[SOUND] Okay, rapid two, rapid two. Wow, look at that whirlpool. >> Miles, That's awesome. >> Make sure we run, mark it that we gotta run on one side of those whirlpools. >> What side? >> Center right. >> Got it. The right [CROSSTALK] >> One of the most extraordinary things about the lower Congo River, is that it isn't just a band of water. [SOUND] It's an incredibly complex hydrological system. And in that unique stretch of river, are found some of the most extraordinary fishes on Earth. And the most incredible numbers of species of fish. Now we think, it's our hypothesis, that it's that complexity of hydrology that's really the key to understanding why there are so many different species of fish here. To me, one of the most important things is when we look at these rapids, I want to know how deep all of that goes because, you know, it's possible that that could be a surface phenomenon, and it may well be that for the fishes here, they can swim underneath that. I don't know, and that's exactly what we're going to find out with this equipment. >> What's going on? >> We're setting up the instruments to start recording data. >> Everything's on, we're just setting a filename for the echo sounder. It's all powered, all running, it's a, we got about 20 seconds and we're, have liftoff. [SOUND] [SOUND] It's huge, and it feels like when you paddle up to just the beach right here, it feels like an ocean, because the waves are just crashing in and breaking like an ocean. >> We want to get it out and make sure things are on and running. [NOISE] This is the depth data from the echo sounder, and as we were strolling across, it was pretty shallow. And all of a sudden the depth line just dropped off the screen. Obviously he went over some major hole. So it's a, but it's, it's beautiful. [SOUND] [FOREIGN] >> This is what the local people here call mondelli bureau. It's a completely blind de-pigmented cyclid fish. We only ever find them dead, we've never caught one, they just wash up dead. Because we think they're living very, very deep down in the canyon that's out there in the river. That Ned and John are going to be mapping for us, they're going to be able to tell us exactly how big the canyon is, and how deep it is. >> [FOREIGN] >> John, what'd you get? >> 495 feet. [SOUND] 545. 520. 510. >> So John just tells me that we're sitting over a 530 foot hole, right here. Very calm water. Not much going on. But that's pretty cool. [SOUND] >> It's going to go back through the whirlpool. >> The boat, right now, is hovering over the center of a whirlpool. So we're just spinning around and around. As you traverse this river, you'll see whirlpools that form and dissipate with radii, of literally hundreds of feet sometimes. This one is, about 20 to 30 feet across, so we're just spinning with this whirlpool, these things form, they arise, they dissipate because of the huge depth of the chasm below us. >> This was the impressive one, because were cruising along at about 415 feet, and then it drops off to 550 plus. So we got this, it's like a big crack. >> Oh, so that's where they find mundelli bureau. Right in here. >> Right at the cliff. It's that sheer wall that comes down. >> [LAUGH] That is pretty cool. >> It was pretty cool. >> That's, I mean, the velocity was extreme in there. It's pretty fast. >> And we got 10 to 14 feet a second. >> So the red and the yellow. >> Yep. >> Are the fastest. >> Right. >> What we're finding here are walls of water. [SOUND] Velocities at the surface going in one direction extremely fast, go down to a hundred meters. And they're going extremely fast in the opposite direction. [MUSIC] So there's this cacophony of water and mountains and troughs. It's a wild, wild place. And what we think is really happening is this tremendous river topology is actually serving to isolate fish populations. And that's really weird, cause we always think river's water, and if you've got water the fish can swim in it. So you're going to have no difference from one side of the river to the other side of the river because fish can swim across. Turns out not to be the case in the lower Congo. There are certain species that we're looking for, so we will sample tissues of those first. Ooh. Look at this. >> [FOREIGN] >> This is 218. Okay, so now I'm going to take a fin, from which we can extract DNA. We get some specimens from this side of the river. We look at them, we say, oh we know what that is. We go to the other side of the river. We collect the same species, we look at the specimens. We say, oh, it's the same thing. But when we go back to the lab, [NOISE] and we start analyzing the DNA. We find no, no, no, no, they're not the same thing, they're distinct. >> Once we have acquired all of this genetic information, we're able to reconstruct trees of relationships for these species, that suggest that the diversification in lower Congo is ongoing. This tree shows the relationships of populations of teleogramma brichardi collected on opposite banks of the Congo, separated by less than two kilometers. Here, we can view it in a little bit different way. This is a haplotype tree, and each circle is proportional to the number of individuals with the same genetic signal. And the lines, represent the distance between them. This says 122, out of a couple of thousand nucleotides sequenced, there are 122 mutations separating the Les Rapides population from the opposite bank population at Kinsuka. And, this is greater than 5% sequence divergence. Which is extremely surprising, for two populations of a species that look exactly the same. >> You can see how complex it is. The water is moving at so many angles. >> And at quite high velocities. >> At very high velocities. >> It's going to be really great to be able to correlate some of the genetics that Bob's been doing with now what we know about the, river in this region. >> Within the trees that we've generated of species found in the lower Congo, We do see a number of patterns emerging, that roughly corresponds to hydrologic features in the system. And there's a very strong implication that hydrologic features are serving as barriers, and driving diversification. >> Speciation to a large extent is driven by isolation. If two populations don't reproduce with each other, then over time, genetic changes will accumulate and they diverge. They may not look that different, but genetically, the genes are clicking away and they're changing. So it's almost as if we're getting a window into that speciation process. It hasn't yet happened with a lot of these fish species, but it's on the way to happening. [MUSIC]. Species are evolving all the time in the system. That explains why there are so many species there. So really, we have this just wonderful system. It's a magical place. And it's a terrific place for really studying evolution in action. [MUSIC]
