Why can some species see more colors?
The color vision of animals
The proverbial keen eye of the eagle and the almost blind mole show how differently the eyesight is developed in vertebrates. But color vision is also not developed in the same way in vertebrates.
The colors animals perceive differ from human color vision - evolution has developed color vision several times independently of one another. The differences lie in the receptors and to which wavelengths they react - in any case, most animals can distinguish colors from one another.
Among mammals, only primates have three color receptors - humans and some monkeys. Dogs and cats, on the other hand, are dichromates with two types of cones.
Why mammals don't see UV light
We now assume that mammals lost the ability to see UV rays at an early stage of their development.
At wavelengths below 500 nm (near the UV range), the electromagnetic radiation potential becomes strong enough to destroy the photopigments (within around 10 years) and turn the lens of the eye yellow. Many birds and insects have UV-sensitive receptors - but these animals also have relatively short lifespans and do not live long enough that the destructive energy of UV waves does not become significant.
Large mammals, on the other hand, live long and collect more UV radiation, so their eyes have to filter out the harmful radiation. The fact that humans and other mammals do not see in the UV range is not a shortcoming of human vision, but a protective function.
Insects, on the other hand, have an extremely short life span and can use this range of wavelengths.
The color vision of insects
Like humans, bees and bumblebees are trichromats with three types of receptors.
However, their maximum sensitivities are 350 nanometers (ultraviolet) in the UV range of the spectrum, 450 nanometers (blue-violet) for blue and 530/580 nanometers for green-yellow. The bee perceives UV light, but not red - these wavelengths appear to them like black.
Evolution has not adapted the bees to the splendor of the colors of the plant world, but, conversely, has adapted the plants to the ability of insects. Because insects developed color vision, the highly saturated colors of the flowers evolved to attract insects.
The bee's color vision is shifted by around 150 nm in the shorter-wave light compared to the human color vision. So the bee does not see red, but some of the ultraviolet light. You can see the blossoms of flowers in completely different colors than humans, because you cannot perceive the red of a poppy blossom, but you can perceive the ultraviolet rays that are reflected by the poppy blossom. Where the yellow flowers of oilseed rape and mustard look exactly the same to us, bees can see the differences, as each type of flower reflects the rays differently.
Bees see the light polarized, which in combination with the time of day of the sun enables them to determine the direction of the compass precisely. When the bee is not moving, it sees relatively poorly with its compound eyes, comparable to a digital camera that has only a few thousand pixels. However, this changes significantly during flight. In this analogy, in contrast to the static image, a film is now running, with many image changes per unit of time. Ultimately, this can - through interpolation - improve the image resolution.
Not all insects have three receptors; there are also bichromatic insects.
One pigment absorbs green-yellow light (550 nm), the other blue-ultraviolet light (
Chickens are tetrachromats with four cone pigments for red (approx. 570 nm), green (approx. 510 nm), blue (approx. 450 nm) and violet (approx. 420 nm). Budgies see into the UV range and can distinguish more shades of blue from one another than a human can.
In addition, many birds have oil droplets embedded in the cones that they can use to expand or narrow the spectral range.
The color vision of the fish
As early as 1913, Karl von Frisch was able to use training techniques to prove that carp-like fish (cyprinids) have a highly developed color vision.
3 cone types with maximum sensitivity of around 450 nm, 530 nm and 620 nm.
In goldfish and carp, ultraviolet cones were detected by microspectrophometry (Whitmore and Bowmaker 1989).
Now, the presence of four types of cones does not have to mean that the creature actually has tetrachromatic color vision. This requires an additional mix of experiments and training.
Christa Neumeyer describes the structure of the training in her paper.
Institute for Zoology, J. Gutenberg University Mainz
Tetrachromatic color vision in goldfish: evidence from color mixture experiments, Aug 1992
So colorful, so colorful: pentachromats
There are butterflies with five color receptors (pantachromats) and the cichlid (as I have read) is not only colorful, but also has 12 color receptors.
Some surprising facts about color vision
Jellyfish do not have a brain, but there are species that have eyes (box jellyfish). The eyes of the sighted medusa can be very sophisticated - in experiments scientists have found that they can also distinguish colors.
"Advanced optics in a jellyfish eye" by Dan-E. Nilsson and colleagues (Lund University), May 2005 in "Nature" Volume 435, pp. 201-205, Doi: 10.1038 / nature03484.
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