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