WEBVTT - The Lesser of Two Crab Claws, Part 2 0:00:03.040 --> 0:00:05.360 Welcome to stot to Blow Your Mind production of My 0:00:05.480 --> 0:00:14.800 Heart Radio. Hey you welcome to Stuff to Blow Your Mind. 0:00:14.880 --> 0:00:17.560 My name is Robert Lamb and I'm Joe McCormick, and 0:00:17.640 --> 0:00:20.200 we're back with part two of our series on a 0:00:20.520 --> 0:00:24.920 Symmetry in Life Now. In the last episode, we talked 0:00:24.920 --> 0:00:28.760 about the concept of bilateral symmetry, where basically all of 0:00:28.800 --> 0:00:32.479 the higher animals have body plans where the left and 0:00:32.520 --> 0:00:35.440 the right sides are more or less a copy of 0:00:35.440 --> 0:00:38.920 one another. In other words, along one of the three 0:00:38.960 --> 0:00:42.600 dimensions of space, our bodies are approximately mirrored, at least 0:00:42.640 --> 0:00:46.599 on the outside. Now. Uh, In most organisms there are 0:00:46.800 --> 0:00:51.120 minor variations on this type of symmetry, but occasionally there 0:00:51.120 --> 0:00:56.440 are species with isolated but radical deviations, where like one 0:00:56.720 --> 0:01:00.600 feature on the outside of an otherwise mirror were flipped 0:01:00.640 --> 0:01:03.880 half of the body is drastically different from what you 0:01:03.920 --> 0:01:06.559 find on the other side. Examples that came up last 0:01:06.600 --> 0:01:09.680 time where the tusk of the nar wall, where in 0:01:09.800 --> 0:01:15.560 most cases it's actually the left maxillary canine tooth, So 0:01:15.600 --> 0:01:20.200 weirds the left fang basically of this whale stabbing through 0:01:20.240 --> 0:01:23.200 the upper lip and it becomes a single tusk. We 0:01:23.240 --> 0:01:26.640 also talked about the blowholes and skulls of toothed whales 0:01:26.720 --> 0:01:29.839 such as the sperm whale, where in many cases these 0:01:29.840 --> 0:01:34.399 have developed left right mismatches that seemed to have evolved 0:01:34.800 --> 0:01:39.119 to support the capacity for echolocation. We also talked about 0:01:39.120 --> 0:01:42.319 the cock eyed squid, which has two extremely different eyes 0:01:42.480 --> 0:01:46.000 for looking into extremely different worlds, one for the water above, 0:01:46.160 --> 0:01:49.520 which is filtering sunlight, and one for the water below, 0:01:49.640 --> 0:01:53.480 which may contain flashes of bioluminescence. And so today we 0:01:53.520 --> 0:01:55.480 wanted to pick up the series by talking about some 0:01:55.560 --> 0:02:00.760 more fascinating examples of lopsided animal evolution. Animal with halves 0:02:00.800 --> 0:02:04.280 that mostly match but in one capacity or another do not, 0:02:04.720 --> 0:02:07.520 and why that would be. Now, there are many great 0:02:07.560 --> 0:02:12.720 examples of of asymmetrical evolution in crustations, and we may 0:02:12.760 --> 0:02:14.840 actually save some of these for the next part in 0:02:14.840 --> 0:02:16.440 the series. I know we're going to go to at 0:02:16.480 --> 0:02:19.520 least three parts here, but for for today's episode, I 0:02:19.560 --> 0:02:22.160 wanted to start by getting out the lemon and the 0:02:22.240 --> 0:02:26.400 drawn butter, because this is an asymmetry that you don't 0:02:26.480 --> 0:02:30.120 have to be a specialist marine biologist to notice for yourself. 0:02:30.520 --> 0:02:34.480 If you've ever eaten or even just seen a cooked lobster. 0:02:35.280 --> 0:02:39.839 You probably have noticed a weird mismatch between the lobsters 0:02:39.960 --> 0:02:45.760 to clause Robert, I assume you've you've seen this for yourself, Yes, yes, Um, 0:02:46.080 --> 0:02:48.400 they're not not as recently as you have, because I 0:02:48.440 --> 0:02:51.240 believe this, uh, this was the inspiration for this episode, right, 0:02:51.280 --> 0:02:53.480 you recently ate a lobster? Oh, I don't. I don't 0:02:53.480 --> 0:02:55.320 think I even told you that, but yeah, this probably 0:02:55.320 --> 0:02:57.480 had something to do with it. I I can't confirm 0:02:57.680 --> 0:03:00.919 the inner workings of my subconscious mind. But not too 0:03:00.960 --> 0:03:02.960 long ago, I was in the I was in New 0:03:03.040 --> 0:03:06.040 England where where lobster