Nature puts on some spectacular light shows.
From the sight of fireflies on a summer evening, to astonishingly blue beaches, glowing creatures
are everywhere.
But… light is a form of energy, and living things don’t waste energy for nothing.
So why do they glow?
Bioluminescence, which is what it’s called when living creatures give off light, has
evolved separately dozens of times over the course of the history of the earth.
So there must be some advantage to glowing.
They’re not just doing it because it’s pretty.
Well, actually, the fireflies kinda are.
Adult fireflies use their glowing bodies to find mates, and to make sure they find the
right species, different kinds of fireflies use different patterns of flashes.
They glow using a protein called luciferase which transforms oxygen, energy from the cell’s
energy storage molecule ATP, and a special starting chemical called luciferin into light.
Super small changes to the firefly luciferase protein can shift the color of light it makes,
and fireflies glow from yellow-green to orange and red.
Why would they want to make different colors?
One possibility is that they evolved to contrast with the background colors of different habitats
so their mates can see them clearly.
A bunch of other species use different types of luciferase proteins, too -- like a tiny
crustacean called an ostracod, which has a frankly hilarious defense mechanism that you
might’ve seen on your tumblr dash or facebook feed.
When a fish spots an ostracod, it thinks “that’s a nice little snack.”
But the instant the ostracod is swallowed, it squirts out a bunch of luciferase.
Now these are tiny, tiny fish and their bellies are transparent so suddenly, the fish’s
stomach is glowing bright blue, which is a signal to larger predators that want to eat
that fish that: There is a tasty snack right there!
Now the little fish doesn’t want that, so it barfs up the ostracod, and the glowing
stuff, and swims for its life.
A lot of times when I’ve seen people share this they think that the fish is actually
spitting out glowing light stuff like a Night Fury in How to Train Your Dragon, but it’s
not, it’s spitting out a glowing organism that doesn’t want to be eaten.
So the ostracod lives to glow another day.
Another blue glow-er, sea sparkle, isn’t even an animal -- it’s a type of creature
called a protist.
It floats in the ocean as plankton, not doing very much.
But when it’s disturbed by predators, or even just choppy surf, it activates its own
version of luciferase.
Why sea sparkle does this isn’t entirely clear, but it might be similar to the reason
the ostracods do it: when sea sparkle is glowing, predators tend to avoid eating it.
Whatever the reason, when it blooms, in places like Hong Kong and the Maldives sea sparkle
can turn the water by the shore a brilliant blue.
Best of all, unlike lots of its close relatives, sea sparkle isn’t toxic to humans.
If you’re lucky enough to be around for one of these blooms, it’s safe to swim and
surf in, and the blue light will follow you around like a personal glowing trail.
Most marine life that glows, like the ostracod and sea sparkle, produce blue light because
it travels best through water.
But there’s an interesting -- and scientifically important -- exception.
One species of jellyfish, the crystal jelly, glows green.
To do that, it uses two proteins.
The first one, aequorin, actually does make blue light.
The second, protein, called GFP, is fluorescent, meaning that when it’s hit by one color
of light -- in this case, the blue from aequorin -- it absorbs some of its energy, then releases
a lower-energy version of that light: green.
Why the jellyfish shifts its glow from blue to green, or why it glows in the first place,
no one knows.
It’s tough to see the crystal jelly’s bioluminescence at all unless researchers
disturb it, so we can’t tell what it uses it for when no one’s watching.
Now, we may not know what the jellyfish uses its light for, but scientists use it for a
lot of things, like making cellular structures visible under a microscope.
So in 2008, GFP’s discoverers shared the Nobel Prize in Chemistry for finding a way
to make things light up in the lab.
Luciferase, especially from fireflies, has its uses too, mostly in helping us discover
what conditions you need to turn on genes.
You just replace the gene with luciferase, and you’ll see it light up when those conditions
are met.
Not only have these creatures have evolved ways to make themselves seen -- their glowing
proteins let us see the life we study, too.
So we can thank fireflies for both blinking lights on warm summer evenings, and for advances
in biology and medicine.
So thank you fireflies… and thanks for watching, though I don’t really know why fireflies
watch Youtube videos.
It’s another unexplained mystery of science.
And also, I’ve got to thank everyone else who’s watching.
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