Subtitles and Transcript
00:11 If you'd like to learn how to play the lobster, we have some here. And that's not a joke, we really do. So come up afterwards and I'll show you how to play a lobster.
00:19 So, actually, I started working on what's called the mantis shrimp a few years ago because they make sound. This is a recording I made of a mantis shrimp that's found off the coast of California. And while that's an absolutely fascinating sound, it actually turns out to be a very difficult project. And while I was struggling to figure out how and why mantis shrimp, or stomatopods, make sound, I started to think about their appendages. And mantis shrimp are called "mantis shrimp" after the praying mantises, which also have a fast feeding appendage. And I started to think, well, maybe it will be interesting, while listening to their sounds, to figure out how these animals generate very fast feeding strikes. And so today I'll talk about the extreme stomatopod strike, work that I've done in collaboration with Wyatt Korff and Roy Caldwell.
01:16 So, mantis shrimp come in two varieties: there are spearers and smashers. And this is a spearing mantis shrimp, or stomatopod. And he lives in the sand, and he catches things that go by overhead. So, a quick strike like that. And if we slow it down a bit, this is the mantis shrimp -- the same species -- recorded at 1,000 frames a second, played back at 15 frames per second. And you can see it's just a really spectacular extension of the limbs, exploding upward to actually just catch a dead piece of shrimp that I had offered it. Now, the other type of mantis shrimp is the smasher stomatopod, and these guys open up snails for a living. And so this guy gets the snail all set up and gives it a good whack.
02:05 So, I'll play it one more time. He wiggles it in place, tugs it with his nose, and smash. And a few smashes later, the snail is broken open, and he's got a good dinner. So, the smasher raptorial appendage can stab with a point at the end, or it can smash with the heel. And today I'll talk about the smashing type of strike.
02:27 And so the first question that came to mind was, well, how fast does this limb move? Because it's moving pretty darn fast on that video. And I immediately came upon a problem. Every single high-speed video system in the biology department at Berkeley wasn't fast enough to catch this movement. We simply couldn't capture it on video. And so this had me stymied for quite a long period of time. And then a BBC crew came cruising through the biology department, looking for a story to do about new technologies in biology. And so we struck up a deal. I said, "Well, if you guys rent the high-speed video system that could capture these movements, you guys can film us collecting the data." And believe it or not, they went for it. (Laughter) So we got this incredible video system. It's very new technology -- it just came out about a year ago -- that allows you to film at extremely high speeds in low light. And low light is a critical issue with filming animals, because if it's too high, you fry them. (Laughter)
03:25 So this is a mantis shrimp. There are the eyes up here, and there's that raptorial appendage, and there's the heel. And that thing's going to swing around and smash the snail. And the snail's wired to a stick, so he's a little bit easier to set up the shot. And -- yeah.
03:43 I hope there aren't any snail rights activists around here.
03:48 So this was filmed at 5,000 frames per second, and I'm playing it back at 15. And so this is slowed down 333 times. And as you'll notice, it's still pretty gosh darn fast slowed down 333 times. It's an incredibly powerful movement. The whole limb extends out. The body flexes backwards -- just a spectacular movement. And so what we did is, we took a look at these videos, and we measured how fast the limb was moving to get back to that original question. And we were in for our first surprise. So what we calculated was that the limbs were moving at the peak speed ranging from 10 meters per second all the way up to 23 meters per second. And for those of you who prefer miles per hour, that's over 45 miles per hour in water. And this is really darn fast. In fact, it's so fast we were able to add a new point on the extreme animal movement spectrum. And mantis shrimp are officially the fastest measured feeding strike of any animal system. So our first surprise.
04:49 So that was really cool and very unexpected. So, you might be wondering, well, how do they do it? And actually, this work was done in the 1960s by a famous biologist named Malcolm Burrows. And what he showed in mantis shrimp is that they use what's called a "catch mechanism," or "click mechanism." And what this basically consists of is a large muscle that takes a good long time to contract, and a latch that prevents anything from moving. So the muscle contracts, and nothing happens. And once the muscle's contracted completely, everything's stored up -- the latch flies upward, and you've got the movement. And that's basically what's called a "power amplification system." It takes a long time for the muscle to contract, and a very short time for the limb to fly out. And so I thought that this was sort of the end of the story. This was how mantis shrimps make these very fast strikes.
