WEBVTT - Life in the Hypogean World, Part 2 0:00:03.040 --> 0:00:06.800 Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. 0:00:12.600 --> 0:00:14.920 Hey, Welcome to Stuff to Blow Your Mind. My name 0:00:14.960 --> 0:00:15.560 is Robert. 0:00:15.400 --> 0:00:18.600 Lamb and I am Joe McCormick. And Hey, we are 0:00:18.640 --> 0:00:22.680 back with part two of our series on cave ecosystems 0:00:22.760 --> 0:00:28.120 and hypogean biology cave biology. In the last episode, we 0:00:28.280 --> 0:00:32.280 talked about some of the characteristic features of cave ecosystems, 0:00:32.600 --> 0:00:36.880 and then we ended up discussing how lightless cave environments 0:00:37.000 --> 0:00:42.280 shaped the evolution of a creature called Astianax Mexicanus, or 0:00:42.320 --> 0:00:46.320 the blind Mexican cavefish, also known as the Mexican tetra, 0:00:47.159 --> 0:00:51.520 of which many populations have adapted to life in subterranean 0:00:51.600 --> 0:00:57.200 waterways by losing their eyes and the pigments in their flesh. 0:00:57.240 --> 0:00:59.080 We ended up kind of doing a deep dive on 0:00:59.120 --> 0:01:02.600 the evolution mary logic of this why an animal population 0:01:03.160 --> 0:01:07.240 that once had eyes and skin pigment would adapt over 0:01:07.319 --> 0:01:11.000 many generations to lose those traits in a cave. So 0:01:11.120 --> 0:01:13.320 if you haven't heard part one yet, you should probably 0:01:13.319 --> 0:01:15.240 go back and check that one out first. But we 0:01:15.280 --> 0:01:17.840 are back again today to talk about some more elements 0:01:17.840 --> 0:01:21.120 of cave biology, specifically One of the things I wanted 0:01:21.160 --> 0:01:24.160 to get into we didn't really have time for last time, 0:01:24.280 --> 0:01:28.120 was something else about blind Mexican cavefish, which is, if 0:01:28.160 --> 0:01:31.520 they have no site, what do they do? How do 0:01:31.600 --> 0:01:34.319 they navigate their environment and forage for food? 0:01:35.040 --> 0:01:37.800 And this is key because they've got to eat something. 0:01:37.880 --> 0:01:41.280 And these are extreme environments that are generally regarded as 0:01:41.319 --> 0:01:45.600 not being the most bountiful places to scrape out a 0:01:45.680 --> 0:01:47.280 livelihood as an organism. 0:01:47.640 --> 0:01:50.600 Right, And there might be some advantages to living in 0:01:50.640 --> 0:01:52.600 a cave if you are a fish like this, Like 0:01:52.640 --> 0:01:56.120 there might be fewer predators than you would encounter in 0:01:56.200 --> 0:01:59.400 the world above, but there are also fewer food resources, 0:02:00.480 --> 0:02:02.920 so you know you have to you have to kind 0:02:02.960 --> 0:02:04.640 of like shift your specialization. 0:02:05.360 --> 0:02:08.200 Yeah, Like, if I was to decide, again, this is 0:02:08.280 --> 0:02:11.079 a non evolutionary example, but if I was to decide 0:02:11.120 --> 0:02:14.440 I am going to now live in my local Ikea store, well, 0:02:14.800 --> 0:02:17.480 you know, I've got to figure out some new things. Right, 0:02:17.480 --> 0:02:19.040 It's going to be easy to find a bed when 0:02:19.440 --> 0:02:21.280 the lights go out, but I'm gonna have to deal 0:02:21.320 --> 0:02:24.800 with the night security. My diet is going to consist 0:02:24.960 --> 0:02:26.480 entirely of Ikea food. 0:02:26.960 --> 0:02:28.200 So if you like Lingenberry. 0:02:29.240 --> 0:02:32.079 Yeah, yeah, make sure you don't have a Linenberry allergy 0:02:32.520 --> 0:02:33.000 for sure. 0:02:33.639 --> 0:02:36.280 Yeah. So I wanted to explore this question of how 0:02:36.400 --> 0:02:40.720 do blind cavefish since their surroundings, and so I was 0:02:40.760 --> 0:02:44.200 looking into this and I discovered that apparently one major 0:02:44.440 --> 0:02:47.639 sense mechanism that they rely on is what's known as 0:02:47.680 --> 0:02:52.480 the lateral line system. And this is not a sense 0:02:52.600 --> 0:02:56.200 that is unique to blind cavefish. The lateral line system 0:02:56.680 --> 0:02:59.720 is found in lots of aquatic vertebrates, even those that 0:02:59.800 --> 0:03:03.160 can and see. Though in blind fish there are usually 0:03:03.400 --> 0:03:06.079 enhancements to this system, so it's a sense that they 0:03:06.200 --> 0:03:11.040 already have, but it gets stronger in the cave evolved variants. 