is king. I'm not gonna do 0:03:06.040 --> 0:03:09.200 do the accent, but lobster is king. Uh. And I did, 0:03:09.200 --> 0:03:12.320 And I did, in fact eat a lobster. And yeah, 0:03:12.360 --> 0:03:15.640 and I noticed stark differences between the claws, even not 0:03:15.760 --> 0:03:18.240 just looking at them, but in my fingers, you know. 0:03:18.320 --> 0:03:21.480 One claw was was sort of a pleasure to crack 0:03:21.560 --> 0:03:23.359 open and get the meat out of, and the other 0:03:23.400 --> 0:03:27.359 one when I handled the inside of the pincers, Uh, 0:03:27.400 --> 0:03:30.560 they were much sharper and and the spines within them 0:03:30.600 --> 0:03:34.639 were much smaller and kind of we're irritating and unpleasant 0:03:34.639 --> 0:03:37.680 to the fingers. Fascinating. So what's going on with this 0:03:37.720 --> 0:03:39.720 claw mismatch? Oh and by the way, we should be 0:03:39.720 --> 0:03:43.080 clear that we're talking specifically about the American lobster or 0:03:43.720 --> 0:03:46.520 home marus americanus. This is the lobster you find along 0:03:46.560 --> 0:03:50.240 the northern edge of the eastern coast of North America, 0:03:50.320 --> 0:03:53.440 so all up through like the north half of the 0:03:53.480 --> 0:03:56.880 eastern United States and up into Canada. This is like 0:03:56.920 --> 0:04:00.760 the red lobster lobster, the lobster from your grocery store 0:04:00.800 --> 0:04:02.760 that has rubber bands on its claws, not like the 0:04:02.760 --> 0:04:06.200 Caribbean lobster. Yea, not the rock lobster, though I hear 0:04:06.240 --> 0:04:08.720 those can be good eating too, I've never had one. 0:04:08.760 --> 0:04:12.280 But anyway, so the American lobster. Uh. So, you look 0:04:12.320 --> 0:04:14.880 at these two claws, and what you'll notice is that 0:04:15.200 --> 0:04:20.880 usually one claw is longer and flatter, with a longer 0:04:21.480 --> 0:04:23.240 I don't know what the technical term for this is 0:04:23.279 --> 0:04:27.200 the danger zone, the space between the two pincers and 0:04:27.279 --> 0:04:30.359 the insides of the pincers. On this flatter, longer claws 0:04:30.360 --> 0:04:33.200 seemed to be sharper, more like a kind of spiky 0:04:33.279 --> 0:04:37.159 pair of scissors. And then the other claw is shorter 0:04:37.360 --> 0:04:41.520 in length, but bulkier, thick with muscle, and the inside 0:04:41.600 --> 0:04:45.400 edges of its pincers have a sort of rounder, larger 0:04:45.440 --> 0:04:50.719 grain texture, almost pebbled, rather than with tiny spines. These 0:04:50.760 --> 0:04:55.160 claws are commonly referred to as the cutter and the crusher, respectively. 0:04:55.279 --> 0:04:58.000 I think the cutter is sometimes called the pincher also, 0:04:58.440 --> 0:05:00.479 But yeah, that they are what they sound like, the 0:05:00.480 --> 0:05:03.120 cutter and the crusher. So what's going on? Why the 0:05:03.200 --> 0:05:06.880 two different claws on the same lobster. How does a 0:05:06.920 --> 0:05:09.400 lobster end up with two very different claws and what 0:05:09.480 --> 0:05:11.839 are they for? Well? To answer this question, I was 0:05:11.880 --> 0:05:14.760 reading what I thought was a really interesting older article 0:05:15.240 --> 0:05:19.200 in American Scientist magazine. So this is from ninety nine 0:05:19.680 --> 0:05:24.000 by an author named C. K. Govind, who was a 0:05:24.040 --> 0:05:27.880 professor of zoology at the University of Toronto, and it's 0:05:27.920 --> 0:05:31.960 called a symmetry in lobster claus Seems like a lot 0:05:32.040 --> 0:05:37.080 of Govin's research focused on crustaceans, and so Govin begins 0:05:37.120 --> 0:05:39.640 by pointing out a number of different examples of a 0:05:39.760 --> 0:05:43.800 symmetry and animals. He talks about lateral dominance or handedness 0:05:43.800 --> 0:05:47.320 in humans and even mentioned I thought this was interesting. 0:05:47.400 --> 0:05:51.520 Some in some songbirds, such as canaries, you have bilateral 0:05:51.600 --> 0:05:56.080 asymmetry in their singing apparatus. Song production seems to be 0:05:56.080 --> 0:05:59.599 centered on structures in the left half of the cy rinks. 