Australian mammal demonstrates color vision
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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