Hayama, Japan – Japanese researchers from the Graduate University for Advanced Studies (SOKENDAI) have discovered that a species of swallowtail butterfly from Australasia has at least 15 different classes of light-detecting cells in its eyes, the largest number of different vision cells for any insect.
The findings are detailed in the open-access journal Frontiers in Ecology and Evolution.
Through physiological, anatomical, and molecular experiments researcher found out that this species of the swallowtail butterfly, commonly known as Bluebottles butterflies, have large eyes that use their blue-green iridescent wings for visual communication. This fact indicates that their vision must be excellent.
“We have studied colour 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,” said lead author Kentaro Arikawa, a professor at the SOKENDAI.
Researchers note that further study is needed in order to assign a specific function all of the photoreceptors.
Bluebottles butterfly vs human beings
Humans have four classes of photoreceptors. Three of them, called cones, are for color vision. The other type of photoreceptor, called rods, are specialized for seeing shape, movement and changes in light and dark.
The large compound eyes possessed by butterflies cannot see as clearly as human eyes, but they are better at seeing a wide panorama, fast movement, polarisation and grades of colour.
Akariwa explained that these butterflies may have a slightly lower visual acuity than human beings but in many respects, they enjoy a clear advantage over us as they have a very large visual field, a superior ability to pursue fast-moving objects and can even distinguish ultraviolet and polarised light.
Why do they need 15 Photoreceptor classes?
The study claims that all the photoreceptors are used at the same time, sensing color, brightness, movement and shape.
The findings revealed that Common Bluebottles use only four classes of photoreceptors for routine color vision. The other eleven are used to detect very specific stimuli in the environment, for example, fast-moving objects against the sky or colourful objects hidden among vegetation.
Researchers determined that out of the 15 photoreceptor classes, one is stimulated by ultraviolet light, another by violet light, three stimulated by slightly different blue lights, one by blue-green light, four by green lights, and five by red lights.
Source: Discovery News