WEBVTT

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Anyway, again, sitting
out in the field,

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we've watched 61
individuals in nature

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continuously for six hours
each recording on computer

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all their little behaviors.

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And I'm just going to
show a couple of pictures.

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This is my former
student, Mike, and I

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watching some of
these caterpillars

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in the field in the
Santa Rita mountains.

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In fact, here's one
of the caterpillars.

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And we could usually
watch two at once

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and record all the
things they did

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because we had these
little handheld computers.

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We had various people help us.

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So this was a Brazilian
student, Danny,

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who worked with
us for six months.

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And we had a variety
of people come.

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They liked to come
for a little while.

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They don't want to do
it as long as we do.

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[LAUGHTER]

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And Thomas Hartmann, who's
my collaborator from Germany,

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came out one summer and
spent the summer here

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watching caterpillars.

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He's the biochemist in the team.

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And he does all the chemistry
and the molecular biology.

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So he's really a lab
person, but he had fun.

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But after six hours of watching,
he was very pleased to get up.

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[LAUGHTER]

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Anyway, just some
basic information

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to give you an idea of what
these caterpillars are like.

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Number of plant species eaten
in six hours on average, five.

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Number of individual plants
eaten in six hours, nine.

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Because they move around a lot,
so they go from place to place.

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They walk on things.

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Number of plant parts
and species in six hours.

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So we're talking leaves,
flowers, fruit stems,

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that kind of thing, 21.

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The number of plant species
recorded as host, 79.

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The percent of plant
species rejected

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in six observations, 49.

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So half the plants they come
across they eat, and half they

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reject.

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But you can see they're
real generalists.

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They eat loads and loads
of different plants.

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But what they like
are plants containing

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toxins called cool pyrrolizidine
alkaloids, otherwise known

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as PAs.

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I'm going to talk about PAs.

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Here's a molecule of a PA.

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It's a complicated molecule.

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It's a poisonous chemical.

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Poisonous to pretty well
everything except these kinds

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of caterpillars.

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I've put part of it in red
because they don't just

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use these things for defense.

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They take a part
of this molecule

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and make it into a
courtship pheromone.

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So the males produce
this thing, and it

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makes the females want
to mate with them.

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So they have a lot of uses.

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Now, again, we go
back to behavior.

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Caterpillars wander around.

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On first contact with the
plant, 100% acceptance

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of plants containing
PAs, but less

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acceptance on other
nutritious plants.

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So here are two PA plants.

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100% likelihood of feeding
if they encounter them,

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but somewhat less on
all the other plants.

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So we know that they like
these plants containing

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PAs, which makes sense because
they want those chemicals.

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And this is a summary slide
of a large amount of work,

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as you might imagine.

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But the PAs
sequestered from plants

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provide protection from
a lot of natural enemies.

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And here are different things.

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The sucking bugs, the mantids,
the lacewings, the wasps,

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spiders, ants.

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You name it.

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These chemicals protect
the caterpillars

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from a lot of
different predators,

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and they're very effective.

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So it's a good strategy.

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So Estigmene mainly sequester
pyrrolizidine alkaloids

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efficiently, concentrating
trace amounts in foods

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to levels that are
biologically useful.

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Now here's where Thomas came in.

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Thomas Hartmann in
Germany, of course,

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did all the analysis
of the things

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to show the plants
didn't have much,

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but the caterpillars
had huge amounts.

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So they're very effective.

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Males and females
equally accomplished.

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PA is found throughout body,
but high concentrations

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in the integument.

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Makes sense.

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If you're a predator, you want
to know the bad taste quickly.

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Males donate PAs to
females during copulation,

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and the females endow their
eggs with these chemicals.

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So the eggs are protected.

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And the males produce
the courtship pheromones.

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So basically, PAs matter.

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That's the whole point.

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They like the plants.

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They like the PAs.

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The PAs are terribly important
to them biologically.

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So the interesting
thing, then, was

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to look at how they
taste these things.

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And so I've put a very
simple schema here of a taste

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bud of a caterpillar.

