![](https://assets.vice.com/content-images/contentimage/158909/anus-fish.jpg)
Annons
Prosanta Chakrabarty: Well, the coolest thing is that it's the first subterranean cave fish that's been found in North America in 40 years. We sort of made this discovery based on molecular work that my coauthor Matthew Niemiller did, and it's telling us about the evolution of blindness and how, in some cases, like this one, the genes are catching up with the morphology. So the change to a subterranean lifestyle happened well before the loss of function of some of the genes related to their lifestyle.
Annons
Yep. They don't have eyes.And at some phase in their evolution their ancestors had eyes?
Their ancestors had eyes, and when they entered these cave habitats they lost them.Okay, but how does that make this fish special?
This is kinda cool: There are about 150 species of fish that have become cave fishes. They've lost their eyes. They've lost pigmentation. It's happened at least a couple of dozen times. And every time they do this it's a new way of evolving blindness. There's no light. It's pretty much a constant temperature. So it's a very different environment than what we live in, where sight is very important. In a cave, even if you had eyes, you wouldn't be able to use them. It's pitch black.So this random mutation knocked out rhodopsin [the gene for vision] in one of the species, but not the species we just described. It's still producing a functioning gene, even though that gene basically doesn't do anything. It just shows you how finicky these mutations are when they come about. You can still have a functional gene for something, even though you lack the eye altogether.So it's one of those inefficient evolutionary remnant things? Like when Richard Dawkins dissected that giraffe and proved that some nerve was going all the way up and down its gigantic neck for no reason?
I don't think I know that story, but there's weird things about giraffes for sure. There are remnants even in humans. We have organs that don't serve much of a purpose, and things that aren't well-designed. Our heart is pretty crappy. It's not simple explaining any organism. You would think going blind would be easy, and it sorta is, but it shows you that it's not always the DNA that goes first.
Annons
Well, it's really bizarre. So some people say it's to poop out of the water. So they can lift their bodies out of the water and poop on land. But they all figure that it's also to get the eggs inside the gills. It's a cloaca, but functionally it's mostly an anus. But eggs are coming out of that hole too. Everything comes out of there.So having [its anus] right behind the head allows the eggs to get more simply into the gills, which is where these guys brood their young. Nobody's observed this, but we know its closest surface ancestors do this, so we're assuming it's for the same reason. One odd thing is, we're not sure how fertilisation happens, but that might be facilitated by having the cloaca-head-neck-anus.So they sort of, at the same time, push their heads and anuses together, and that might be how mating occurs?
Yeah, we think it might be mouthbrooding. Sperm comes through the mouth, then through the gills and then it's fertilised. It's a possibility, but it's the one that makes the most sense.So you're saying that it effectively poops sperm into its mouth?
Yeah, maybe. That's our best guess. Lots of fish actually have mouthbrooding, where the females are taking up sperm into their mouths where they also have the eggs. With these guys we're saying that's essentially pushed into the gills as well. They're freaky.
Annons
Well, if you don't have eyes and you can't see where your babies are, you'd want to keep them pretty close. That's about as close as you can get without developing internal fertilisation, which has only happened a few times. This allows them to kind of protect their young.But even for a blind fish, that's like being pregnant in your lungs, isn't it?
It also means the young get more oxygen. They get more water flow, because, in caves, usually the water gets pretty stagnant. So this will allow more water to flow over them, which allows more gas exchange, which will help them develop.So it's not just a safe place?
No. There's certainly an advantage to having your babies brood in your gills.The other thing I wanted to ask is, did you name it as an insult to Hoosier basketball because you're at rival schools?
No. Matt grew up in Indiana. He was really excited about naming it that. He's a huge Hoosier fan. I can't talk to him during basketball season. The name is in praise of the University of Indiana for starting North American ichthyology. But it's weird how the anus is news, and I don't know if you saw the Gawker article, where they said it looks like a dick…Oh, the Gawker picture definitely looks like a dick.
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