A single-celled marine plankton evolved a miniature version of a multi-cellular eye, possibly to help see its prey better, new research shows.
In fact, the 'ocelloid' within the planktonic predator looks so much like a complex eye that it was earlier mistaken for the eye of an animal that the plankton had eaten.
"It is an amazingly complex structure for a single-celled organism to have evolved," said lead author Greg Gavelis, a zoology PhD student at University of British Columbia (UBC).
"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," Gavelis said.
Scientists do not excatly know how the marine plankton, called warnowiids, use the eye.
Warnowiids use small harpoon-like structures to hunt prey cells in the plankton, many of which are transparent.
The eye helps warnowiids detect shifts in light as it passes through their transparent prey.
The structure could then send chemical messages to other parts of the cell, showing them in which direction to hunt.
"The internal organisation of the retinal component of the ocelloid is reminiscent of the polarising filters on the lenses of cameras and sunglasses," said senior author Brian Leander and zoologist at UBC .
The team analysed the eye-like structure using state of the art microscopy that enabled the reconstruction of three dimensional structures at the subcellular level.
The work sheds new light on how different organisms -- in this case warnowiids and animals -- can evolve similar traits in response to their environments, a process known as convergent evolution.
"When we see such similar structural complexity at fundamentally different levels of organisation in lineages that are very distantly related, then you get a much deeper understanding of convergence," Leander said.
The study was outlined in the journal Nature.