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[LAUGHTER]

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They have taste buds like we do.

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And each taste bud has
four taste cells in it,

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and I've shown each one
as a separate color.

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Four taste cells.

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And these things
join up to the brain.

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So it's a regular taste bud.

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And then you can
record from them.

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And what I do is I have
a glass electrode here

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and a silver wire
in the middle, too.

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So if a chemical that
tastes on one of these cells

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causes a firing of the cell,
you get electrical impulses.

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It's transmitted
through the material

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here, through a salt solution,
onto the silver wire.

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And the silver wire's connected
to all kinds of amplifiers

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and filters to a computer.

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So what we can do is we
have a salt solution in here

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to carry the electrical
impulse, and then it

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goes onto the silver wire.

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But we can also put
in this salt solution

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various chemicals to see which
ones these cells respond to.

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Now there are four cells, and
we're recording all of them

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together.

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But each cell produces a very
different pattern of firing,

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so we can identify
the different cells.

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And you'll see
it's pretty small.

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So here's the scale.

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0.1 of a millimeter
is this length.

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So we're talking pretty
small stuff here.

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So I have to pull these
little glass electrodes out

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to make a very small end.

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Here are the two main taste
buds of the caterpillars.

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So there's a lateral one.

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This is right out here.

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And a medial one, which is
sort of more in the middle.

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And each of them has
these four cells.

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And usually, there are two that
say yes, and two that say no.

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Just like for us, sweet says
yes, and bitter says no.

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We have the same kind of
situation in caterpillars.

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So here, the salt and
the bitter chemicals

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will be going to a part
of the brain that says no,

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and the cells responding
to PAs and the cells

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responding to sugars says yes.

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So the balance of these
things will tell it

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whether to eat or not.

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There's a little bit of
difference in the two taste

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buds.

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But basically, there's
two yeses and two nos.

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And the yeses in
each case have a cell

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that is specific to the PAs.

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So we don't have such
thing, but these guys do.

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And the sensitivity
is incredible.

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We're talking 100,000
times more sensitive to PAs

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than we are to sugar.

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So it's the most
sensitive taste cells

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that have ever been found.

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So anyway, I record from these.

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And this is the sort
of result I get.

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So in half a second,
I get these records.

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And each one of
these little spikes

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means that there's
a nerve impulse.

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And so if you look at
the salt, the salt cell

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is responding here to
the presence of the salt.

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And here's the response
to PA, a different cell,

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a different shaped spike.

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But each one of
these little spikes

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represents a nerve impulse
on their taste cell.

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So we can determine
which cell's which

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by the shape and
size of these spikes,

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and eventually work
out which cells

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are responding to which things,
and how sensitive, or specific

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they are.

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Anyway, it's rather
handy that the PA cell

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has these great, big
spikes because it makes

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it nice and easy to identify.

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And as I said,
extremely sensitive.

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Now going back to the behavior.

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Although the PA plants are
always accepted initially,

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repeated encounters
lead to rejection.

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So this is what you saw before.

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The PA plant's first encounter,
always accepted 100%.

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The other plants varied.

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But when you look
at later encounters,

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this starts dropping.

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They stop wanting it anymore,
whereas the pattern is rather

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variable with other plants.

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But the PA plants you'd think,
jeez, they want all this stuff.

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It's so important for them.

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They should stay
there, but they don't.

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And after a while, they
leave those plants.

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So one of the things
that interested us was,

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why did they leave
these plants when

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they need this stuff so much?

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It's so important
in their lives.

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That was one of the
reasons why we studied it.

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Well, we fed them
on the PA plants

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for different periods of time,
and looked at the response

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of those PA cells.

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And you see, here you
are at the beginning.

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We're getting 40
spikes per half second.

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But if they fed on these
PA plants for a while,

00:09:36.620 --> 00:09:37.440 align:middle line:90%
it goes way down.

00:09:37.440 --> 00:09:40.040 align:middle line:84%
And some insects, there's
nothing left at all.