0:06:00.120 --> 0:06:03.440 And so when you see asymmetries like this, uh, you 0:06:03.440 --> 0:06:05.440 can ask all kinds of questions about them. But one 0:06:05.440 --> 0:06:08.480 thing is that you might just assume them to be permanent, 0:06:08.760 --> 0:06:13.320 fixed features of anatomy, hard coded by genes and express 0:06:13.360 --> 0:06:17.479 their early development. But it's interesting that there are some 0:06:17.600 --> 0:06:21.479 cases where a symmetry in an animal's body seems to 0:06:21.520 --> 0:06:25.080 be reversible. Just for one example, in some cases of 0:06:25.160 --> 0:06:29.000 lateral dominance, damage to the dominant side of the brain 0:06:29.120 --> 0:06:33.000 or body can cause the non dominant side to assume 0:06:33.200 --> 0:06:36.680 some functionality previously localized to the side that has now 0:06:36.760 --> 0:06:40.039 been incapacitated. And this can lead us to wonder how 0:06:40.200 --> 0:06:44.520 do these asymmetries develop in the first place. So Govind 0:06:44.720 --> 0:06:47.240 argues that by examining the lobster, and this is the 0:06:47.279 --> 0:06:51.560 American lobster Homarus americans, we can see an example of 0:06:51.600 --> 0:06:56.280 a symmetry emerging not purely as a result of genetic coding, 0:06:56.279 --> 0:06:59.799 but actually as a result of how the lobster interacts 0:06:59.800 --> 0:07:04.480 with it's with its environment during a crucial early period. Uh. 0:07:04.560 --> 0:07:06.400 And this is what brings us back to the crusher 0:07:06.440 --> 0:07:09.039 claw and the cutter claw. So I want to read 0:07:09.120 --> 0:07:14.440 from Govin's introduction here quote, as any self respecting gourmet knows, 0:07:14.560 --> 0:07:18.360 the paired claws of the American lobster have decidedly different morphologies. 0:07:18.920 --> 0:07:22.760 One claw, called the crusher or major claw, is short, stout, 0:07:22.800 --> 0:07:26.480 and heavy, with Moehler like teeth on its biting surface. 0:07:26.600 --> 0:07:29.240 I think that's a good comparison, moler like teeth. It's 0:07:29.520 --> 0:07:32.240 the pebbles are like your back teeth. It's hard to 0:07:32.280 --> 0:07:35.160 imagine them snipping something off. Instead, it seems like they 0:07:35.160 --> 0:07:37.720 would sort of grab hold of it and be able 0:07:37.720 --> 0:07:41.120 to smash it real good. Yeah. When when I'm looking 0:07:41.120 --> 0:07:42.760 at a picture of this, I can't help but imagine 0:07:42.760 --> 0:07:46.560 the lobster putting on a puppet show with with just 0:07:46.720 --> 0:07:48.800 its pincher and its crusher, and each of them have 0:07:48.880 --> 0:07:51.240 you know, different characters, like like like hey on the 0:07:51.280 --> 0:07:54.520 crutchery on the pincher, and they interact. You know. Definitely 0:07:54.520 --> 0:07:57.160 the cutter claw has the higher voice. Yeah, let's say 0:07:57.200 --> 0:08:00.320 if they're street fighter characters, crusher claw is zang gef 0:08:00.440 --> 0:08:03.840 and cutter claw is is what maybe maybe im bison 0:08:05.480 --> 0:08:09.520 longer does that cheap spinning move. Yeah, um okay, so anyway, 0:08:09.560 --> 0:08:11.480 so that that's what that is. That that's the molar 0:08:11.520 --> 0:08:14.400 teeth on the biting surface. But then, uh, to continue 0:08:14.440 --> 0:08:17.440 the quote, the other called the cutter or minor claw 0:08:17.560 --> 0:08:20.840 is long and slender with incisor like teeth, or your 0:08:20.880 --> 0:08:23.360 incisors are your front teeth, the ones that you use 0:08:23.440 --> 0:08:26.920 to bite off things. You know, not to mash them up, 0:08:26.960 --> 0:08:29.920 but to to separate them from what they're originally stuck 0:08:29.960 --> 0:08:33.080 to and pull them into your mouth there for cutting. Uh. 0:08:33.160 --> 0:08:36.040 So what Govind writes his quote, what the gourmet might 0:08:36.200 --> 0:08:39.840 may not know, and what lobstermen know painfully well, is 0:08:39.880 --> 0:08:44.200 that the cutter claw can give a quick, nasty pinch. Indeed, 0:08:44.280 --> 0:08:47.160 it's dactyl, meaning the part of the claw that moves, 0:08:47.280 --> 0:08:51.240 the closing part can close against the opposing polyx within 0:08:51.320 --> 0:08:56.119 twenty milliseconds, which is several times faster than any human reflex. 