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.
This lined chiton, whose anterior end is to the right, lives about 50 feet below the water's surface near Whidbey Island, Washington. Credit: Kirt L. Onthank
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 Sönke 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.
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.
Gail Gallessich | EurekAlert!
Immune Defense Without Collateral Damage
23.01.2017 | Universität Basel
The interactome of infected neural cells reveals new therapeutic targets for Zika
23.01.2017 | D'Or Institute for Research and Education
For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.
According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
23.01.2017 | Health and Medicine
23.01.2017 | Physics and Astronomy
23.01.2017 | Process Engineering