05:38 But then I took a trip to the National Museum of Natural History. And if any of you ever have a chance, backstage of the National Museum of Natural History is one of the world's best collections of preserved mantis shrimp. And what --
05:51 this is serious business for me.
05:54 So, this -- what I saw, on every single mantis shrimp limb, whether it's a spearer or a smasher, is a beautiful saddle-shaped structure right on the top surface of the limb. And you can see it right here. It just looks like a saddle you'd put on a horse. It's a very beautiful structure. And it's surrounded by membranous areas. And those membranous areas suggested to me that maybe this is some kind of dynamically flexible structure. And this really sort of had me scratching my head for a while. And then we did a series of calculations, and what we were able to show is that these mantis shrimp have to have a spring. There needs to be some kind of spring-loaded mechanism in order to generate the amount of force that we observe, and the speed that we observe, and the output of the system. So we thought, OK, this must be a spring -- the saddle could very well be a spring. And we went back to those high-speed videos again, and we could actually visualize the saddle compressing and extending. And I'll just do that one more time. And then if you take a look at the video -- it's a little bit hard to see -- it's outlined in yellow. The saddle is outlined in yellow. You can actually see it extending over the course of the strike, and actually hyperextending. So, we've had very solid evidence showing that that saddle-shaped structure actually compresses and extends, and does, in fact, function as a spring.
07:13 The saddle-shaped structure is also known as a "hyperbolic paraboloid surface," or an "anticlastic surface." And this is very well known to engineers and architects, because it's a very strong surface in compression. It has curves in two directions, one curve upward and opposite transverse curve down the other, so any kind of perturbation spreads the forces over the surface of this type of shape. So it's very well known to engineers, not as well known to biologists. It's also known to quite a few people who make jewelry, because it requires very little material to build this type of surface, and it's very strong. So if you're going to build a thin gold structure, it's very nice to have it in a shape that's strong.
07:54 Now, it's also known to architects. One of the most famous architects is Eduardo Catalano, who popularized this structure. And what's shown here is a saddle-shaped roof that he built that's 87 and a half feet spanwise. It's two and a half inches thick, and supported at two points. And one of the reasons why he designed roofs this way is because it's -- he found it fascinating that you could build such a strong structure that's made of so few materials and can be supported by so few points. And all of these are the same principles that apply to the saddle-shaped spring in stomatopods. In biological systems it's important not to have a whole lot of extra material requirements for building it. So, very interesting parallels between the biological and the engineering worlds. And interestingly, this turns out -- the stomatopod saddle turns out to be the first described biological hyperbolic paraboloid spring. That's a bit long, but it is sort of interesting.
08:52 So the next and final question was, well, how much force does a mantis shrimp produce if they're able to break open snails? And so I wired up what's called a load cell. A load cell measures forces, and this is actually a piezoelectronic load cell that has a little crystal in it. And when this crystal is squeezed, the electrical properties change and it -- which -- in proportion to the forces that go in. So these animals are wonderfully aggressive, and are really hungry all the time. And so all I had to do was actually put a little shrimp paste on the front of the load cell, and they'd smash away at it. And so this is just a regular video of the animal just smashing the heck out of this load cell. And we were able to get some force measurements out. And again, we were in for a surprise.
09:35 I purchased a 100-pound load cell, thinking, no animal could produce more than 100 pounds at this size of an animal. And what do you know? They immediately overloaded the load cell. So these are actually some old data where I had to find the smallest animals in the lab, and we were able to measure forces of well over 100 pounds generated by an animal about this big. And actually, just last week I got a 300-pound load cell up and running, and I've clocked these animals generating well over 200 pounds of force. And again, I think this will be a world record. I have to do a little bit more background reading, but I think this will be the largest amount of force produced by an animal of a given -- per body mass. So, really incredible forces. And again, that brings us back to the importance of that spring in storing up and releasing so much energy in this system. But that was not the end of the story.