0:08:56.559 --> 0:09:00.720 In contrast, the crusher claw closes very slowly, but with 0:09:00.840 --> 0:09:04.840 enough force to crack open the shells of oysters, muscles, 0:09:04.840 --> 0:09:08.640 and other bivalves. Uh. And it's true mollusks such as 0:09:08.760 --> 0:09:11.880 muscles are a big source of food prey for the 0:09:11.920 --> 0:09:14.880 American lobsters. So it crawls along the ocean floor in 0:09:14.880 --> 0:09:17.240 its adult phase. And what does it eat. Well, it 0:09:17.320 --> 0:09:21.360 might eat some some worms of various types and stuff, 0:09:21.400 --> 0:09:24.479 but it's it's really going to be looking for mollusks 0:09:24.559 --> 0:09:26.960 such as muscles. It wants to crack those shells open 0:09:27.200 --> 0:09:30.800 and get that meat inside. Also, while we're mentioning anatomy, 0:09:30.840 --> 0:09:33.520 I this is unrelated, but I just have to say 0:09:33.679 --> 0:09:36.600 American lobsters do p out of their faces. You kind 0:09:36.600 --> 0:09:39.679 of can't bring lobsters up without mentioning that they face 0:09:39.760 --> 0:09:43.480 pe and they face peace, specifically at each other, whether 0:09:43.520 --> 0:09:46.280 it's a mate or rival. So lobster sees another lobster, 0:09:46.480 --> 0:09:48.920 they're probably gonna be peeing out of their faces at them. 0:09:49.240 --> 0:09:51.600 Uh though, is best I can tell. The face peeing 0:09:51.800 --> 0:09:55.040 is symmetrical. Okay, well that's good enough. But coming back 0:09:55.080 --> 0:09:57.560 to the clause, So the difference in the speed of 0:09:57.600 --> 0:10:00.480 pinching between the two claws is ev sense of an 0:10:00.559 --> 0:10:03.440 underlying difference and not just the shape of the claw, 0:10:03.840 --> 0:10:08.280 but it's muscular composition. These these claws have different types 0:10:08.320 --> 0:10:11.400 of muscle in them. About nine percent of the space 0:10:11.440 --> 0:10:14.800 of a lobster's claw is taken up by the closer muscle. 0:10:15.200 --> 0:10:18.320 This is the muscle responsible for bringing the pincers together. 0:10:18.880 --> 0:10:23.040 Only a relatively tiny muscle is devoted to opening the claw, 0:10:23.400 --> 0:10:25.600 which is why a lobster might be able to pinch 0:10:25.679 --> 0:10:29.120 with massive force, but a simple rubber band can render 0:10:29.160 --> 0:10:32.040 its claw harmless by holding it closed. It has way 0:10:32.080 --> 0:10:34.880 more strength for closing than it does for opening. Interacting. 0:10:34.960 --> 0:10:37.560 That's a great point. Yeah, I didn't double check this, 0:10:37.640 --> 0:10:40.480 but I just remembered hearing a fact that may or 0:10:40.480 --> 0:10:46.200 may not be true about alligator and crocodilian jaws like 0:10:46.240 --> 0:10:48.040 that when I was a kid. That you know, So 0:10:48.120 --> 0:10:50.680 they can close their jaws with massive force, but you 0:10:50.679 --> 0:10:53.640 can actually quite easily hold their jaws together with and 0:10:53.760 --> 0:10:56.080 they can't open them back up. So this would be 0:10:56.120 --> 0:11:02.160 the secret of the feet of the crocodile or alligator wrestler. Yes, okay, 0:11:02.280 --> 0:11:04.240 Now coming back to the lobster, does that mean that 0:11:04.280 --> 0:11:06.760 the closer muscle is the delicious part? This is like 0:11:06.800 --> 0:11:09.760 that prize sliver of meat from the claw. Well, I 0:11:09.960 --> 0:11:12.880 don't know about relative flavors. The closer would be the 0:11:12.920 --> 0:11:15.320 big one, and the the opener is obviously you know, 0:11:15.360 --> 0:11:18.320 it's like ten percent, it's like one ninth the size 0:11:18.320 --> 0:11:21.080 of the closer muscle. So I don't know exactly what 0:11:21.120 --> 0:11:23.200 you're getting. When you have a cooked lobster and you 0:11:23.240 --> 0:11:24.959 pull it out of there and eat it, you're probably 0:11:25.000 --> 0:11:27.960 some combination of the two. Well, I I guess in 0:11:28.000 --> 0:11:30.120 my experience, like the bigger the meat you pull out 0:11:30.120 --> 0:11:34.880 of a crustacean like the greater distance of victory. And likewise, 0:11:35.200 --> 0:11:38.439 the more that