00
15 minutes before this photograph was taken,
53
180650
2446
03:03
and we think it's the intense competition
54
183096
3049
03:06
that makes the beetles so well-adapted
55
186145
3880
03:10
to rolling balls of dung.
56
190025
2689
03:12
So what you've got to imagine here is this animal here
57
192714
2033
03:14
moving across the African veld.
58
194747
3603
03:18
Its head is down. It's walking backwards.
59
198350
3348
03:21
It's the most bizarre way to actually transport your food in any particular direction,
60
201698
5371
03:27
and at the same time it's got to deal with the heat.
61
207069
2866
03:29
This is Africa. It's hot.
62
209935
1988
03:31
So what I want to share with you now
63
211923
1707
03:33
are some of the experiments that myself and my colleagues
64
213630
3175
03:36
have used to investigate how dung beetles
65
216805
4841
03:41
deal with these problems.
66
221646
2052
03:43
So watch this beetle,
67
223698
2537
03:46
and there's two things that I would like you to be aware of.
68
226235
4144
03:50
The first is how it deals with this obstacle
69
230379
2562
03:52
that we've put in its way. See, look, it does a little dance,
70
232941
2888
03:55
and then it carries on in exactly the same direction
71
235829
2934
03:58
that it took in the first place.
72
238763
3690
04:02
A little dance, and then heads off in a particular direction.
73
242453
3766
04:06
So clearly this animal knows where it's going
74
246219
3377
04:09
and it knows where it wants to go,
75
249596
1339
04:10
and that's a very, very important thing,
76
250935
1885
04:12
because if you think about it, you're at the dung pile,
77
252820
2415
04:15
you've got this great big pie that you want to get away from everybody else,
78
255235
4523
04:19
and the quickest way to do it is in a straight line.
79
259758
2893
04:22
So we gave them some more tasks to deal with,
80
262651
4379
04:27
and what we did here is we turned the world
81
267030
4160
04:31
under their feet. And watch its response.
82
271190
3679
04:40
So this animal has actually had the whole world
83
280547
2796
04:43
turned under its feet. It's turned by 90 degrees.
84
283343
2847
04:46
But it doesn't flinch. It knows exactly where it wants to go,
85
286190
2472
04:48
and it heads off in that particular direction.
86
288662
2968
04:51
So our next question then was,
87
291630
2192
04:53
how are they doing this?
88
293822
1960
04:55
What are they doing? And there was a cue that was available to us.
89
295782
3449
04:59
It was that every now and then they'd climb on top of the ball
90
299231
3127
05:02
and they'd take a look at the world around them.
91
302358
2632
05:04
And what do you think they could be looking at
92
304990
1720
05:06
as they climb on top of the ball?
93
306710
1676
05:08
What are the obvious cues that this animal could use
94
308386
3555
05:11
to direct its movement? And the most obvious one
95
311941
4178
05:16
is to look at the sky, and so we thought,
96
316119
4219
05:20
now what could they be looking at in the sky?
97
320338
2264
05:22
And the obvious thing to look at is the sun.
98
322602
4109
05:26
So a classic experiment here,
99
326711
2954
05:29
in that what we did was we moved the sun.
100
329665
3539
05:33
What we're going to do now is shade the sun with a board
101
333204
2741
05:35
and then move the sun with a mirror
102
335945
1970
05:37
to a completely different position.
103
337915
1866
05:39
And look at what the beetle does.
104
339781
1912
05:41
It does a little double dance,
105
341693
2831
05:44
and then it heads back in exactly the same direction
106
344524
2279
05:46
it went in the first place.
107
346803
2409
05:49
What happens now? So clearly they're looking at the sun.
108
349212
3727
05:52
The sun is a very important cue in the sky for them.
109
352939
3262
05:56
The thing is the sun is not always available to you,
110
356201
2625
05:58
because at sunset it disappears below the horizon.
111
358826
4416
06:03
What is happening in the sky here
112
363242
2584
06:05
is that there's a great big pattern of polarized light in the sky
113
365826
3659
06:09
that you and I can't see. It's the way our eyes are built.
114
369485
3751
06:13
But the sun is at the horizon over here
115
373236
3703
06:16
and we know that when the sun is at the horizon,
116
376939
2967
06:19
say it's over on this side,
117
379906
1544
06:21
there is a north-south, a huge pathway across the sky
118
381450
4585
06:26
of polarized light that we can't see
119
386035
2473
06:28
that the beetles can see.
120
388508
2798
06:31
So how do we test that? Well, that's easy.