0:03:11.560 --> 0:03:15.720 As a side note, I always really enjoy imagining types 0:03:15.760 --> 0:03:18.959 of senses that humans don't have, like what it would 0:03:19.000 --> 0:03:21.200 be like to have a different kind of sense, you know, 0:03:21.240 --> 0:03:25.880 like electro reception or magnetic perception or something like that. 0:03:26.600 --> 0:03:31.239 And this sense in particular, I'm very excited to try 0:03:31.240 --> 0:03:34.680 to imagine because it's very spooky trying to imagine it. 0:03:34.680 --> 0:03:38.280 It's something about it feels almost kind of halloweeny. This 0:03:38.360 --> 0:03:40.640 might make more sense once I explain it. So, the 0:03:40.680 --> 0:03:45.200 basic function of the lateral line system is to detect 0:03:45.440 --> 0:03:51.240 movements in the water surrounding the animal through high sensitivity 0:03:51.320 --> 0:03:56.200 to changes in water pressure. This system it runs along 0:03:56.280 --> 0:03:58.520 the length of an animal like a fish, so there'll 0:03:58.560 --> 0:04:02.960 be sort of nals of the lateral line sensing organs 0:04:03.080 --> 0:04:06.680 around the head of the fish and then running lengthwise 0:04:06.720 --> 0:04:11.960 along the body. The system uses sensory organs known as 0:04:12.200 --> 0:04:17.280 neuro masts, which contain little hairs suspended within a kind 0:04:17.320 --> 0:04:22.800 of jelly filled capsule that bends in response to changes 0:04:22.839 --> 0:04:26.480 in water pressure and flow. And then these little hairs 0:04:26.560 --> 0:04:30.200 are connected to nerve cells that are strung along the 0:04:30.279 --> 0:04:35.320 lateral line system like Christmas tree lights. Sometimes the neuromasts 0:04:35.400 --> 0:04:38.400 are exposed to the water on the outside of the skin. 0:04:38.440 --> 0:04:40.279 They're just right on the outside of the skin, but 0:04:40.520 --> 0:04:44.360 other times they are contained within a kind of duct 0:04:44.640 --> 0:04:48.279 or canal that is just under the surface of the skin. 0:04:49.120 --> 0:04:51.880 And either way that the purpose of the lateral line 0:04:51.880 --> 0:04:58.120 system is to detect vibrations, movements, and objects within the 0:04:58.160 --> 0:05:03.120 water by sensing the little changes in water pressure and flow. 0:05:03.279 --> 0:05:06.920 So with this system, an animal can get feedback about 0:05:06.920 --> 0:05:09.479 its own movement through the water, for one thing, but 0:05:09.560 --> 0:05:13.880 it can also sense the presence of currents and nearby 0:05:14.120 --> 0:05:18.320 solid masses, either moving or stationary, by the way they 0:05:18.360 --> 0:05:23.440 displace water as the fish moves through it. And this 0:05:23.520 --> 0:05:25.040 is coming back to what I was saying a minute ago, 0:05:25.480 --> 0:05:28.520 something about trying to imagine this is. Oh, it's very 0:05:28.560 --> 0:05:31.640 evocative and a little bit scary, almost so imagining living 0:05:32.240 --> 0:05:34.839 in a place of dark water. But you can sense 0:05:35.080 --> 0:05:38.440 objects around you by the way they move the water, 0:05:38.560 --> 0:05:40.839 or by the way they change how the water moves 0:05:40.880 --> 0:05:41.400 around you. 0:05:42.400 --> 0:05:44.200 Oh wow, I mean, we're getting right back into that 0:05:44.279 --> 0:05:49.280 Gollumn territory, you know. I'm imagining Gollum sensing that goblin 0:05:49.320 --> 0:05:51.880 that has come down and is washing its hands in 0:05:51.920 --> 0:05:56.040 the water, and so forth on this lightless underground lake. 0:05:56.640 --> 0:05:58.800 And to your point, it is so alien to try 0:05:58.839 --> 0:06:01.520 and imagine this. I'm in the water a fair amount. 0:06:01.560 --> 0:06:04.960 I swim laps most mornings. They'll swim in this morning, 0:06:05.480 --> 0:06:09.080 and it's still you know, it's a very visual exercise. 