Fifteen shades of photoreceptor in a butterfly's eye

Date: March 8, 2016

Source: Frontiers

The eyes of an Australasian butterfly contain a record fifteen classes of light-detecting photoreceptors, six more than any other insect and far more than necessary for color vision.

When researchers studied the eyes of Common Bluebottles, a species of swallowtail butterfly from Australasia, they were in for a surprise. These butterflies have large eyes and use their blue-green iridescent wings for visual communication -- evidence that their vision must be excellent. Even so, no-one expected to find that Common Bluebottles (Graphium sarpedon) have at least 15 different classes of "photoreceptors" -- light-detecting cells comparable to the rods and cones in the human eye. Previously, no insect was known to have more than nine.

"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 Kentaro Arikawa, Professor of Biology at Sokendai (the Graduate University for Advanced Studies), Hayama, Japan and lead author of the study.

Have multiple classes of photoreceptors is indispensable for seeing color. Each class is stimulated by light of some wavelengths, and less or not at all by other wavelengths. By comparing information received from the different photoreceptor classes, the brain is able to distinguish colors.

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