121
391306
2859
06:34
What we do is we get a great big polarization filter,
122
394165
2942
06:37
pop the beetle underneath it, and the filter is at right angles
123
397107
4424
06:41
to the polarization pattern of the sky.
124
401531
2650
06:44
The beetle comes out from underneath the filter
125
404181
4170
06:48
and it does a right-hand turn,
126
408351
2503
06:50
because it comes back under the sky
127
410854
2194
06:53
that it was originally orientated to
128
413048
2819
06:55
and then reorientates itself back
129
415867
2345
06:58
to the direction it was originally going in.
130
418212
3922
07:02
So obviously beetles can see polarized light.
131
422134
5817
07:07
Okay, so what we've got so far is,
132
427951
2757
07:10
what are beetles doing? They're rolling balls.
133
430708
2776
07:13
How are they doing it? Well, they're rolling them in a straight line.
134
433484
3015
07:16
How are they maintaining it in a particular straight line?
135
436499
3578
07:20
Well, they're looking at celestial cues in the sky,
136
440077
2695
07:22
some of which you and I can't see.
137
442772
2244
07:25
But how do they pick up those celestial cues?
138
445016
1684
07:26
That was what was of interest to us next.
139
446700
3044
07:29
And it was this particular little behavior, the dance,
140
449744
3188
07:32
that we thought was important, because look,
141
452932
2919
07:35
it takes a pause every now and then,
142
455851
1556
07:37
and then heads off in the direction that it wants to go in.
143
457407
4479
07:41
So what are they doing when they do this dance?
144
461886
4237
07:46
How far can we push them before they will reorientate themselves?
145
466123
4342
07:50
And in this experiment here, what we did was we forced them
146
470465
3496
07:53
into a channel, and you can see he wasn't
147
473961
2662
07:56
particularly forced into this particular channel,
148
476623
2738
07:59
and we gradually displaced the beetle by 180 degrees
149
479361
5298
08:04
until this individual ends up going in exactly the opposite direction
150
484659
3736
08:08
that it wanted to go in, in the first place.
151
488395
2565
08:10
And let's see what his reaction is
152
490960
2801
08:13
as he's headed through 90 degrees here,
153
493761
2610
08:16
and now he's going to -- when he ends up down here,
154
496371
2104
08:18
he's going to be 180 degrees in the wrong direction.
155
498475
3047
08:21
And see what his response is.
156
501522
2298
08:23
He does a little dance, he turns around,
157
503820
3193
08:27
and heads back in this. He knows exactly where he's going.
158
507013
3734
08:30
He knows exactly what the problem is,
159
510747
2279
08:33
and he knows exactly how to deal with it,
160
513026
1595
08:34
and the dance is this transition behavior
161
514621
2701
08:37
that allows them to reorientate themselves.
162
517322
2809
08:40
So that's the dance, but after spending many years
163
520131
4792
08:44
sitting in the African bush watching dung beetles on nice hot days,
164
524923
3656
08:48
we noticed that there was another behavior
165
528579
2351
08:50
associated with the dance behavior.
166
530930
2489
08:53
Every now and then, when they climb on top of the ball,
167
533419
3938
08:57
they wipe their face.
168
537357
3406
09:00
And you see him do it again.
169
540763
2963
09:03
Now we thought, now what could be going on here?
170
543726
2981
09:06
Clearly the ground is very hot, and when the ground is hot,
171
546707
2904
09:09
they dance more often, and when they do this particular dance,
172
549611
2735
09:12
they wipe the bottom of their face.
173
552346
1970
09:14
And we thought that it could be a thermoregulatory behavior.
174
554316
2699
09:17
We thought that maybe what they're doing is trying to
175
557015
2010
09:19
get off the hot soil and also spitting onto their face
176
559025
3441
09:22
to cool their head down.
177
562466
2416
09:24
So what we did was design a couple of arenas.
178
564882
4442
09:29
one was hot, one was cold.
179
569324
2099
09:31
We shaded this one. We left that one hot.
180
571423
2377
09:33
And then what we did was we filmed them with a thermal camera.
181
573800
3467
09:37
So what you're looking at here is a heat image
182
577267
4416
09:41
of the system, and what you can see here emerging
183
581683
3921
09:45
from the poo is a cool dung ball.
184
585604
3609
09:49
So the truth is, if you look at the temperature over here,
185
589213
3279
09:52
dung is cool. (Laughter)
186
592492
4980
09:57
So all we're interested in here is comparing the temperature
187
597472
3218
10:00
of the beetle against the background.
188
600690
2640
10:03
So the background here is around about 50 degrees centigrade.
