WITHthe bulging eyes of chameleons do strange things; they rotate in different directions, like periscopes, surveying the surroundings. One eye may be focused on you, and the other on the fleeing insect.
Although scientists have been fascinated by this ability for centuries, the physiological mechanism that makes it possible remains mysterious. Until now.
A team of researchers discovered that chameleons have two spiral optic nerves that operate independently to bring two separate scenes into the reptile's focus. They report their conclusions V Scientific reports document published today.
“Chameleon eyes are like security cameras moving in all directions,” said biologist Juan Daza of Sam Houston State University, the paper's lead author, in his paper. statement. “They move their eyes independently, scanning the environment for prey. And the moment they find prey, their eyes coordinate and move in one direction so they can calculate where to fire their tongue.”
Read more: “Seeing through the eyes of animals»
In the new study, Daza and his colleagues examined the optic nerves of three species of chameleons that differ in body size, evolutionary history and behavior. brown chameleon, Brookesia superciliarisIt is approximately the length of a golf course and lives on the ground or in shrubby vegetation. Bearded dwarf chameleon, Rippeleon brevicaudatusslightly larger, about the size of a crayon, and similar to the habitat. Veiled chameleon Chameleo calyptratethe largest of the group, nearly a foot long and believed to be entirely arboreal. By comparing different species, the researchers hoped to discover what features of the optic nerve structure were common to chameleons.
The high-resolution CT scan confirmed an earlier observation that the chameleon controls each of its eyes independently, but can coordinate eye movements when locking onto a target. Dasa and his team found that this was possible, although it used optic nerves coiled like old-fashioned telephone wires. Tortuosity was observed in all three species. This twisting gave each species a much greater length of optic nerve than normal, allowing them to swing their eyes wildly while the neural tissue was greatly weakened.
When a chameleon's eye turns to look at something, the coiled optic nerve unfolds, giving it the required length. The study authors suggest that without twisting, the nerve is more likely to experience tension due to these radical eye wanders. Studying images of chameleon embryos, the study authors noted that during development, the optic nerves are initially straight, like those of other reptiles, in the egg, but upon hatching they elongate and curl.
This discovery distinguishes chameleons from other animals, which use various adaptations to turn their gaze without straining the optic nerve. For example, owls turn their necks sharply while keeping their eyeballs still. In rats, the optic nerves are elastic, which gives them a little more ability to see.
Chameleons appear to have developed an approach unique in the animal kingdom, making this astounding creature even more of an evolutionary marvel.
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