0:06:09.160 --> 0:06:11.640 You can send You can feel things in the water, 0:06:11.720 --> 0:06:14.839 obviously you can. And Lord knows, there's a lot to 0:06:14.880 --> 0:06:18.280 see and feel in a Ymca pool. You know, there 0:06:18.279 --> 0:06:22.000 are people doing exercise classes, there are people swimming laps 0:06:22.040 --> 0:06:24.960 next to you, sometimes very often in the same lane 0:06:25.000 --> 0:06:27.800 with you, and you pick up on those movements, but 0:06:28.160 --> 0:06:32.240 nowhere near this level of detail. You know, this is 0:06:32.320 --> 0:06:34.560 like compared to what we have. This is like a 0:06:34.600 --> 0:06:35.480 second site. 0:06:35.960 --> 0:06:38.680 Yeah, I kind of ghostly vision through which you can 0:06:38.800 --> 0:06:40.880 you can sense things around you by the way they 0:06:40.920 --> 0:06:42.680 move the water against your body. 0:06:43.720 --> 0:06:44.440 Yeah. 0:06:44.520 --> 0:06:48.799 So anyway, the astyanax fish, the Mexican blind cavefish, apparently 0:06:48.839 --> 0:06:51.880 compensate for their lack of vision by having a more 0:06:52.000 --> 0:06:56.280 sensitive lateral line system than their surface dwelling cousins, and 0:06:56.360 --> 0:07:00.600 this helps them navigate, forage and survive in their lightless environment. 0:07:01.640 --> 0:07:06.159 But this way of living depends not just on heightened 0:07:06.160 --> 0:07:10.320 sensitivity to water displacement, but also on changes to behavior. 0:07:11.440 --> 0:07:14.360 For example, one thing I was reading about is that 0:07:14.720 --> 0:07:19.800 when preparing to mate, apparently male and female blind cavefish 0:07:20.520 --> 0:07:25.680 engage in this in these patterns of exaggerated movements of 0:07:25.760 --> 0:07:29.480 various body parts like the mouth and the gills, and 0:07:29.600 --> 0:07:33.800 these movements are thought to perhaps help the mating partners 0:07:34.040 --> 0:07:38.120 find and identify one another without visual cues. Does that 0:07:38.120 --> 0:07:40.480 make sense, like moving around in the water more so 0:07:40.520 --> 0:07:44.040 that they can locate one another of course, the fish 0:07:44.080 --> 0:07:46.760 also have changes to their metabolism to allow them to 0:07:46.800 --> 0:07:49.040 survive in a place where food is less abundant than 0:07:49.080 --> 0:07:52.200 it is on the surface, so they are thought to 0:07:52.280 --> 0:07:56.559 have slower metabolisms to need less food energy. But also 0:07:56.720 --> 0:08:00.120 I was reading about an interesting twenty seventeen study published 0:08:00.160 --> 0:08:04.440 in Plus one by some researchers associated with the University 0:08:04.440 --> 0:08:08.080 of Cincinnati, and this was on the role of a 0:08:08.640 --> 0:08:13.640 symmetry in blind cavefish evolution. We actually did a whole 0:08:13.680 --> 0:08:16.280 series on asymmetry and animals a while back in which 0:08:16.280 --> 0:08:19.440 we talked about fiddler crabs and such, fiddler crabs having 0:08:19.600 --> 0:08:22.760 one claw much much bigger than the other. But we 0:08:22.800 --> 0:08:24.800 talked about a lot of examples in the animal world, 0:08:24.880 --> 0:08:27.040 and I remember that being a very interesting series. 0:08:27.440 --> 0:08:29.320 Yeah, that was a fun one for sure, you know, 0:08:29.360 --> 0:08:32.440 with some of the outrageous examples in some of the 0:08:32.640 --> 0:08:36.599 less obvious examples of asymmetry. 0:08:36.760 --> 0:08:39.600 Apparently there is a bit of hidden asymmetry in the 0:08:39.640 --> 0:08:43.240 blind Mexican cavefish as well, So let's see. This study 0:08:43.360 --> 0:08:46.800 was by Amandicate Powers, aeronam Davis, Shane A. Kaplan, and 0:08:46.880 --> 0:08:50.640 Joshua be Gross, published in Plus one in twenty seventeen, 0:08:50.679 --> 0:08:54.120 and it was called cranial asymmetry arises later in the 0:08:54.200 --> 0:08:58.800 life history of the blind Mexican cavefish a Stianax Mexicanus. 