189
603330
3944
10:07
The beetle itself and the ball are probably around about
190
607274
2608
10:09
30 to 35 degrees centigrade,
191
609882
2071
10:11
so this is a great big ball of ice cream
192
611953
2666
10:14
that this beetle is now transporting across the hot veld.
193
614619
3127
10:17
It isn't climbing. It isn't dancing, because
194
617746
2703
10:20
its body temperature is actually relatively low.
195
620449
2841
10:23
It's about the same as yours and mine.
196
623290
3073
10:26
And what's of interest here is that little brain is quite cool.
197
626363
4964
10:31
But if we contrast now what happens in a hot environment,
198
631327
4307
10:35
look at the temperature of the soil.
199
635634
2150
10:37
It's up around 55 to 60 degrees centigrade.
200
637784
3450
10:41
Watch how often the beetle dances.
201
641234
3442
10:44
And look at its front legs. They're roaringly hot.
202
644676
4542
10:49
So the ball leaves a little thermal shadow,
203
649218
2923
10:52
and the beetle climbs on top of the ball
204
652141
1934
10:54
and wipes its face, and all the time it's trying to cool itself down,
205
654075
4639
10:58
we think, and avoid the hot sand that it's walking across.
206
658714
5670
11:04
And what we did then was put little boots on these legs,
207
664384
3932
11:08
because this was a way to test if the legs
208
668316
2962
11:11
were involved in sensing the temperature of the soil.
209
671278
3758
11:15
And if you look over here, with boots they climb onto the ball
210
675036
3977
11:19
far less often when they had no boots on.
211
679013
4191
11:23
So we described these as cool boots.
212
683204
2327
11:25
It was a dental compound that we used to make these boots.
213
685531
2922
11:28
And we also cooled down the dung ball, so we were able
214
688453
2887
11:31
to put the ball in the fridge, gave them a nice cool dung ball,
215
691340
3649
11:34
and they climbed onto that ball far less often
216
694989
2551
11:37
than when they had a hot ball.
217
697540
1536
11:39
So this is called stilting. It's a thermal behavior
218
699076
2974
11:42
that you and I do if we cross the beach,
219
702050
1908
11:43
we jump onto a towel, somebody has this towel --
220
703958
2718
11:46
"Sorry, I've jumped onto your towel." --
221
706676
1223
11:47
and then you scuttle across onto somebody else's towel,
222
707899
2564
11:50
and that way you don't burn your feet.
223
710463
2205
11:52
And that's exactly what the beetles are doing here.
224
712668
2801
11:55
However, there's one more story I'd like to share with you,
225
715469
3215
11:58
and that's this particular species.
226
718684
1572
12:00
It's from a genus called Pachysoma.
227
720256
2793
12:03
There are 13 species in the genus, and they have
228
723049
3032
12:06
a particular behavior that I think you will find interesting.
229
726081
6138
12:12
This is a dung beetle. Watch what he's doing.
230
732219
4660
12:16
Can you spot the difference?
231
736879
2690
12:19
They don't normally go this slowly. It's in slow motion.
232
739569
3232
12:22
but it's walking forwards,
233
742801
1794
12:24
and it's actually taking a pellet of dry dung with it.
234
744595
3561
12:28
This is a different species in the same genus
235
748156
2454
12:30
but exactly the same foraging behavior.
236
750610
3872
12:34
There's one more interesting aspect of this
237
754482
2791
12:37
dung beetle's behavior that we found quite fascinating,
238
757273
4303
12:41
and that's that it forages and provisions a nest.
239
761576
4506
12:46
So watch this individual here, and what he's trying to do
240
766082
2691
12:48
is set up a nest.
241
768773
2720
12:51
And he doesn't like this first position,
242
771493
1709
12:53
but he comes up with a second position,
243
773202
1623
12:54
and about 50 minutes later, that nest is finished,
244
774825
3857
12:58
and he heads off to forage and provision
245
778682
3727
13:02
at a pile of dry dung pellets.
246
782409
2354
13:04
And what I want you to notice is the outward path
247
784763
3166
13:07
compared to the homeward path, and compare the two.
248
787929
4609
13:12
And by and large, you'll see that the homeward path
249
792538
2660
13:15
is far more direct than the outward path.
250
795198
2831
13:18
On the outward path, he's always on the lookout
251
798029
2815
13:20
for a new blob of dung.
252
800844
2465
13:23
On the way home, he knows where home is,
253
803309
1551
13:24
and he wants to go straight to it.
254
804860
3218
13:28
The important thing here is that this is not a one-way trip,
255
808078
3575
13:31
as in most dung beetles. The trip here is repeated
256
811653
3390
13:35
back and forth between a provisioning site and a nest site.
