There are millions of examples of plants and animals
adapting to their environment.
Need to blend in?
Change your coloring.
Need to crack a different kind of nut?
Change your beak.
But while we have lots of examples of adaptation,
we rarely have the ability to look at what
genetic changes caused the physical ones.
Not every physical trait shares the same kind
of genetic basis. An example is anteaters,
aardvarks, and armadillos. They all have
sticky tongues for catching ants even though
they aren't closely related species.
This is called convergent evolution.
Scientists at the University of Victoria in Canada have
been able to find the exact genetic changes that lead
to differences in vision in a super cool little fish called
the threespine stickleback, and it turns out that those
genetic changes are the exact same ones
that happened in the ancestor of spiny-rayed fish like
salmon, carp, and bass over 198 Million years ago!
It's super difficult to track genetic changes that
lead to physical adaptations since they usually
take place over many generations and hundreds of years.
Whereas the career of a scientist is maybe about 50 years.
If you're lucky!
To study genetic changes easily you need a place where
an adaptation is occurring multiple times on a timescale
fast enough that you can actually see it happen.
And that is exactly what these researchers did!
They looked at a small fish called the
threespine stickleback that lives in a variety of lakes in
an archipelago off the coast of British Columbia, but
it turns out that not all of these lakes are created equally.
There are two different types of lake. Clearwater and blackwater.
Clearwater lakes are just like they sound. The water
looks pretty clear and there's a lot of light so the fish
have no trouble seeing, and much like the ocean or
other bodies of clearwater, the light in them is mostly blue.
Blackwater lakes are different. They're created when
the water is stained with tannins, which are
molecules that you might be familiar with if you
jumpstart your morning with beverages like tea or coffee.
The color and astringent or bitter-ish flavor of coffee is
caused by tannins.
This tannin stained water actually absorbs most of
the blue light that's shining from the Sun, and
any light that would reflect off the sides or the
bottom of the lake is also absorbed.
This means that the fish are essentially in a lake like
a photography darkroom where the light is mostly
red and it's only shining from directly above.
Because of the huge differences between clearwater and
blackwater, the sticklebacks have adapted their
vision to one lake or the other.
But how did they do it?
To find the genetic source of the differences in
fish vision between clearwater and blackwater lakes,
the researchers took fish from each of the different
kinds of lakes and looked at their DNA to see how it was different.
But in addition to looking at fish that were already
adapted to each of their environments,
they also took some fish that were
already living in a blackwater lake and moved them to
an unoccupied clearwater lake. They then checked on
how they were adapting for the next 19 years!
Through these two types of experiments, the
researchers found the source for the vision adaptation.
It all boils down to seven amino acids in a fish eye protein that
recognizes light. Those seven amino acids help
tune that protein from being sensitive to blue light to
being sensitive to red.
Just like you would tune a radio from one station to another.
The researchers also checked out the genes of
fish that are distantly related to the
threespine stickleback and they saw that
the same amino acid changes that are happening in
the stickleback right now occurred to
those fish almost 198 million years ago!
It's pretty cool how this happened.
So about 198 million years ago in the
ancestor of all spiny-rayed fish, the gene which
encodes for the protein that recognizes
light accidentally got duplicated! Just like hitting copy and paste.
But then, over time, those two copies started to
become different. One recognized blue light and
the other copy recognized red. Exactly like what's
happening in the sticklebacks now!
But wait...
If all spiny-rayed fish have these two genes...
and the threespined stickleback is a spiny-rayed fish...
then it should already have both the blue and red sensitive protein!
It should already be able to adapt!
Well it turns out the stickleback actually lost
one of the copies, just like you might lose your
great-grandmother's pearl necklace in
going from generation to generation.
So, now they have to reevolve the same amino acid changes
to adapt to blackwater versus clearwater every time they
move into a new lake.
Like Sisyphus rolling his rock uphill!
As a major Batman nerd, I'm reminded of when Bane
says his classic quote in The Dark Knight Rises:
I choose to think that he's referring to evolution!
There is a difference between being put into a dark
environment and actually thriving there for multiple generations.
Just look at the threespine stickleback!
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