0:08:59.080 --> 0:09:01.480 And so we were talking in the previous episode about 0:09:01.480 --> 0:09:04.640 how in some of these cavefish populations, the fish are 0:09:04.720 --> 0:09:08.520 not without eyes from the very beginning. Rather, they do 0:09:08.960 --> 0:09:13.320 grow eyes initially in embryonic development, but then the eyes 0:09:13.360 --> 0:09:17.440 go through what's called regression where they are absorbed and 0:09:17.600 --> 0:09:21.240 disappear as the fish grows, and then the bone around 0:09:21.240 --> 0:09:24.240 the eye socket collapses in by the time the fish 0:09:24.320 --> 0:09:29.400 is an adult. Young cavefish apparently start life with fairly 0:09:29.720 --> 0:09:33.560 symmetrical bodies, and the surface variants in the rivers above 0:09:33.600 --> 0:09:37.120 where there's plenty of light also have fairly symmetrical bodies 0:09:37.160 --> 0:09:40.959 even as adults. But the young cavefish start out fairly symmetrical, 0:09:41.920 --> 0:09:45.719 and then as they mature a mismatch develops in how 0:09:45.760 --> 0:09:48.720 the bones on either side of their skull take shape. 0:09:49.320 --> 0:09:52.520 And this asymmetry in their cranial bones seems to match 0:09:52.559 --> 0:09:55.520 a difference in behavior between the cave variant of the 0:09:55.520 --> 0:09:58.840 tetras and the surface variant still has eyes. The surface 0:09:58.920 --> 0:10:02.360 variant when you place it in a fish tank, will 0:10:02.559 --> 0:10:05.480 swim in more random patterns or will just kind of 0:10:05.520 --> 0:10:08.559 float without moving in the shaded portions of the tank. 0:10:09.360 --> 0:10:12.720 The cave variant, on the other hand, will just keep 0:10:13.040 --> 0:10:16.720 it'll keep swimming in circles around the edges of its tank, 0:10:17.400 --> 0:10:20.800 and this matches with the fact that has been observed 0:10:20.800 --> 0:10:25.120 in the wild. In its natural environment, the cave variant 0:10:25.200 --> 0:10:28.480 will tend to follow the rocky walls of the pool 0:10:28.520 --> 0:10:33.400 where it lives, swimming counterclockwise around these boundaries in an 0:10:33.520 --> 0:10:38.040 endless loop. And one of the studies authors, Amanda Powers, 0:10:38.120 --> 0:10:41.800 was quoted in a press release about the research, explaining, quote, 0:10:42.480 --> 0:10:45.760 you could see how asymmetry might be an advantage in navigation. 0:10:46.320 --> 0:10:50.120 They tend to swim in a unidirectional circular motion around 0:10:50.160 --> 0:10:54.520 their tanks to explore their surroundings. Having asymmetry in their skull, 0:10:54.600 --> 0:10:57.880 we think is attributed to handedness. If their skull is 0:10:57.960 --> 0:11:01.320 bent to the left, they could be right handed. They're 0:11:01.400 --> 0:11:04.800 feeling the wall to the right with their sensory structures. 0:11:05.800 --> 0:11:08.680 Oh wow, yeah, So it seems that the cavefish have 0:11:08.720 --> 0:11:13.800 a type of developmental handedness that correlates to a navigation 0:11:14.000 --> 0:11:18.520 behavior where they follow the walls of their natural enclosure 0:11:18.960 --> 0:11:24.079 in this slow, counterclockwise lapping motion. Though I think it's 0:11:24.080 --> 0:11:27.400 still not fully understood how this system emerges, if it 0:11:27.480 --> 0:11:31.360 helps them survive how, we don't fully know yet, but 0:11:31.400 --> 0:11:36.640 it's interesting to imagine why. Another interesting sort of unrelated 0:11:36.679 --> 0:11:38.800 thing that I was just reading in this press release, 0:11:39.480 --> 0:11:42.200 also quoting the same author of the paper, I mean, 0:11:42.360 --> 0:11:45.040 powers talking about how she and colleagues went into the 0:11:45.080 --> 0:11:48.200 caves to observe these fish, and she says in this 0:11:48.320 --> 0:11:51.520 article quote, whenever you would touch the surface of the 0:11:51.559 --> 0:11:54.559 water with your finger, a swarm of cavefish would come 0:11:54.679 --> 0:11:57.280 right up to it. Not many fish would do that. 0:11:57.480 --> 0:12:00.840 These cavefish have zero predators, are not afraid. 