one is picking through the crustacean with 0:11:39.080 --> 0:11:43.679 and removing tiny slivers to consume that delicious they may be. 0:11:44.400 --> 0:11:46.440 But the more I feel like I'm some sort of 0:11:47.240 --> 0:11:52.280 like a creature stooped on a primordial shore scavenging pieces 0:11:52.320 --> 0:11:55.320 from a dead animal. Getting the pieces from the tiny 0:11:55.400 --> 0:11:57.360 legs and the tiny parts makes you feel more like 0:11:57.440 --> 0:12:00.679 it's the road. You know, you're like looking for seeds 0:12:00.800 --> 0:12:02.920 or something to eat, But pulling out that big piece 0:12:02.920 --> 0:12:05.520 of claw meat you feel like a king. That's right, 0:12:05.920 --> 0:12:08.839 that's luxury. Okay, So you got these different muscles. You 0:12:08.880 --> 0:12:11.880 got the closer muscle, the opener muscle. What what makes 0:12:11.920 --> 0:12:14.880 the difference in the speed of pinching between the crusher 0:12:14.920 --> 0:12:18.120 claw and the cutter claw is the type of muscle 0:12:18.240 --> 0:12:21.920 fiber that the closing muscle is composed of. The cutter 0:12:22.000 --> 0:12:26.320 claw is made of about fast muscle fiber, which is 0:12:26.400 --> 0:12:29.440 exactly what it sounds like. It's designed to move quickly 0:12:30.280 --> 0:12:34.200 along with what Govind calls a quote small ventral band 0:12:34.360 --> 0:12:38.600 of slow muscle, whereas the crusher claw is almost entirely 0:12:38.960 --> 0:12:43.200 or not almost, I think is entirely a slow muscle fiber. 0:12:43.280 --> 0:12:46.640 So it closes more slowly but can close with incredible force. 0:12:47.080 --> 0:12:49.880 And as a result, cutter snaps fast and sharp. Crusher 0:12:49.880 --> 0:12:54.480 closes slowly, but but it's massive. So you could compare 0:12:54.520 --> 0:12:58.120 this to handedness in humans. But Govind notes that while 0:12:58.160 --> 0:13:01.600 the majority of humans are right hand ended, the distribution 0:13:01.640 --> 0:13:05.920 of claws on adult lobsters seems equally probable both ways. 0:13:06.000 --> 0:13:08.120 It's not like the crusher claw is always on the 0:13:08.200 --> 0:13:11.360 left side. It's it's a coin flip, which which would 0:13:11.440 --> 0:13:15.360 mean that there's that natural selection is not pushing it 0:13:15.480 --> 0:13:17.559 one way or the other. Right, it's not, I mean 0:13:17.559 --> 0:13:20.480 it's pushing. It's clearly pushing. The lobsters to have two 0:13:20.559 --> 0:13:23.600 different types of clause for the asymmetry to exist, but 0:13:23.679 --> 0:13:27.240 it doesn't seem to matter which side is which, at 0:13:27.280 --> 0:13:29.880 least not in a way that's universal across lobsters. It 0:13:29.920 --> 0:13:34.520 is decided, It is decided by each individual lobster in development. 0:13:34.640 --> 0:13:37.600 So a great question then, is, okay, if the bilateral 0:13:37.640 --> 0:13:41.040 asymmetry is individual to each lobster and it's a random 0:13:41.080 --> 0:13:44.239 coin flip at least from a you know, uh, statistical 0:13:44.240 --> 0:13:46.880 point of view, what causes the change? How does the 0:13:47.200 --> 0:13:52.880 individual lobster's body when it's growing pick which side becomes which. Well, 0:13:52.920 --> 0:13:56.440 we can look at a lobster larval development to see this. 0:13:56.520 --> 0:13:58.960 So when they're they're tiny little things swimming around before 0:13:59.000 --> 0:14:02.240 they become the big ubsters we recognize. During the early 0:14:02.360 --> 0:14:05.760 larval stages, the claws of the lobster are undifferentiated. They're 0:14:05.760 --> 0:14:10.040 exactly the same. Both claws have what Govin calls quote 0:14:10.080 --> 0:14:13.920 a central band of fast fibers sand which dorsally and 0:14:14.040 --> 0:14:19.000 ventrally by slow fibers. Then during the later juvenile stages, 0:14:19.080 --> 0:14:21.840 this would be like the fourth and fifth molting stages, 0:14:22.200 --> 0:14:25.120 there begins to be some variability in the amount of 0:14:25.200 --> 0:14:28.120 slow and fast fibers in each claw, but then the 0:14:28.200 --> 0:14:31.880 changes really start to become apparent during the sixth stage 0:14:31.880 --> 0:14:36.080 of