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.