Posted on 03/28/2005 8:43:41 AM PST by GreenFreeper
Marsupials not colour-blind after all Catriona Purcell ABC Science Online Monday, 28 March 2005
This little creature, called a quokka, is helping to overturn long-standing beliefs about marsupial vision (Image: Catherine Arrese/Nature)
Australian marsupials can see in full colour, new research has found, making them the only other mammals apart from primates to do so.
A team led by Dr Catherine Arrese from the University of Western Australia in Perth reports its findings in the Proceedings of the Royal Society B, a journal of the UK's Royal Society.
Most people think marsupials lack colour vision, says Arrese, but her team's investigation of Australian quokkas (Setonix brachyurus) and quendas (Isoodon obesulus) have found otherwise.
They looked at cone cells at the top of the retina and the rear of the animals' eyes and found three distinct cone types that enable full colour vision.
Arrese says marsupials, along with other mammals including dogs, cats and horses, were previously thought to have only two types of cone cells which meant they could not detect several colours including ultraviolet, blues or reds.
But she has found short wavelength sensitive (SWS) cone cells that pick up ultraviolet or blue light; medium wavelength sensitive (MWS) cells that pick up colours along the middle of the light spectrum; and long wavelength sensitive (LWS) cells that pick up reds.
Findings apply to all marsupials
The new study supports Arrese's previous findings the fat-tailed dunnart (Sminthopsis crassicaudata) and honey possum (Tarsipes rostratus), which are distant marsupial relatives of the quokka and quenda, also see in full colour.
She expects the most recent findings will convince anyone who was sceptical that her earlier findings applied to all marsupials.
"If a characteristic appears in two groups of distantly-related species of marsupials then it suggests it is across the species," says Arrese.
She says the next step is to conduct behavioural studies to determine if marsupials actually use colour vision to survive.
"At present we know they have the potential to see colour but we still have to learn if they use it," says Arrese. "I would assume they would, as there are plenty of cones and they are not just fading out because they aren't used."
Evolution of human colour vision
Aresse says reptiles and birds have highly developed colour vision with four classes of cone cells including SWS1, SWS2, MWS and LWS.
The discovery in marsupials is, she says, a step forward in understanding the evolution of colour vision in humans.
Humans also have three types of cone cells but they differ to those found in marsupials.
"About 45 million years ago humans appear to have lost two types of cone cells found in reptiles but then developed and re-evolved with a third type of cell that is long and medium wavelength sensitive and picks up reds and greens," Aresse says.
ping
So your saying you stopped?
;)
Are you really green and does green really exist?
Ironically enough, I'm partially color-blind. I'm a few cones short and have difficultly differentiating between certain shades of green- some greens look gray and some look brown. Never noticed until I was made fun of as a kid for painting a donkey green when I thought it was gray.
Humans were around 45 million years ago?
Reptiles and birds have highly developed color vision, and so did "humans" a long time ago. I guess it's a useful trait.
But then, humans lost some of that ability. I guess color vision stopped being so useful.
But then, humans re-evolved color vision, I guess they thought better about their decision to dump that skill.
And this supposed to be a sensible theory? The saying "If it works, get rid of it, you can always re-evolve it later" doesn't cut it for me.
LOL, apparently I also have Deuteranopia as well. I can see the 12 and the 3 in the last circle and that's it.
Thanks but it is decidedly short on the facts.
It did not for instance, report any findings on the skinny tailed Dunnart. One now wonders if color vision could correleate to species success and thus the fatter tail.
There are several factors involved in evolution, one of which is change in the frequency of alleles. There are many varieties of color vision among current humans, any one of which could become widespread if were favored by selection.
...the fat-tailed dunnart....
***
Jeez! I swear! Why does Teddy Kennedy always get dragged into these posts?
This removes the last barrier to holding marsupials responsible for obeying traffic lights.
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I wonder if possums play color-blind as well as playing dead.
Ludwig von Drake once demonstrated color blindness in dogs by waving a plaid-colored steak in front of some dogs, who went after it eagerly.
So, what you're telling me is that, according to the theory, the theory is correct?
Deuteranopia is a form of red-green color blindness. My son is red-green color blind. It's a bit of a nusance, since he is an architect and photographer.
Fortunately, digital cameras have white balance settings that make color correction unnecessary for realistic presentations.
For example, I do not have that 3rd type of cone(well i have a few) yet I still see in color. Apparently I am evolutionarily inferior.
I imagine he means mammals lost the cone cells 45 million years ago and humans got them back somewhere down the road (since there wasn't any species around that was even remotely human 45 million years ago).
Humans without color vision were sought out during WWII, because they could see through enemy camouflage.
Color vision is distracting. That is why when a director desires that his audience pays attention to light and shadow, he will film, if not in black and white, at least in reduced color levels. Lord of the Rings was filmed in some sequences in reduced color level, with, I am told, good effect.
The point is there are advantages and disadvantages with color vision. If it is an advantage, the species may flourish in good times, or survive in bad times, passing the trait along with others to its progeny. If it is less of an advantage in bad times, the species may suffer, or even go extinct.
What is an advantage at one time, may be a disadvantage at other times.
And the animal's decision has nothing to do with it. Nor does the decision of the IPU (invisible pink unicorn) or any other deity.
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