Why does this butterfly have such spectacular color vision?

A common butterfly species surprised researchers with its unique eyes.

Researchers studying Common Bluebottles butterflies have discovered that the species may have some of the most capable eyes in the animal kingdom. The species of butterfly are known for having big eyes and brightly colored wings, which suggested eyes good enough to allow visual communication. When studies, the eyes revealed more light-detecting cells than have been found in any other type of insect eyes.

The Common Bluebottles butterflies contain 15 photoreceptors, which are comparable to the rods and cones found in human eyes. No insect was previously known to possess more than nine, according to the press release.

But as other animals make due with far fewer, why do these butterflies need such sensitive eyes? It might help give them an edge in survival, according to scientists.

"Butterflies may have a slightly lower visual acuity than ourselves, but in many respects they enjoy a clear advantage over us: they have a very large visual field, a superior ability to pursue fast-moving objects and can even distinguish ultraviolet and polarized light. ” Kentaro Arikawa, professor of biology at the University in Hayama in Japan and lead author of the study, said in the press release.

Having multiple classes of photoreceptors is necessary for seeing color. Typically, each class is used to detect light from a different wavelength. The brain compares the information from the different photoreceptor classes and is about to tell the difference between colors.

Humans typically have just three classes of cones in their eyes, but that enables them to view millions of colors. Many other insects also use only three classes of photoreceptors and manage to have effective color vision. In that regard, the researchers believe the butterfly species is similar.

Dr. Arikawa and his team found the butterfly species only uses four photoreceptor classes to detect color. Physiological, anatomical, and molecular experiments concluded that of the 15 photoreceptor classes, one detected ultraviolet light, one violet light, one blue-green lights, three blue lights, four green lights and five red lights.

The 11 photoreceptor classes that the butterfly species doesn’t use to detect color are likely used to give it an edge in spotting specific stimuli in the environment. They are fine-tuned to detect aspects as specific as fast-moving objects or predators moving against the sky or colorful plans hidden among other terrain.

Similar conclusions on the Asian swallowtail, Papilio xuthus, a distantly related relative to the Common Bluebottle, were drawn from previous studies, according to the press release. But P. xuthus has only six photoreceptors.

"We have studied color vision in many insects for many years, and we knew that the number of photoreceptors varies greatly from species to species. But this discovery of 15 classes in one eye was really stunning," says Arikawa.