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Insects, they just
stop responding.

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We don't get that kind
of thing in humans.

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Your taste cells are
more or less constant.

00:09:46.790 --> 00:09:49.940 align:middle line:84%
They do what they're supposed
to do whatever you eat.

00:09:49.940 --> 00:09:53.180 align:middle line:84%
But in these caterpillars, if
they eat a lot of PA plants,

00:09:53.180 --> 00:09:56.510 align:middle line:90%
the PA cell stops responding.

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With Lavender.

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Isn't there a smell
difference there?

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Well, you do get used to smells
and stop responding to smells.

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[INAUDIBLE] smell.

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Yeah, in a lot of
cases, that's true.

00:10:07.170 --> 00:10:09.890 align:middle line:84%
But it usually doesn't
happen with your taste buds.

00:10:09.890 --> 00:10:13.160 align:middle line:84%
It happens with your smell
that you get used to a smell

00:10:13.160 --> 00:10:14.630 align:middle line:90%
and stop responding.

00:10:14.630 --> 00:10:17.990 align:middle line:84%
And anyway, when you stop
responding to a smell,

00:10:17.990 --> 00:10:19.640 align:middle line:90%
it's a short-lived thing.

00:10:19.640 --> 00:10:23.120 align:middle line:84%
You get fresh air again, and
you immediately smell it again.

00:10:23.120 --> 00:10:25.055 align:middle line:84%
Of course, this lasts
quite a long time.

00:10:25.055 --> 00:10:26.015 align:middle line:90%
It lasts for hours.

00:10:26.015 --> 00:10:29.645 align:middle line:90%


00:10:29.645 --> 00:10:37.100 align:middle line:84%
What we did was we injected
PAs into the caterpillar's

00:10:37.100 --> 00:10:40.400 align:middle line:84%
bloodstream, and found that
it shed off those taste

00:10:40.400 --> 00:10:44.000 align:middle line:90%
cells in the same way.

00:10:44.000 --> 00:10:44.840 align:middle line:90%
Here we are.

00:10:44.840 --> 00:10:51.950 align:middle line:90%
Over 40 spikes per half second.

00:10:51.950 --> 00:10:55.340 align:middle line:84%
And if you inject them
with just a plain saline,

00:10:55.340 --> 00:10:57.450 align:middle line:90%
it doesn't change over time.

00:10:57.450 --> 00:11:01.940 align:middle line:84%
But if you inject them with the
PAs, the response falls off,

00:11:01.940 --> 00:11:03.725 align:middle line:84%
and it lasts for
a couple of hours.

00:11:03.725 --> 00:11:06.950 align:middle line:90%


00:11:06.950 --> 00:11:11.570 align:middle line:84%
What's interesting about this
is that when they feed on the PA

00:11:11.570 --> 00:11:14.450 align:middle line:84%
plants, these PAs are
in the bloodstream

00:11:14.450 --> 00:11:18.770 align:middle line:84%
and clearly has some kind of
feedback on the taste cells

00:11:18.770 --> 00:11:20.330 align:middle line:90%
that stops them responding.

00:11:20.330 --> 00:11:23.320 align:middle line:90%


00:11:23.320 --> 00:11:27.760 align:middle line:84%
We injected the
amounts of PAs that

00:11:27.760 --> 00:11:29.860 align:middle line:84%
reflected exactly what
happened naturally.

00:11:29.860 --> 00:11:33.220 align:middle line:84%
So you analyze the blood,
find out the amount of PA

00:11:33.220 --> 00:11:35.650 align:middle line:84%
in the blood, and then you
inject that amount of PA

00:11:35.650 --> 00:11:37.180 align:middle line:84%
in the blood for
these experiments.

00:11:37.180 --> 00:11:39.880 align:middle line:84%
So it required quite a
lot of preliminary work

00:11:39.880 --> 00:11:46.110 align:middle line:84%
to actually get it into a
biologically reasonable amount.

00:11:46.110 --> 00:11:47.000 align:middle line:90%