0:12:01.480 --> 0:12:04.080 Oh wow, that you know. That reminds me of other 0:12:04.080 --> 0:12:07.240 examples we've talked about in the show, like various birds 0:12:07.240 --> 0:12:11.320 of the Galapagos Islands, for example. It reminds me of 0:12:11.360 --> 0:12:13.800 some stuff I was just reading the other day about 0:12:13.840 --> 0:12:17.640 the dodo bird. You know, where you have these organisms 0:12:17.679 --> 0:12:22.640 that adapt over evolutionary time to an environment where there 0:12:22.640 --> 0:12:25.319 are no predators or there is just an entirely different 0:12:25.559 --> 0:12:30.839 predation situation going on, And yeah, they just lose their fear. 0:12:31.160 --> 0:12:34.600 There's no need to engage in that kind of protective 0:12:34.640 --> 0:12:38.520 behavior because those things don't exist for them until they 0:12:38.520 --> 0:12:41.480 show up on a bub Yeah yeah, speaking. 0:12:41.200 --> 0:12:44.800 Dutch, Okay, So that's lateral line sensations, and then the 0:12:45.240 --> 0:12:48.439 asymmetry of the skull, the kind of the circling behavior, 0:12:48.840 --> 0:12:51.040 all those differences. But there was one more thing I 0:12:51.040 --> 0:12:54.320 wanted to talk about. I mentioned in the previous episode 0:12:55.480 --> 0:12:59.320 another sensory enhancement found in some of these cavefish, and 0:12:59.320 --> 0:13:03.800 that sensory enhancement was taste. It appeared to be involved 0:13:03.920 --> 0:13:09.160 in a plyotropy. Remember that's where a single genetic change 0:13:09.200 --> 0:13:13.160 would result in multiple different changes in the phenotype in 0:13:13.200 --> 0:13:17.000 the body or the behavior, And in this case, the 0:13:17.800 --> 0:13:20.120 idea was that there was a single genetic change that 0:13:20.120 --> 0:13:23.600 would result in both regression of the eyes. So this 0:13:23.679 --> 0:13:25.520 process we talked about where the eyes are sort of 0:13:25.559 --> 0:13:28.839 absorbed and the adult fish doesn't have eyes, and then 0:13:29.000 --> 0:13:35.160 along with that development of a greater number of taste buds. Now, 0:13:35.520 --> 0:13:38.600 we speculated generally in the last episode that yeah, you know, 0:13:38.679 --> 0:13:41.920 having enhanced other senses in a cave would probably be 0:13:42.000 --> 0:13:44.520 useful in some way. Taste buds are generally useful. They 0:13:44.520 --> 0:13:47.600 are our body's chemistry set to know what we're putting 0:13:47.640 --> 0:13:51.240 in the digestive tract. But I was wondering if there 0:13:51.240 --> 0:13:53.360 was anything else we could know about that, like how 0:13:53.400 --> 0:13:56.640 do these extra taste buds work in these fish? What 0:13:56.720 --> 0:13:59.880 kind of benefit do they provide? So this is another 0:14:00.080 --> 0:14:02.160 thing where the answer is not fully known yet we 0:14:02.240 --> 0:14:06.280 know a few kind of interesting morsels. So I came 0:14:06.320 --> 0:14:09.680 across a very recent paper addressing this question. It was 0:14:09.720 --> 0:14:13.280 by Daniel Burning and Joshua B. Gross published in Frontiers 0:14:13.280 --> 0:14:16.679 and Ecology and Evolution twenty twenty three, called the Constructive 0:14:16.679 --> 0:14:21.760 Evolution of Taste in astianax Cavefish. A review and one 0:14:21.760 --> 0:14:23.720 of the things I thought was interesting here, Rob, I've 0:14:23.760 --> 0:14:27.120 attached a I've attached a diagram for you to look at. 0:14:27.400 --> 0:14:31.400 It seems that mostly what we're talking about are what's 0:14:31.400 --> 0:14:36.160 called extra oral taste buds, taste buds that are not 0:14:36.520 --> 0:14:40.640 inside the mouth like ours, but outside the mouth and 0:14:40.720 --> 0:14:43.640 spread out over the jaws in the front of the face. 0:14:44.360 --> 0:14:48.120 So in this diagram it shows blind cavefish from a 0:14:48.120 --> 0:14:52.840 couple of different populations compared to the surface variant with 0:14:53.000 --> 0:14:56.440 taste buds filled in as red dots on the illustrations, 0:14:56.880 --> 0:14:59.680 and while the surface variant looks like it is wearing 0:14:59.760 --> 0:15:02.400 lip stick, you know, the red dots, the taste buds 0:15:02.400 --> 0:15:05.840 are on the mouth, the cave fish are wearing clown makeup. 