molting, quote, when the putative crusher claw becomes slightly 0:14:36.160 --> 0:14:39.560 shorter and stouter with a central molar like tooth, while 0:14:39.600 --> 0:14:42.720 the punitive cutter claw remains long and slender with a 0:14:42.840 --> 0:14:47.240 central incisor like tooth. A corresponding asymmetry in the composition 0:14:47.240 --> 0:14:50.080 of the closer muscle also develops. The muscle of the 0:14:50.080 --> 0:14:54.280 cutter claw gradually acquires fast fibers by transforming the slow 0:14:54.360 --> 0:14:57.880 fibers of most of its cross sectional face. The exception 0:14:58.040 --> 0:15:01.320 is a ventral band. The muscle the crusher claw gradually 0:15:01.360 --> 0:15:05.160 transforms all of its fast fibers to slow fibers. In 0:15:05.240 --> 0:15:09.440 succeeding juvenile development. The paired claws further diverge toward well 0:15:09.520 --> 0:15:13.480 defined cutter and crusher claws. So the divergence happens sometime 0:15:13.520 --> 0:15:16.400 in the childhood of a lobster sometime around its fourth 0:15:16.440 --> 0:15:19.720 and fifth molting stages, and really starts to appear during 0:15:19.720 --> 0:15:23.760 the sixth molting. But then Govin mentioned something I thought 0:15:23.840 --> 0:15:26.280 was really intriguing and experiment going all the way back 0:15:26.320 --> 0:15:29.760 to nineteen o eight, way back to a researcher named 0:15:29.880 --> 0:15:33.920 Victor Emmel who found that if you remove one of 0:15:33.920 --> 0:15:36.800 the lobster's claws during the fourth or fifth stage, so 0:15:36.840 --> 0:15:39.560 you just pull that claw off, the claw that is 0:15:39.640 --> 0:15:44.160 left behind, still attached to the lobster, always becomes a 0:15:44.200 --> 0:15:48.160 crusher claw. And meanwhile, the animal regenerates a new claw 0:15:48.240 --> 0:15:50.560 where the old one was torn off. A lot of 0:15:50.600 --> 0:15:53.400 crustaceans can do that. It grows a new claw, and 0:15:53.480 --> 0:15:57.760 the new claw always becomes the cutter claw. But this 0:15:57.840 --> 0:16:00.200 only happens if you do it early. So if you 0:16:00.240 --> 0:16:03.080 pull off a lobster's claw after the larval stage, when 0:16:03.120 --> 0:16:06.440 it's already approaching adulthood, when the asymmetry is already beginning 0:16:06.480 --> 0:16:10.440 to show up, the original arrangement stays intact. The claw 0:16:10.520 --> 0:16:14.200 you pulled off will regenerate as whichever type it already was. 0:16:18.680 --> 0:16:22.640 Thank thank so this this seems to show that claw 0:16:22.760 --> 0:16:26.560 laterality is determined sometime during the molting stages of like 0:16:26.640 --> 0:16:29.760 four to five, and it probably won't change after that. 0:16:30.240 --> 0:16:34.080 So what causes asymmetry to become fixed during this stage 0:16:34.080 --> 0:16:38.000 in a young lobster's life? And here begins a long, 0:16:38.400 --> 0:16:42.320 twisting and to my mind fascinating journey of experiments. Trying 0:16:42.360 --> 0:16:45.880 to pin down how this happens. Most of most of 0:16:45.920 --> 0:16:49.160 these experiments, Govind himself was in some way directly involved in, 0:16:49.720 --> 0:16:52.160 and for the sake of brevity, I'm gonna gloss over 0:16:52.200 --> 0:16:54.600 some details in this section, but you can look up 0:16:54.600 --> 0:16:56.880 the article for yourself if you want. The more zoomed 0:16:56.920 --> 0:17:00.520 inversion with all the details and citations all try to 0:17:00.560 --> 0:17:03.600 give a more sky sky level view. So first of all, 0:17:03.640 --> 0:17:06.560 Govin and colleagues notice some things we already know leading 0:17:06.560 --> 0:17:10.440 into these experiments. One is that the triggers for developing 0:17:10.520 --> 0:17:16.320 different claws must be randomly distributed under normal conditions to 0:17:16.440 --> 0:17:19.600 explain the random distribution of claws in the wild, but 0:17:20.119 --> 0:17:24.160 not random once a claw is lost, and this naturally 0:17:24.200 --> 0:17:28.200 suggested something about use the way the claw is used. 0:17:28.240 --> 0:17:30.720 When one claw is pulled off and has to grow 0:17:30.760 --> 0:17:34.600 back a new it isn't getting