Clues to prehistoric times, found in blind cavefish | Prosanta Chakrabarty

80,122 views ・ 2016-08-09

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Ichthyology,
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the study of fishes.
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It looks like a big, boring word,
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but it's actually quite exciting,
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because ichthyology is the only "ology"
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with "YOLO" in it.
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(Laughter)
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Now, to the cool kids in the audience,
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you already know, YOLO stands for "you only live once,"
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and because I only have one life,
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I'm going to spend it doing what I always dreamt of doing:
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seeing the hidden wonders of the world and discovering new species.
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And that's what I get to do.
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Now, in recent years, I really focused on caves for finding new species.
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And it turns out, there's lots of new cavefish species out there.
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You just have to know where to look,
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and to maybe be a little thin.
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(Laughter)
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Now, cavefishes can tell me a lot about biology and geology.
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They can tell me how the landmasses around them have changed and moved
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by being stuck in these little holes,
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and they can tell me about the evolution of sight, by being blind.
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Now, fish have eyes that are essentially the same as ours.
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All vertebrates do, and each time a fish species starts to adapt
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to this dark, cold, cave environment,
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over many, many generations, they lose their eyes and their eyesight
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until the end up like an eyeless cavefish like this one here.
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Now, each cavefish species has evolved in a slightly different way,
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and each one has a unique geological and biological story to tell us,
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and that's why it's so exciting when we find a new species.
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So this is a new species we described, from southern Indiana.
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We named it Amblyopsis hoosieri, the Hoosier cavefish.
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(Laughter)
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Its closest relatives are cavefishes in Kentucky,
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in the Mammoth Cave system.
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And they start to diverge when the Ohio River split them
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a few million years ago.
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And in that time they developed these subtle differences
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in the genetic architecture behind their blindness.
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There's this gene called rhodopsin that's super-critical for sight.
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We have it, and these species have it too,
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except one species has lost all function in that gene,
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and the other one maintains it.
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So this sets up this beautiful natural experiment
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where we can look at the genes behind our vision,
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and at the very roots of how we can see.
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But the genes in these cavefishes
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can also tell us about deep geological time,
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maybe no more so than in this species here.
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This is a new species we described from Madagascar
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that we named Typhleotris mararybe.
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That means "big sickness" in Malagasy,
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for how sick we got trying to collect this species.
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Now, believe it or not,
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swimming around sinkholes full of dead things
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and cave full of bat poop
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isn't the smartest thing you could be doing with your life,
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but YOLO.
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(Laughter)
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Now, I love this species despite the fact that it tried to kill us,
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and that's because this species in Madagascar,
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its closest relatives are 6,000 kilometers away,
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cavefishes in Australia.
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Now, there's no way a three-inch-long freshwater cavefish
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can swim across the Indian Ocean,
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so what we found when we compared the DNA of these species
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is that they've been separated for more than 100 million years,
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or about the time that the southern continents were last together.
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So in fact, these species didn't move at all.
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It's the continents that moved them.
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And so they give us, through their DNA,
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this precise model and measure
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of how to date and time these ancient geological events.
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Now, this species here is so new
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I'm not even allowed to tell you its name yet,
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but I can tell you it's a new species from Mexico,
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and it's probably already extinct.
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It's probably extinct because the only known cave system it's from
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was destroyed when a dam was built nearby.
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Unfortunately for cavefishes,
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their groundwater habitat
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is also our main source of drinking water.
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Now, we actually don't know this species' closest relative, yet.
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It doesn't appear to be anything else in Mexico,
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so maybe it's something in Cuba,
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or Florida, or India.
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But whatever it is, it might tell us something new about the geology
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of the Caribbean, or the biology of how to better diagnose
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certain types of blindness.
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But I hope we discover this species before it goes extinct too.
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And I'm going to spend my one life
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as an ichthyologist trying to discover and save
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these humble little blind cavefishes
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that can tell us so much about the geology of the planet
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and the biology of how we see.
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Thank you.
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(Applause)
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