0:15:06.080 --> 0:15:08.120 The taste buds are all over the face. 0:15:08.720 --> 0:15:12.680 Yeah, it's quite impressive. And again it makes sense for 0:15:12.760 --> 0:15:15.440 this kind of an environment, you know, you need to 0:15:15.560 --> 0:15:20.080 lean into a different sense situation. It reminds me a 0:15:20.080 --> 0:15:23.760 bit of our past discussions about catfish being super tasters, 0:15:23.800 --> 0:15:27.160 you know, and really when and again it come back 0:15:27.160 --> 0:15:30.200 to that situation where we have our human understanding of 0:15:30.560 --> 0:15:34.960 the senses, but we have a human level understanding of 0:15:34.960 --> 0:15:37.480 those senses. And so when you're talking about something like 0:15:37.560 --> 0:15:42.000 this that is enhanced, it's it's not taste as we 0:15:42.120 --> 0:15:43.640 know it, it's something different. 0:15:44.400 --> 0:15:47.240 Yeah, exactly. So I was wondering, like, what do we 0:15:47.360 --> 0:15:50.160 know about what kind of difference this makes? What difference 0:15:50.200 --> 0:15:53.200 does it make in the lives of these fish. So 0:15:53.240 --> 0:15:55.760 there are a few things mentioned in this review. One 0:15:55.840 --> 0:15:59.440 is that multiple studies have found what appears to be 0:15:59.720 --> 0:16:05.160 in enhanced sensitivity to chemical repellence and taste sources in 0:16:05.200 --> 0:16:09.040 the water in the cavefish when compared to the surface fish. 0:16:09.120 --> 0:16:13.000 So just one example is a study by Humbach in 0:16:13.120 --> 0:16:17.840 nineteen sixty that found in the cave fish compared to 0:16:18.240 --> 0:16:23.320 the common minno, that the modality for bitter sensation was 0:16:23.640 --> 0:16:27.960 three hundred times more acute roughly, and then the salty 0:16:28.040 --> 0:16:33.200 slash acid slash sweet modality difference was about two thousand 0:16:33.280 --> 0:16:36.200 to four thousand times more acute in the cavefish. So 0:16:36.760 --> 0:16:41.920 much greater, much lower. I guess threshold of sensitivity to 0:16:42.040 --> 0:16:45.280 these tastes also protus at all. In two thousand and 0:16:45.280 --> 0:16:49.960 eight found quote amino acids dissolved in system water were 0:16:50.000 --> 0:16:54.480 detected at a much lower concentration in paschone cavefish. That's 0:16:54.960 --> 0:17:00.440 from one particular cave source paschone cavefish compared to surface fish. 0:17:00.480 --> 0:17:04.119 And one possible explanation the authors discuss for this heightened 0:17:04.160 --> 0:17:07.600 sensitivity to amino acids could be what they call the 0:17:07.640 --> 0:17:12.720 savory taste receptor T one R one. This is the 0:17:12.880 --> 0:17:16.919 receptor that binds to glutamate and helps us taste savory 0:17:17.160 --> 0:17:20.800 umami flavors. So I wonder if you could really get 0:17:20.840 --> 0:17:24.480 these cavefish going bananas over. You know, something in the water. 0:17:24.600 --> 0:17:27.399 A piece of food or whatever is dispersed in the 0:17:27.400 --> 0:17:28.879 water if you hit it with a bit of the 0:17:28.920 --> 0:17:30.240 good old MSG. 0:17:31.200 --> 0:17:34.200 I bet, or maybe one of those little fish shaped 0:17:35.160 --> 0:17:37.360 soy soy sauce. 0:17:37.600 --> 0:17:41.240 Yeah, we get some soy sauce, some parmesan cheese, some tomatoes, 0:17:41.359 --> 0:17:45.320 some MSG all the good, all the good savory things. However, 0:17:45.400 --> 0:17:48.400 the authors do say that several amino acids were used 0:17:48.440 --> 0:17:50.080 in the study that found this, so there could be 0:17:50.240 --> 0:17:55.120 other explanations, possibly also involving old faction rather than taste. 