used, so the remaining 0:17:34.640 --> 0:17:38.520 claw is getting used, And maybe it's something about getting 0:17:38.640 --> 0:17:42.679 used more that makes a claw into a crusher. This 0:17:42.720 --> 0:17:45.199 would align with the fact that the juvenile stage in 0:17:45.200 --> 0:17:49.400 which the claws become asymmetrical also coincides with a change 0:17:49.440 --> 0:17:51.919 in the lobster's lifestyle. So when the claws start to 0:17:51.920 --> 0:17:55.760 become asymmetrical is around the time when lobsters transition from 0:17:55.840 --> 0:17:59.959 swimming amongst the plankton to living on the ocean floor 0:18:00.119 --> 0:18:03.719 and crawling around on the substrate and burrowing in the substrate. 0:18:04.760 --> 0:18:08.320 The substrate meaning the stuff that lines the ocean floor. Now, 0:18:08.440 --> 0:18:11.359 some research had been done which found that if you 0:18:11.400 --> 0:18:13.639 take a bunch of lobsters and you raise them in 0:18:13.880 --> 0:18:18.680 smooth plastic trays environments with no stuff to mess with 0:18:19.119 --> 0:18:22.399 on the bottom of the water, lobsters do not, in 0:18:22.440 --> 0:18:27.080 fact develop crusher claws at all. In smooth environments, they 0:18:27.160 --> 0:18:31.440 just get symmetrically paired cutter claws, two cutters exactly the same. 0:18:32.119 --> 0:18:34.800 But if you put a lobster that's already reached the 0:18:34.840 --> 0:18:38.240 stage where it's claws split into different types into a 0:18:38.440 --> 0:18:41.679 smooth environment, it keeps its crusher claws. So again it 0:18:41.720 --> 0:18:44.840 gets fixed sometime early on. Alright, So it seems like 0:18:44.840 --> 0:18:47.600 it's the environment that is key here, right, It seems 0:18:47.600 --> 0:18:50.480 to be something about the texture of the environment at 0:18:50.480 --> 0:18:54.400 the right stage that causes crusher claws to emerge. So 0:18:54.560 --> 0:18:57.880 here's a new experiment. You raise lobsters in a smooth 0:18:57.920 --> 0:19:02.600 plastic environment versus one scattered with pieces of broken oyster shells. 0:19:02.880 --> 0:19:06.280 Does a lobster grow up differently with different distributions of 0:19:06.280 --> 0:19:09.879 claws on on smooth plastic versus oyster chips? And the 0:19:09.920 --> 0:19:14.040 results Where oyster shells give you normal asymmetrical lobsters with 0:19:14.080 --> 0:19:18.080 a crusher and a cutter, the smooth no substrate gives 0:19:18.080 --> 0:19:22.760 you a pair of identical cutters. This was fascinating to me. Okay, 0:19:22.800 --> 0:19:26.960 so it's like what it's crawling around on determines how 0:19:27.000 --> 0:19:30.800 its claws develop. So they wanted to refine this answer further. 0:19:30.960 --> 0:19:34.320 Why is this is it? Is this result something about 0:19:34.320 --> 0:19:37.680 oyster chips in particular, or could it be any substrate? 0:19:38.119 --> 0:19:41.440 So they tried the experiment again, but instead of oyster shells, 0:19:41.440 --> 0:19:44.919 they use different stuff. They used gravel, they used mud 0:19:44.920 --> 0:19:50.280 with debris, and they even used tanks with plastic shirt buttons, 0:19:50.320 --> 0:19:53.800 and all of these produced normal lobsters with one crusher, 0:19:53.840 --> 0:19:58.359 one cutter normally randomly distributed crusher claws. And in a 0:19:58.440 --> 0:20:02.000 control they had a flat, smooth substrate that had been 0:20:02.080 --> 0:20:06.200 painted to look like oyster chips, but it did not 0:20:06.600 --> 0:20:09.000 but did not have any actual stuff to crawl or 0:20:09.000 --> 0:20:12.679 burrow around in. And this did not facilitate differentiation. So 0:20:12.760 --> 0:20:15.600 on the one that was flat and smooth but painted, uh, 0:20:15.640 --> 0:20:20.440 it's still produced identical symmetrical cutters. Another experiment to refine 0:20:20.480 --> 0:20:23.879 this what about lobsters and smooth plastic trays, but putting 0:20:23.920 --> 0:20:27.720 them together instead of by themselves. This plays on the 0:20:27.720 --> 0:20:30.080 fact that lobsters are not very friendly to each other. 