10:22 Now, things -- I'm making this sound very easy, this is actually a lot of work. And I got all these force measurements, and then I went and looked at the force output of the system. And this is just very simple -- time is on the X-axis and the force is on the Y-axis. And you can see two peaks. And that was what really got me puzzled. The first peak, obviously, is the limb hitting the load cell. But there's a really large second peak half a millisecond later, and I didn't know what that was. So now, you'd expect a second peak for other reasons, but not half a millisecond later. Again, going back to those high-speed videos, there's a pretty good hint of what might be going on. Here's that same orientation that we saw earlier. There's that raptorial appendage -- there's the heel, and it's going to swing around and hit the load cell. And what I'd like you to do in this shot is keep your eye on this, on the surface of the load cell, as the limb comes flying through. And I hope what you are able to see is actually a flash of light.
11:24 Audience: Wow.
11:26 Sheila Patek: And so if we just take that one frame, what you can actually see there at the end of that yellow arrow is a vapor bubble. And what that is, is cavitation. And cavitation is an extremely potent fluid dynamic phenomenon which occurs when you have areas of water moving at extremely different speeds. And when this happens, it can cause areas of very low pressure, which results in the water literally vaporizing. And when that vapor bubble collapses, it emits sound, light and heat, and it's a very destructive process. And so here it is in the stomatopod. And again, this is a situation where engineers are very familiar with this phenomenon, because it destroys boat propellers. People have been struggling for years to try and design a very fast rotating boat propeller that doesn't cavitate and literally wear away the metal and put holes in it, just like these pictures show.
12:18 So this is a potent force in fluid systems, and just to sort of take it one step further, I'm going to show you the mantis shrimp approaching the snail. This is taken at 20,000 frames per second, and I have to give full credit to the BBC cameraman, Tim Green, for setting this shot up, because I could never have done this in a million years -- one of the benefits of working with professional cameramen. You can see it coming in, and an incredible flash of light, and all this cavitation spreading over the surface of the snail. So really, just an amazing image, slowed down extremely, to extremely slow speeds. And again, we can see it in slightly different form there, with the bubble forming and collapsing between those two surfaces. In fact, you might have even seen some cavitation going up the edge of the limb.
13:11 So to solve this quandary of the two force peaks: what I think was going on is: that first impact is actually the limb hitting the load cell, and the second impact is actually the collapse of the cavitation bubble. And these animals may very well be making use of not only the force and the energy stored with that specialized spring, but the extremes of the fluid dynamics. And they might actually be making use of fluid dynamics as a second force for breaking the snail. So, really fascinating double whammy, so to speak, from these animals.
13:42 So, one question I often get after this talk -- so I figured I'd answer it now -- is, well, what happens to the animal? Because obviously, if it's breaking snails, the poor limb must be disintegrating. And indeed it does. That's the smashing part of the heel on both these images, and it gets worn away. In fact, I've seen them wear away their heel all the way to the flesh. But one of the convenient things about being an arthropod is that you have to molt. And every three months or so these animals molt, and they build a new limb and it's no problem. Very, very convenient solution to that particular problem.
14:15 So, I'd like to end on sort of a wacky note.
14:23 Maybe this is all wacky to folks like you, I don't know.
14:28 So, the saddles -- that saddle-shaped spring -- has actually been well known to biologists for a long time, not as a spring but as a visual signal. And there's actually a spectacular colored dot in the center of the saddles of many species of stomatopods. And this is quite interesting, to find evolutionary origins of visual signals on what's really, in all species, their spring. And I think one explanation for this could be going back to the molting phenomenon.
15:00 So these animals go into a molting period where they're unable to strike -- their bodies become very soft. And they're literally unable to strike or they will self-destruct. This is for real. And what they do is, up until that time period when they can't strike, they become really obnoxious and awful, and they strike everything in sight; it doesn't matter who or what. And the second they get into that time point when they can't strike any more, they just signal. They wave their legs around. And it's one of the classic examples in animal behavior of bluffing. It's a well-established fact of these animals that they actually bluff. They can't actually strike, but they pretend to. And so I'm very curious about whether those colored dots in the center of the saddles are conveying some kind of information about their ability to strike, or their strike force, and something about the time period in the molting cycle. So sort of an interesting strange fact to find a visual structure right in the middle of their spring.
16:00 So to conclude, I mostly want to acknowledge my two collaborators, Wyatt Korff and Roy Caldwell, who worked closely with me on this. And also the Miller Institute for Basic Research in Science, which gave me three years of funding to just do science all the time, and for that I'm very grateful. Thank you very much.