0:17:56.160 --> 0:18:00.960 But anyway, what difference would these these taste but arrangements 0:18:00.960 --> 0:18:05.480 and heightened sensitivity to flavors make in terms of the 0:18:05.520 --> 0:18:09.600 behavior of the fish the author's right quote. One recent 0:18:09.600 --> 0:18:13.600 study argued that external taste buds are used for preliminary 0:18:13.760 --> 0:18:18.960 assessment of food items during random swimming or targeted searches 0:18:18.960 --> 0:18:23.280 for food. Extra oral taste buds thus carry in importance 0:18:23.320 --> 0:18:28.199 for determining whether to pursue or avoid a food item. So, 0:18:28.240 --> 0:18:33.240 the way I understand that is it's heightening the fish's 0:18:34.320 --> 0:18:38.160 foraging efficiency basically by saying, before you even get something 0:18:38.240 --> 0:18:41.480 in the mouth, you're tasting the water around this thing 0:18:41.800 --> 0:18:44.800 with the front of your face, and it helps you 0:18:45.160 --> 0:18:47.919 zero in more quickly on something that is good to 0:18:47.960 --> 0:18:49.960 eat or is not good to eat, Like you're getting, 0:18:50.040 --> 0:18:52.760 you're getting an idea about whether you're coming close to 0:18:52.800 --> 0:18:55.439 a good piece of food or not earlier. So that 0:18:55.480 --> 0:18:57.320 would make your foraging more efficient. 0:18:58.119 --> 0:19:00.159 Okay, that makes sense in the And. 0:19:00.280 --> 0:19:03.720 However, they do say that this is just an area 0:19:03.880 --> 0:19:06.679 that hasn't had enough research yet. They say that the 0:19:06.880 --> 0:19:11.080 quote precise function of cavefish extraoral taste buds remains unclear 0:19:11.240 --> 0:19:15.080 and largely unexplored. And then they also say that future 0:19:15.119 --> 0:19:18.520 studies need to do things like excluding the role of 0:19:18.520 --> 0:19:22.760 old faction or smell and isolating the variable of taste. 0:19:23.760 --> 0:19:27.280 And there are differences that even remain that they did 0:19:27.280 --> 0:19:29.160 examine in the paper that we just don't know how 0:19:29.160 --> 0:19:32.800 to explain yet, but could possibly be related to taste. 0:19:33.320 --> 0:19:37.000 One interesting idea they bring up is the feeding angle. 0:19:37.280 --> 0:19:39.680 So they say, you know, if you look at the 0:19:40.680 --> 0:19:45.000 cave variants of these fish versus the surface variants, one 0:19:45.040 --> 0:19:48.000 thing you will notice is that they both go along 0:19:48.119 --> 0:19:51.119 the bottom. There might be like a stony or sandy 0:19:51.160 --> 0:19:53.640 or pebbly bottom of the water source where they are 0:19:54.520 --> 0:19:57.560 and they'll go along the bottom with their mouth down 0:19:57.600 --> 0:19:59.639 to the bottom, kind of searching for little bits of 0:19:59.640 --> 0:20:03.040 food to eat or you know, prey in the case 0:20:03.080 --> 0:20:06.280 of you know, carnivory or just little bits of dead 0:20:06.440 --> 0:20:08.800 organic matter, whatever it is they're coming across to eat. 0:20:09.000 --> 0:20:12.760 They're scouring the bottom for it. For some reason, the 0:20:12.800 --> 0:20:17.760 surface fish have a steeper angle that they forage at 0:20:17.800 --> 0:20:21.640 with their body more it's almost more totally vertical, whereas 0:20:21.680 --> 0:20:25.120 the cavefish tend to forage at a more slanted angle 0:20:25.520 --> 0:20:29.480 that's closer. It's more like fifty five degrees from the 0:20:29.480 --> 0:20:32.840 bottom versus more like eighty degrees in the surface variant. 0:20:33.119 --> 0:20:35.520 They say this could be related to the changes in 0:20:37.119 --> 0:20:40.560 extraoral taste buds. Maybe it's you know, like they're tasting 0:20:40.600 --> 0:20:43.480 things differently, thus they have to orient their bodies differently. 0:20:44.119 --> 0:20:47.000 Don't know, but interesting question. 0:20:47.760 --> 0:20:50.720 Yeah, yeah, I mean this this is fascinating to think about, 0:20:50.800 --> 0:20:53.840 Like it makes one wonder if it has something to 0:20:53.880 --> 0:20:59.680 do with their being more predation opportunities for the surface fish, 0:21:00.240 --> 0:21:02.600 Like you've got to come in at that steeper angle 0:21:02.760 --> 0:21:06.280 because there's a greater risk of things, you know, on 0:21:06.400 --> 0:21:10.600 the floor of the of the sea or what have you, 0:21:11.000 --> 0:21:14.440 that might come after them while they're feeding, and maybe 0:21:14.440 --> 0:21:16.639 those are absent in these cave environments. Again, you know 0:21:16.680 --> 0:21:20.159 we're talking about like a lack of just biodiversity in 0:21:20.200 --> 0:21:23.000 those environments. You know there's many fewer predators, et cetera. 