Biology / The Strange

A single-celled organism with a small human-like ‘eye’

— Billy Wright

SCIENTISTS STUDYING MICROSCOPIC LIFE IN SEAWATER have found, what we laypeople might call, a tiny floating eyeball. Just as with our own eyes, the creature is fitted with a lens, cornea and retina. But what’s remarkable is that it’s all inside the one cell.

Scientists from the University of British Columbia (UBC) had their research on the ‘Warnowiid’ published last month in Nature.

“It’s an amazingly complex structure for a single-celled organism to have evolved,” said lead author Greg Gavelis, a zoology PhD student at UBC, speaking about the warnowiid.

“It contains a collection of sub-cellular organelles that look very much like the lens, cornea, iris and retina of multicellular eyes found in humans and other larger animals.”

The scientists still aren’t entirely sure what the eye is used for. Without the billions of very purposeful cells found in our own eyes, the warnowiid would have a very different view of the world.

Mitochondria, the 'powerhouse' structures of a cell, interlock and curve to form the cornea. Photosensitive plastids function as the retina. Image: Gavelis, G.S. et al. 2015, Nature.

Mitochondria, normally the ‘powerhouse’ structures of a cell, interlock and curve to form the warnowiid’s cornea. Photosensitive plastids function as the retina. Image: G.S. Gavelis, et al. 2015, Nature.

The creature uses a small harpoon-like structure to hunt for prey within clouds of plankton. Many of the small organisms it goes after are transparent. Researchers speculate that the warnowiid uses its one eye to detect small shifts in the light passing through the transparent bodies of its prey. The structure could then send chemical signals to other parts of the cell, dictating the direction of pursuit.

Warnowiids reside in the shallows off the coasts of Canada and Japan, and they were in fact first discovered over a century ago. But studying the creature proved difficult, as it rapidly begins to disintegrate as soon as it’s taken out of water.

To catch a warnowiid, Gavelis spent a year searching samples of seawater with a microscope. After finally spotting one, Gavelis froze it in plastic resin, like a mosquito in amber. From there the warnowiid was studied using electron microscopes, as scientists made a three-dimensional reconstruction of the creature’s subcellular eye.

It appears that through evolution, the warnowiid has repurposed cellular structures that are usually responsible for other functions, assembling them together into a makeshift eye.

For instance, the creature’s ‘cornea’—the transparent outer layer of an eye that refracts light against a lens—is made up of mitochondria, organelles normally involved in the production of energy. The mitochondria of the warnowiid are instead found interlocked and curving in such a way as to concentrate incoming light on the creature’s ‘retina’.

The retina, researchers found to be rich in algal DNA, indicating that it probably came from something the warnowiid ate at some point—namely, a stray piece of algae. Whereas plants and algae photosynthesise energy from sunlight, the warnowiid has absorbed and repurposed this function to meet its predatory disposition. Instead of light-capturing panels, the warnowiid evolved a rudimentary light-sensing organ.

It appears as though the outer layers of the warnowiid’s eye concentrate light against this retina to increase sensitivity (rather than focusing light as our own eye does).

With its retina tickled, chemical impulses spur the eye-thing forward to harpoon against the blurs and lightstreaks of a microscopic water world.

For scientists, charting the warnowiid is a juicy step forward in tracing the foundations of larger animal eyes — naturally ingenious and almost unbelievably complex pieces of equipment. The simple subcellular eye of the warnowiid is a clue that our own eyes, millions of eyes ago, may have started out as something quite similar.

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I move on an Earth that fizzes like acid flesh. I swim in the sores, the bad swamps, my strokes in rhythm to a strange floodlight. A warm current passes soft along my back and I smile. My big eye is open. I look out at a great white sheet, luminescent and rippled against the ebb of the land.

But they come. Slowly at first, for millions of years these creatures prod and nose the sheet. They leave teeth marks. And soon they bring hooks. They punch holes and make long rips. Now I swim low, in the dark black. Wary for some lethal horror that would come fast in coloured flashes.

I flee the ocean. Dry, crippled and heavy. I grow bristles. I’m tied to a stick, sunburnt. Around me the world blooms green like a gas cloud. I am hungry, but this fruit has made me sick.

I do not eat the dead. I don’t want to go to hell. Instead I drive, to the office, to the ocean. My neck is stiff and it hurts. Somewhere around here there is a world, I think. So in the distance I look to a great white sheet in the sky. Symbols appear, scrolling. I have travelled such a long way to be with you again.

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