Navigation Links
Eyes of rock let chitons see predators

(Santa Barbara, Calif.) Using eyes made of a calcium carbonate crystal, a simple mollusk may have evolved enough vision to spot potential predators, scientists say.

Daniel Speiser, a postdoctoral fellow in the Department of Ecology Evolution and Marine Biology at UC Santa Barbara, studied mollusks that he collected in the Florida Keys. His research of their vision, performed during his graduate studies at Duke University, resulted in a study published today by Current Biology.

The three-inch-long mollusks, called chitons, have hundreds of eye-like structures with lenses made of aragonite, a type of rock. It's the first time scientists have found an animal that makes eye lenses from aragonite and not the rock's close cousin, calcite.

Scientists discovered the chiton's unique eyes decades ago. But it wasn't clear whether chitons used these eyes to see objects overhead, or simply to sense changes in light. "Turns out they can see objects, though probably not well," said Speiser.

"It's surprising how these creatures make their eyes from rocks," said Snke Johnsen, associate professor of biology at Duke. Most animals make their eyes from cells with proteins and chitin. "But it seems like an easy way to evolve eyes, by using what you've already got," he said. Chitons also make their shells from aragonite.

Johnsen and Speiser studied West Indian fuzzy chitons, or Acanthopleura granulata, which have flat shells made of eight separate plates. Hundreds of tiny lenses on the surface of the plates cover clusters of light-sensitive cells beneath.

To test the creature's vision, Speiser placed individual chitons on a slate slab. When left undisturbed, they lift part of their armored, oval-shaped body to breathe. At this point, Speiser showed them either a black disk ranging from .35 centimeters to 10 centimeters in diameter or a corresponding gray slide that blocked the same amount of light. The disk or slide appeared 20 centimeters above the chitons.

When shown the gray screens, the chitons did not respond. But they clamped down when shown a black disk three centimeters or larger in diameter. That would be the equivalent of humans looking in the sky and seeing a disk the diameter of 20 moons, making human vision about a thousand times sharper than chiton vision, Johnsen said.

Because the chitons responded to the larger disks and not the gray slides, they seem to be seeing the disk and not simply responding to a change in light, said University of Sussex biologist Michael Land, an expert on animal vision who was not involved in the research. It's not yet clear if they respond only to the removal of light by the disk as opposed to added light.

Land also said it's not likely that the chitons' eyes were part of the evolutionary route to human eyes.

Chitons are an ancient, primitive species that first appeared on Earth more than 500 million years ago. But the oldest chitons with eyes only began to appear in the fossil record in the last 25 million years, making their eyes among the most recent to evolve in animals. Speiser said chitons probably evolved to have eyes with lenses so they could see their predators and defend themselves against being eaten.

Speiser and his colleagues also tested whether the chitons' eyes work in both air and water, since some species spend time in both. The experiments made a strong case for the chiton lens being able to focus light differently, depending on whether the animal is above or below water, Land said.

He added that chiton eyes are still an anomaly in the evolution of vision. The retinas are structurally similar to snail and slug retinas. But snail and slug retinas respond to the appearance of light, while chiton retinas may only respond to the removal of light, a difference that might be worth another look, Land said.


Contact: Gail Gallessich
University of California - Santa Barbara

Related biology news :

1. Hind wings help butterflies make swift turns to evade predators, study finds
2. As super-predators, humans reshape their prey at super-natural speeds
3. Sexy or repulsive? Butterfly wings can be both to mates and predators
4. Predators ignore peculiar prey
5. Siberian jays use complex communication to mob predators
6. Venomous sea snakes play heads or tails with their predators
7. Lizards change their diet to avoid predators
8. Move over predators: Plants can control the food chain too -- from the bottom up
9. Return of top predators is key to ecological future
10. Making its predators tremble: Multiple defenses act synergistically in aspen
11. Cycad pest uses small size to hide from predators
Post Your Comments:
Related Image:
Eyes of rock let chitons see predators 
(Date:5/16/2017)... , May 16, 2017   Bridge Patient ... organizations, and MD EMR Systems , an ... partner for GE, have established a partnership to ... product and the GE Centricity™ products, including Centricity ... These new integrations will allow ...
(Date:4/24/2017)... April 24, 2017 Janice Kephart ... with  Identity Strategy Partners, LLP (IdSP) , today ... without President Trump,s March 6, 2017 Executive ... , refugee vetting can be instilled with greater confidence, ... now, all refugee applications are suspended by until ...
(Date:4/18/2017)... 18, 2017  Socionext Inc., a global expert in SoC-based imaging ... server, the M820, which features the company,s hybrid codec technology. A ... Tera Probe, Inc., will be showcased during the upcoming Medtec Japan ... at the Las Vegas Convention Center April ... Click here for ...
Breaking Biology News(10 mins):
(Date:10/12/2017)... New York, NY (PRWEB) , ... October 12, ... ... York Academy of Sciences today announced the three Winners and six Finalists of ... Awards are given annually by the Blavatnik Family Foundation and administered by the ...
(Date:10/12/2017)... ... October 12, 2017 , ... AMRI, ... and biotechnology industries to improve patient outcomes and quality of life, will now ... testing are being attributed to new regulatory requirements for all new drug products, ...
(Date:10/11/2017)... ... October 11, 2017 , ... Personal eye wash is a basic first aid supply for ... time. So which eye do you rinse first if a dangerous substance enters both eyes? ... Eye Wash with its unique dual eye piece. , “Whether its dirt and debris, ...
(Date:10/11/2017)... and LAGUNA HILLS, Calif. , Oct. ... Cancer Research, London (ICR) and University ... SKY92, SkylineDx,s prognostic tool to risk-stratify patients with multiple myeloma ... MUK nine . The University of Leeds ... partly funded by Myeloma UK, and ICR will perform the ...
Breaking Biology Technology: