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Australian mammal demonstrates color vision

BioPhotonics
Apr 2006
Trichromatic color vision has been thought to be unique to primates among mammals, but researchers have recently discovered that the fat-tailed dunnart, a marsupial in Australia, has functional trichromatic color vision as well.

As reported in the March 21 issue of Current Biology, researchers from the University of Western Australia in Crawley and at Gutenberg University in Mainz, Germany, first trained three young dunnarts to detect a monochromatic light of a certain wavelength. Once the mammals responded to the training wavelength by running toward it and pausing in front of it, their choice was tested against another wavelength.

When choice frequency exceeded 80 percent, the researchers combined two wavelengths and tested the mixture against the initial training wavelength. Initial experiments showed that dunnarts discriminated between wavelengths ranging from 525 to 620 nm with 80 to 100 percent accuracy, providing an initial indication of trichromacy.

If three cones were contributing to color vision, any spectral stimulus could be matched with a specific mixture of three primary wavelengths. Thus, the researchers tried matching white tungsten light with a mixture of 360-, 450- and 620-nm light. If dunnarts trained to move toward the white light could not detect the difference between it and the mixture of wavelengths, it would show that they had trichromatic vision.

The results of the experiments showed that the dunnarts were trichromatic but in a different way from other mammals, in that one of the types of cones they have is sensitive to the UV region. The researchers believe that further testing with a wider range of species will help determine whether trichromacy is the general color system of Australian marsupials.


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