257
815043
4305
13:39
And watch, you're going to see
258
819348
942
13:40
another South African crime taking place right now. (Laughter)
259
820290
4010
13:44
And his neighbor steals one of his dung pellets.
260
824300
4614
13:48
So what we're looking at here
261
828914
3137
13:52
is a behavior called path integration.
262
832051
3328
13:55
And what's taking place is that the beetle
263
835379
2617
13:57
has got a home spot, it goes out on a convoluted path
264
837996
4303
14:02
looking for food, and then when it finds food,
265
842299
3091
14:05
it heads straight home. It knows exactly where its home is.
266
845390
4308
14:09
Now there's two ways it could be doing that,
267
849698
3025
14:12
and we can test that by displacing the beetle
268
852723
2960
14:15
to a new position when it's at the foraging site.
269
855683
2697
14:18
If it's using landmarks, it will find its home.
270
858380
3294
14:21
If it is using something called path integration,
271
861674
3415
14:25
it will not find its home. It will arrive at the wrong spot,
272
865089
3784
14:28
and what it's doing here if it's using path integration
273
868873
2424
14:31
is it's counting its steps or measuring the distance out in this direction.
274
871297
3871
14:35
It knows the bearing home, and it knows it should be in that direction.
275
875168
3697
14:38
If you displace it, it ends up in the wrong place.
276
878865
3128
14:41
So let's see what happens when we put this beetle
277
881993
2577
14:44
to the test with a similar experiment.
278
884570
3316
14:47
So here's our cunning experimenter.
279
887886
4386
14:52
He displaces the beetle,
280
892272
2401
14:54
and now we have to see what is going to take place.
281
894673
4849
14:59
What we've got is a burrow. That's where the forage was.
282
899522
3094
15:02
The forage has been displaced to a new position.
283
902616
2947
15:05
If he's using landmark orientation,
284
905563
2359
15:07
he should be able to find the burrow,
285
907922
1760
15:09
because he'll be able to recognize the landmarks around it.
286
909682
2723
15:12
If he's using path integration,
287
912405
3043
15:15
then it should end up in the wrong spot over here.
288
915448
3724
15:19
So let's watch what happens
289
919172
2310
15:21
when we put the beetle through the whole test.
290
921482
3291
15:24
So there he is there.
291
924773
1996
15:26
He's about to head home, and look what happens.
292
926769
6260
15:33
Shame.
293
933029
2493
15:35
It hasn't a clue.
294
935522
2234
15:37
It starts to search for its house in the right distance
295
937756
2920
15:40
away from the food, but it is clearly completely lost.
296
940676
5975
15:46
So we know now that this animal uses path integration
297
946651
4218
15:50
to find its way around, and the callous experimenter
298
950869
4079
15:54
leads it top left and leaves it. (Laughter)
299
954948
3121
15:58
So what we're looking at here are a group of animals
300
958069
4055
16:02
that use a compass, and they use the sun as a compass
301
962124
2079
16:04
to find their way around,
302
964203
1640
16:05
and they have some sort of system
303
965843
2525
16:08
for measuring that distance,
304
968368
1963
16:10
and we know that these species here actually
305
970331
3337
16:13
count the steps. That's what they use as an odometer,
306
973668
2681
16:16
a step-counting system, to find their way back home.
307
976349
5137
16:21
We don't know yet what dung beetles use.
308
981486
2823
16:24
So what have we learned from these animals
309
984309
2279
16:26
with a brain that's the size of a grain of rice?
310
986588
3001
16:29
Well, we know that they can roll balls in a straight line
311
989589
4111
16:33
using celestial cues.
312
993700
2145
16:35
We know that the dance behavior is an orientation behavior
313
995845
3128
16:38
and it's also a thermoregulation behavior,
314
998973
2414
16:41
and we also know that they use a path integration system
315
1001387
4198
16:45
for finding their way home.
316
1005585
2089
16:47
So for a small animal dealing with a fairly revolting substance
317
1007674
4170
16:51
we can actually learn an awful lot from these things
318
1011844
2769
16:54
doing behaviors that you and I couldn't possibly do.
319
1014613
3632
16:58
Thank you. (Applause)
320
1018245
4000
About this website

This site will introduce you to YouTube videos that are useful for learning English. You will see English lessons taught by top-notch teachers from around the world. Double-click on the English subtitles displayed on each video page to play the video from there. The subtitles scroll in sync with the video playback. If you have any comments or requests, please contact us using this contact form.

https://forms.gle/WvT1wiN1qDtmnspy7