Hi. It's Mr. Andersen and in
this podcast I'm going to talk about stickleback
evolution. Charles Darwin's idea of natural
selection has pretty much remained unchanged
until this day. Unfortunately he didn't do
a lot of experimentation on natural selection
back then. And they really didn't know that
you could observe it nature and we really
have done a ton of that in the last 100 years.
And so if we look right here, this is the
story of the peppered moth, remember how that
evolved. Or the work of Peter and Rosemary
Grant on the finches of the Galapagos. They
studied it for decades. Or the work on guppies
in Trinidad. So there's a lot of data out
there of organisms evolving over time. But
in this one I'm going to talk about evolution
in the stickleback which is an unlikely kind
of hero. This unlikely fish. And the ones
I'm going to talk about are found in Alaska.
As I talk about evolution, I really want you
to understand that evolution is pretty much
the same throughout all of nature. We sometimes
delineate between micro-evolution and macro-evolution
where micro-evolution is change in the gene
pool and we'll see that in the stickleback.
And then macro-evolution is speciation or
the formation of two species from one. Most
scientists would say that there's really no
difference between the two. All we're doing
is it's organisms that are adapting to their
local environment. And we can see both of
these at play in the stickleback. So let me
tell you the story of the comeback stickleback.
If you're interested in this, here's a little
weblink, and I'll put that down in the video
description as well so you can look at the
research that was done on these stickleback
fish. And so basically the story starts back
in the 80s. And so we had a group of stickleback.
These are fresh water stickleback. They're
perfectly adapted to this environment in Loberg
Lake which is not a big lake right outside
of Wasilla, AK. And basically they were having
a great time. And then in 1982 the lake was
poisoned. And it was poisoned to get rid of
all fish so they could reintroduce some trout
into the area. And so all these perfectly
evolved sticklebacks died. And so it was an
empty lake. But a few years later Anadramous
stickleback, and that's a huge word, I'm happy
I said it right, it basically means they swam
their way back from the ocean. Made it into
Loberg Lake. And they started reproducing.
Now the difference between the two, hopefully
you saw it, is that these ones are going to
have bigger spikes, these marine sticklebacks,
or ones that are found in the ocean. And they
have all these armored plates on the side.
In fact we call them fully armored stickleback
on the side. And the reason they look that
way is that these are the main predators of
them when they are out in the ocean. It's
going to be trout, it's going to salmon and
things like that. And so these aren't here
anymore in this Loberg Lake. And so they started
reproducing and their numbers started to increase
to the point where scientists started to note
them. Now once you make it to the lake, obviously
there's going to be a predator here as well.
So this is the dragon fly larva. And the dragon
fly larva loves to grab on to sticklebacks
and then eat them. And so the sticklebacks
that used to be in the lake had kind of evolved
defense to this. The old sticklebacks grow
really really fast and so they don't spend
a lot of time being small enough that they
can actually be preyed upon by this dragon
fly. And also all these spikes and plates
are a disadvantage because it makes it easier
to grab on to that stickleback. And so basically
what happens is we have growth of the stickleback,
they start to do well but we also have these
dragon flies that are doing well just eating
them. And so this is when the scientists show
up. And I'll show you data in just a second.
So 1990, almost all of the stickleback are
going to be of this fully armored anadramous
made it from the ocean kind of a class. And
so over time what the scientists start to
observe is the number of those that are fully
armored starts to decrease and the number
of those that are not fully armored start
to increase. So the low armored stickleback
start to increase. Until today we have all
of those sticklebacks looking like the ones
that were probably originally there before
the poisoning. And so this is the researchers.
So this is from Bell Lab. And this is Michael
Bell. I had a little brief email exchange
with him and he said feel free to use any
of the data. He thinks this is a great example
of natural selection. He thought it was important
that we share this with students around the
world. And so thank you Michael for sharing
that with me. And thank you for everybody
else who collected the data so that we can
see it. And so basically this is a summary
of their data. So in 1990 they show up. And
there's not hardly any of these low armored
sticklebacks. But as they start observing
it over the next twenty years we see an increase
in the low armored sticklebacks and then we
see a decrease in the fully armored sticklebacks.
