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I was in an animal behaviour lecture the other day, and there was a discussion about prey crypsis and camoflague techniques and the question was posed, "Why are there no green mammals?". It makes sense that in green environments then it would be in a preys interest to be green and blend in as insetcs do but this is not the case.It was suggested that is because most predators see in black and white and I was wondering if anyone had any other suggestions.
It should be noted that in many cases it is only the small mammals that need protecting, and they are often found in dirt or in leaf litter which is in fact brown. Also, consider that most mammals have poor colour vision, in which green is usually abandoned. The only predators that may pose any threat to mammals through vision are birds of prey, but again they predate small mammals, which hide well against dirt and in leaf litter, and can find shelter under many plants.
In some cases, green mammals are found. However, this is not the result of a pigment but an algae which grows on the fur. A good example is the sloth; http://deoxy.org/gaia/eyefood/sloth.jpg.
Insects are commonly green because their main predators, birds and other insects, can see green. Most insects are sensitive to all colours except red and infrared, and can even see ultraviolet. A number of studies were cited by A. D. Imms FRS in his book 'Insect Natural History', however I haven't personally looked into these.
One of the only poorly camouflaged animals hunted by predators with good colour vision (buzzards and some other large BoP's) is the rabbit. This doesn't seem to make much difference though, as they are already a very successful species (perhaps due to their speed, sense to stay near an entrance to the burrow and frequent breeding) and so there is not much selective pressure to make a green pigment successful within the species. However, it is possible that given time - a lot of time - green fur will present itself.
"Every cell is a triumph of natural selection." Carl Sagan
Obviously some tropical arborial mammals would be better camouflaged if they were green. I think the answer is simply that mammals lack the ability to produce green pigmentation in their fur or hide, or indeed any great range of pigmentation, compared to reptiles or birds. Basically mammals are only black white or brown. The white can be creamy or the brown almost yellow to orangy chestnut, but there are no primary colours in mammal hair. Strangely, skin can produce primaries, especially in monkeys but it is used for sex and aggression, not for camouflage.
What about this hypothesis?:
Mammals don't use green as a cryptical colour because they usually don't stay motionless among green plants at day.
I will explain this. Because they often have a low metabolic rate, small ectotherm animals such as lizards or insects spend a big deal of time motionless or moving slowly, either to escape from predator's view, to sit and wait for their prey an/or when catching solar heat. Hence for them it is a good strategy to have a similart colour to that of their environment: brown for desert, green for grass or tree canopy.
Mammals instead rarely stop moving, except when sleeping. They have high metabolic rates that force them to move and seek food most of the time. It is their movement what visually calls the attention of their potential prey and predators. So they need a disruptive pattern (spots, stripes, etc) that is not easily seen on a moving background (such as vegetation under wind), and one that is usefull in a variety of visual situations as they move in a patchy environment. Besides, most mammals are active mainly at night when colors are useless.
In such case, all the army clothes would be white&black only. If you have similar colour as your background, it's harder to notice you when at place or to target you when moving. That should be pretty useful.
Cis or trans? That's what matters.
Agree with Jack. Why are spot and srtipes more difficult to see when the bearer is moving? Can we get a reference for that?
Please recall, evolution doesn't go through a complex, after-the-fact thinking process. It may well be as simple as potential pathways in mammals to green pigmentation not beng available or relevant pathways not mutable to the end.
Yes, evolution usually works in simple ways, but understanting them is often a complex task.
I didn't think much to write the "green is useless for mammals" theory, just tried to be original in order to set scientific method to work. In my opinion we have not added enough evidence in this thread yet as to support or rule this theory out.
However both hypotesis presented here are not mutually exclusive: mammals may have lost their ability to create green pigmentations as a result of it not being an advantegeous trait for them.
Come on students do think and write.
Sorry, I could'n get this issue out of my mind.
I sought what others have wrote about it and came across this:
http://www.hhmi.org/askascientist/answe ... 5-195.html
One solution may be the size of arboreal mammals, large and even smaller monkeys are not often hunted from above the trees, but from the ground, and when they are in trees they cling to branches for support, not leaves as arthropods might. This might also explain why smaller arboreal mammals, even terrestrial mammals that might inhabit grass do not have a green pigment- they are not often associated with leaves, as they gather food from the support of brown branches and tree trunks- often not substantially smaller then themselves-, from the forest floor which is brown, or from areas that are generally not grassy -the area around a rabbits burrow does not grow grass.
Mating may also play an important role in the lack of green pigmented mammals, such that mammals tend to select mates based on looks. It may be possible that a green mammal, such as a groundhog, may not be "attractive" enough. Just an idea.
baby fawns stay in one place amongst greenery all day with their mothers away. there is no doubt that many mammals would benefit from green colouring. but there is no way they can produce it.
Reptiles and amphibians don't have green pigmentation either. All mammals, birds, reptiles, and amphibians produce the same two types of pigmentation, melanin amd keratin. The reason many birds, reptiles and amphibians appear green is due to a number of factors, usually having to do with optical phenomenon.
The most likely reason why we don't see green mammals (some exceptions exist, to be mentioned shortly) is probably more a consequence of the nature of mammalian skin and body hair than anything else, which apparently doesn't lend itself to the same sort of optical effects.
The fact that most predatory mammals don't see colors, and wouldn't see the green of a green deer anyway (or the greens of the surrounding environment) probably is a factor here also. Evolutionary pressures are often complex and phenotpes often refiect the influence of various selective pressures over long periods of time. If you're looking for a one sentence, "just so" explanation for why there are no green mammals you're likely to be frustrated.
It's worth mentioning also that sexual selection plays a role here. Colorful displays are used to entice mates by many bird species for example.
Having said all that, it should be metioned that there actually are some green mammals. Polar bears, who actually are not pigmented at all, may appear green when they've been exposed to algae. Some treet sloths appear green due to algae contamination.
Green Monkeys are so named because the younger ones usually have patches of greenish fur ans appear to be green under certain lighting conditions. Truth be told however, I've never seen a photo of one that actually looked green.
Probably the most obvious example of 'green mammals' that is oddly overlooked is our own species, homo sapiens. It is not uncommon for southern Europeans, Middle Easterners, or North Africans to have skin tones that appear somewhat 'green' on color (hence the term "olive skin"). Again, however, truth be told, in my experience most 'olive skinned' people don't really look green at all and it's just a word used to describe swarthy caucasians who would be better described as tan or light brown than green. Certain persons of mixed black African and white ancestry sometimes have a complexion that appears to some as 'green' also.
In any event, you can always dye your dog green if the absence of green mammals bothers you so much. Just make sure your dog is cool with it first. I wouldn't try it with a cat.
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