0:20:30.200 --> 0:20:33.720 They are aggressive and tend to fight each other, and 0:20:33.760 --> 0:20:36.239 typically when they were put in together they would they 0:20:36.240 --> 0:20:38.880 would duel a bit, and one of the lobsters would 0:20:38.920 --> 0:20:42.720 often get one or both claws removed in battle. Yeah, 0:20:42.760 --> 0:20:44.600 I know this is kind of going into bug fights 0:20:44.680 --> 0:20:47.919 territory um, but the lobster. So what they found was 0:20:47.960 --> 0:20:50.919 the lobster with both claws left would split like in 0:20:50.960 --> 0:20:54.600 the wild with an asymmetrical distribution with one crusher claw. 0:20:55.000 --> 0:20:57.520 So if there is no substrate, if you don't have 0:20:57.560 --> 0:21:00.520 any mud or oyster chips to root around in fighting, 0:21:00.560 --> 0:21:04.760 will also do to split your claws into different types. Okay, 0:21:04.760 --> 0:21:07.480 that this makes sense. It's about having It would seem 0:21:07.520 --> 0:21:09.440 to have something to do with the the sorts of 0:21:09.840 --> 0:21:14.080 things you're encountering with your claws, be it chunks of 0:21:14.080 --> 0:21:18.800 oysters or the hard body of another lobster combatant, Right, 0:21:18.880 --> 0:21:21.240 it seems to have something to do with doing something 0:21:21.320 --> 0:21:25.240 with the claws that that produces one crusher of the two. 0:21:25.800 --> 0:21:28.000 Oh and as a control, I thought this is also interesting. 0:21:28.000 --> 0:21:29.439 They're like, well, we want to make sure it's not 0:21:29.520 --> 0:21:32.880 just the appearance of another lobster that causes a crusher 0:21:32.920 --> 0:21:35.840 to develop. So they tried one with a smooth container 0:21:35.880 --> 0:21:39.520 but a mirror, So if the lobster could see its reflection, 0:21:39.560 --> 0:21:42.000 would this make it differentiate? But noe, period, you just 0:21:42.080 --> 0:21:45.840 got two cutters. It's got to be that tactile experience. Okay, yeah, 0:21:46.400 --> 0:21:48.240 so so far this is all lining up with the 0:21:48.320 --> 0:21:52.280 hypothesis that it's something about the claw getting used more 0:21:52.400 --> 0:21:55.760 that caused them to split and one to become a crusher. Uh. 0:21:55.840 --> 0:21:58.399 So they tried a new experiment with the hypothesis that 0:21:58.440 --> 0:22:00.760 if you put a lobster in a no normal environment 0:22:00.760 --> 0:22:04.399 with a substrate, but you prevent only one of a 0:22:04.440 --> 0:22:07.720 lobster's clause from opening and closing, that's going to get 0:22:07.760 --> 0:22:10.200 less use. That's going to turn into the cutter claw, 0:22:10.280 --> 0:22:13.639 and the other one will become a crusher. Okay, So 0:22:13.680 --> 0:22:16.680 they tried this with various methods such as holding one 0:22:16.720 --> 0:22:19.040 claw shut with a rubber band or with a dab 0:22:19.080 --> 0:22:22.960 of glue, and they found, to their surprise, this did 0:22:23.040 --> 0:22:26.119 not produce the result they expected. They thought, if a 0:22:26.160 --> 0:22:28.840 claw can't open and close, that the other one is 0:22:28.840 --> 0:22:31.480 going to become the crusher. But no, Instead, with these lobsters, 0:22:31.760 --> 0:22:34.960 you still got random lateralization. In some the right became 0:22:35.000 --> 0:22:37.520 a crusher and some of the left became a crusher. Wow, 0:22:37.760 --> 0:22:40.520 so it's it because that was gonna be my guest 0:22:40.560 --> 0:22:43.080 that it depends on how on how that particular claw 0:22:43.240 --> 0:22:47.159 is being used. But we see this, uh, this this 0:22:47.320 --> 0:22:51.160 random distribution occurring even when that one claw is say, 0:22:51.359 --> 0:22:55.400 rubber bandage shut. Right. So here they were like, well, 0:22:55.400 --> 0:22:57.639 maybe has something to do with the claw being used, 0:22:57.680 --> 0:23:00.600 but not with it being able to open clothes, and 0:23:00.680 --> 0:23:04.000 maybe it's something else. So from here they proceeded to 0:23:04.080 --> 0:23:07.200 a number of different anatomical experiments and to try to 0:23:07.280 --> 0:23:10.320 quickly summarize their findings. First of all, they found if 0:23:10.320 --> 0:23:13.240 you caught a tendon preventing only one of a lobster's 0:23:13.240 --> 0:23:16.480