0:21:23.680 --> 0:21:25.720 But who knows. That's just me spitballing. 0:21:26.400 --> 0:21:28.080 I don't want to act like I'm just look at 0:21:28.080 --> 0:21:30.359 a diagram and a paper and answer the question. But 0:21:30.480 --> 0:21:33.199 just one thing I wonder about is looking at the 0:21:33.520 --> 0:21:36.040 looking again at the diagram of where these extra oral 0:21:36.160 --> 0:21:39.440 taste buds are in the surface fish. Remember they're all 0:21:39.480 --> 0:21:42.719 like right at the mouth, but in the in the 0:21:42.760 --> 0:21:45.160 cave variant, a lot of them tend to be spread 0:21:45.160 --> 0:21:49.159 out along the lower jaw. So I wonder if it 0:21:49.240 --> 0:21:52.120 can come in at this shallower angle because it's sort 0:21:52.160 --> 0:21:55.880 of like feeling and tasting more along the bottom without 0:21:55.920 --> 0:21:58.400 having to get the front of its mouth in contact 0:21:58.480 --> 0:22:00.560 with it. It can kind of taste with the the 0:22:00.640 --> 0:22:01.920 slope of its lower jaw. 0:22:02.400 --> 0:22:03.720 Yeah, that would make a lot of sense. 0:22:03.960 --> 0:22:07.920 But yeah, again, don't know. Interesting questions about Usually when 0:22:07.960 --> 0:22:10.200 you think about fish and taste together, you're thinking about 0:22:10.200 --> 0:22:12.400 what a fish tastes like to you not what it's 0:22:12.440 --> 0:22:14.000 like to taste as a fish. 0:22:14.440 --> 0:22:17.480 Yeah, which again it can put you an entirely different 0:22:17.520 --> 0:22:22.400 sense realities, especially considering things like a catfish. But also 0:22:22.520 --> 0:22:26.359 you know, getting into taste and smell. Whenever I read 0:22:26.400 --> 0:22:30.439 information about, you know, the distances at which fish in 0:22:30.480 --> 0:22:34.040 the ocean can detect other things going on, say blood 0:22:34.280 --> 0:22:39.600 in the water or some sort of rotting tissue, I'm 0:22:39.640 --> 0:22:42.240 always just amazed because again it is an experience of 0:22:42.280 --> 0:22:45.800 the ocean that is just unlike anything we can experience 0:22:45.920 --> 0:22:50.080 when we venture into it. And the same holds true 0:22:50.080 --> 0:22:52.840 of the cave. Like when we enter into the cave, 0:22:54.160 --> 0:22:57.399 our experiences are rather different compared to the organisms that 0:22:57.440 --> 0:23:10.159 have evolved to thrive there. Now the place I'd like 0:23:10.200 --> 0:23:13.320 to turn to next. This this gets into something that 0:23:13.560 --> 0:23:17.040 was probably one of the key reasons I decided this 0:23:17.080 --> 0:23:19.320 would be a good series for us to do, you know, 0:23:19.359 --> 0:23:21.119 to to return to cave biology. 0:23:21.560 --> 0:23:21.679 Uh. 0:23:21.920 --> 0:23:23.840 This and the fact that I was also inspired by 0:23:23.880 --> 0:23:29.320 some cave environment related stuff at the Bishop Museum on 0:23:29.440 --> 0:23:31.840 a Wahuo recently when I returned there and got to 0:23:32.040 --> 0:23:34.400 take in their natural history section in addition to their 0:23:34.440 --> 0:23:38.639 their cultural and historical sections. But yeah, this is the 0:23:38.680 --> 0:23:42.280 revelation that really pushed me over the edge that for 0:23:42.359 --> 0:23:49.000 many cave environments, bat guano is sunlight. Ooh, bat guano, 0:23:49.080 --> 0:23:53.080 that's bat poop if you will, if you if you're 0:23:53.119 --> 0:23:56.800 not familiar essentially in these environments, yes, this is the 0:23:56.880 --> 0:24:01.280 light of the sun. This plays a vital role in 0:24:01.320 --> 0:24:04.800 the food chain because remember light is the first step 0:24:04.840 --> 0:24:09.359 in the food chain of the Epigean world. Sunlight reaches 0:24:09.400 --> 0:24:14.960