And there's really one gene that's determining
the number of plates that we have on each
of the different fish. Now lots of times we
see data represented like that but we really
miss what's going on. And so let's kind of
dig our way into the data that they collected.
This is some example. So basically what they
were doing in this, these researchers were
grabbing the sticklebacks. All the one, every
summer they'd go to the lake they'd catch
as many sticklebacks as they could, they'd
dye them, so they don't really look this red
color, but they dye them so they can see the
plates on the side. And then they would basically
take one fish and they'd count the number
of plates on the side. So starting up at the
top they count the total number of plates,
and then they would simply graph that. So
in 1990 most of them are going to have around
33 plates on the side. And there's some that
have a little bit less and some that have
a little bit more, so we have variation. We
have this bell shaped curve. And then they
simply go back year after year after year.
So let's look what happens in 1991. We start
to see a few of these low armored show up.
They only have seven plates. They only have
these plates up towards front. If we keep
going, what we see so now we're four years,
five years later we're starting to see what's
called directional selection. So those dragon
flies are targeting the ones that have fully
armored and we're starting to see an increase
in the low armored. We call this micro-evolution.
We're changing the gene pool and if we ever
change the frequency in the gene pool evolution
occurs. And so let's watch what happens over
the next, from 1998 to 1999 and they keep
collecting this data all the way until the
year 2008. And so we see directional selection.
So we're moving towards a bell shaped curve
that has less of these armored plates. And
so we still have variation and we still have
a few of these fully armored left in 2009,
but we've seen micro-evolution. We've seen
change from this fully armored slow growing
marine like fish to the one that looks a lot
like the fish that were there before they
were actually poisoned. So we see evolution
taking place. I think this is a great example
of micro-evolution or change in the gene pool.
And it really didn't take that long. We like
to think of evolution must take millions or
thousands of years to occur. This took, you
know, less than a lifetime. It took two decades
to observe a complete change in the phenotypes
of these fish. So that's neat. And when I
asked Mike if we could use the data he sent
me some more data. Data that they've collected
since then. So this is published in 2012.
And I think this is really cool. So basically
in this study what they did is they wanted
to see if speciation is occurring. And so
this is a phylogenetic tree. So basically
how do you read a phylogenetic tree, time
is going to go from the left to the right
and every time we have a branch point that
means there was a common ancestor here and
then we have a line, a different lineage that
comes from that. And so what they were looking
at in this study were these Loberg sticklebacks.
They then found some sticklebacks in Rabbit
Slough which is just a few kilometers away.
And they thought this is a good representation
of what this first group of sticklebacks that
made their way into the lake look like. You
can see that it looks a lot more like a marine
type of stickleback. And then they found some
sticklebacks from Corcoran Lake which is 40
miles away. And so these were probably shared
ancestry with Loberg Lake and those of Rabbit
Slough, but it's really a long time ago. And
so how do we know who's related to whom? We
can just do genetic analysis of all these
fish and we can see who's related to who based
on the DNA and how the DNA has changed over
time. And so what they wanted to see is if
there was starting to be reproductive isolation.
And so basically what they would do is put
these males is a tank and see how many of
the females would mate with them. And surprisingly,
even though is it was probably twenty years
since they diverged as a species, the females
in the Loberg Lake were ignoring those in
Rabbit Slough. And the researchers think that
had to do with just their physical appearance.
The way they looked. And they were larger
and different in shade, they weren't willing
to mate with them. However, they were willing
to mate with those that they diverged from
a long time ago. And so what they'd shown,
not only have the sticklebacks changed, but
now they were not reproducing with each other.
And so basically what does that mean? Well
the point at which they fail to mate with
each other, we've now created two species.
So we've gone from one to two. And so that's
pretty amazing data. And so the stories of
the stickleback continue to amaze us and impress
scientists as well. And so thanks for the
data and thanks for watching. And I hope that's
helpful.
