| koko |
Posted
on 23-Aug-01 11:55 AM
In fact, the microscopic lenses that coat the armor of this particular sea creature, known as the brittlestar, are so perfectly designed, some argue they rival any man-made technologies.
"I believe the performance of its lenses is really superior to anything we've been able to create before," said Joanna Aizenberg of Bell Labs in Murray Hill, N.J., who authored a study about the complex optical system of the brittlestar in this week's issue of Nature. "It is so perfect, it will be difficult to imitate in the laboratory."
Aizenberg believes studying the brittlestar's compound eye could help scientists develop better light-based data processing and optical displays, according to Roy Sambles, a physicist at the University of Exeter in Exeter, Great Britain.
Armor and Eye in One
Brittlestars, also known as serpent stars, inhabit tropical reefs around the world and have (usually five) long, slender arms extending from a central disc. Coating the surface of their arms, the animals have cuticles made of chalk-like calcium carbonate crystals — or calcite — for structural support. In some species, Aizenberg learned, this protective plate also helps the creature see.
The cuticles of certain brittlestar species are made up of tiny natural lenses, as evident in this scanning electron microscopic image. (Lucent Technologies/Bell Labs)
The protective plates of the brittlestar species Ophiocoma wendtii are made up of thousands of rows of very regular, microscopic bumps that are shaped as perfect lenses. After placing a light-sensitive lithograph under a section of the brittlestar's cuticle, Aizenberg revealed the tiny bumps focus spots of light toward a grid of regular points. And those points correspond to the location of nerve clusters under the brittlestar's skin.
By channeling light directly to its nerve clusters, the brittlestar can respond to the passing shadow of a predatory fish in a split second.
"We've known for a long time that these animals are very sensitive to light, but we've never really understood how," says Lee Ann Clements, a marine biologist at Jacksonville University in Jacksonville, Fla. "This is why the research is so exciting."
Aizenberg and researchers at the Weizmann Institute of Science in Israel and Gordon Hendler, a marine biologist at the Natural History Museum in Los Angeles County, first caught on to the brittlestar's light-sensing eye when trying to understand why the animal appeared to be using reverse camouflage.
In the day, the brittlestar turns a darker shade of reddish brown and at night, it fades to light shades of gray. Hendler realized the color change are not a botched attempt at camouflage, but a biological substitute for sunglasses.
Biological Shades
Pigment-containing cells gather over the surface of the animal's microscopic lenses during the day and effectively filter light for the brittlestar's vision system. At night, the dark cells retreat inside tiny crevices of the animal's cuticle and the lenses become bare, lighter in color, and more sensitive to light.
"The whole system works like a pair of prescription sunglasses," says Hendler.
The keen, light-sensitive eye of this particular brittlestar seems to have lent the sea creature an evolutionary edge. When analyzing the stomach contents of fish in the Caribbean, Hendler found the predators had gulped down more of the non-light-sensitive brittlestar species than ones equipped with the compound eye.
For scientists, the next step will be to understand how the brittlestar manages to build such complex optical systems from scratch. Similar systems are used in technologies called micro lens arrays, which are sets of very small lenses arranged in regular patterns. Micro lens arrays can be used in computers and optical displays, as well as in telecommunication networks.
"This is an excellent example of something we can learn from nature," said Federico Capasso, physical research vice president at Bell Labs."These tiny calcite crystals are nearly perfect optical micro lenses."
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