Thursday, July 09, 2009

Where are the green mammals?

I was thinking about this a few months back and never figured it out. There are green reptiles, green fish, green birds, green insects, but I don't know of any species of mammal that naturally has any green pigment to its skin or fur. I'm not counting species that have algae living in their hair or something like that, I'm talking about actual green pigment being produced by mammals. For that matter, there's not much in the way of blue or purple for mammals, is there? A prize to anyone who can explain why that might be to my satisfaction.

I was reminded of this by the fact that Katy posted a very blue spider.

12 comments:

Rob said...

Do eyeballs count? That's green/blue pigment, I believe.

Rob said...

Here's a colorful mammal:

http://www.cartage.org.lb/en/themes/arts/photography/equiptechniq/taditionfilm/whatsort/mandrill.jpg

From this post:

http://www.askabiologist.org.uk/punbb/viewtopic.php?id=684

Lykaon said...

Most animals that are brightly colored are so for a reason, usually either to attract mates or warn off predators.

I would guess that mammals have less need for this for various reasons.

Since mammals tend to have remarkably good vision with a huge spectrum of color (especially humans), perhaps bright colors are not as important for mating rituals.

That being said, with make-up and fancy 'girl' colors, one could argue that we still do use bright colors for mating; they just aren't inherent to our species.

It could have a lot do with mammalian diets as well. That can have an effect on pigment.

Humans, at least, have no predators and thus don't need bright colors to scare them off. That's no so for small mammals, however.

Interestingly, mammals tend to camouflage more than not.

Those are just random thoughts I had. Nothing official or anything.

Just Katy said...

From my understanding color vision is fairly poor in most mammals - almost nonexistent. They rely on other sense for communication - mainly scent which is why a lot of mammals are really stinky and should never have been introduced as pets for small children.
I read somewhere that some zoologist believe that most mammilian ancestors were nocturnal or lived under ground and that's why they were able to survive the event (asteroid, cooling period) that killed off the dinosaurs.
Some mammals have a little bit more ability but only humans and the higher apes are trichromates seeing a full spectrum of color. From wikipedia:

Perception of color is achieved in mammals through color receptors containing pigments with different spectral sensitivities. In most primates closely related to humans there are three types of color receptors (known as cone cells). This confers trichromatic color vision, so these primates, like humans, are known as trichromats. Many other primates and other mammals are dichromats, and many mammals have little or no color vision.

So if you want a mammal with some color I think the best option is the Mandril. No green but a very lovely shade of blue on the male's face.

And it's fake but the sloth's of S America are known to be green but it's due to the moss growing in their fur which they use as camo.

My favorite colored mammal is the red panda whose coat is a lustrous mix of oranges reds and purples. Yes, purple on the lower part of the body. This purple shade is hard to see in photos but stunning real life.

Just Katy said...

My point about mammal ancestors being nocturnal or living underground is that eyesight is not too helpful in low light or no light settings.

Just Katy said...

Sorry to junk up the comment section but mandrill has two ls.

Lykaon said...

Nothing like misinformation to get a conversation going.

Okay, so perhaps the color thing is quite the opposite.

If mammals do not see a wide spectrum of color, and are otherwise only minimally impacted by such things then there would be no reason to selectively mutate such an ability for mating.

Though I don't know the facts (a grievous sin for posting on Dave's blog), I think it is a valid hypothesis that there are not brightly colored mammals because there was never an evolutionary need to develop brightly colored features.

As to why exactly there was never a need, I am not educated enough to say for certain but I imagine it has a lot to do with how mammals eat, live, and mate.

On a different topic, there are dogs that are said to be 'blue', though they look more gray to me.

dave said...

So, mandrills being a primate and having color vision does fit with the whole 'lively colors are for mating and that's why nocturnal/colorblind mammals don't need them' hypothesis. I'm rather intrigued they didn't develop as camouflage, but again, I guess only diurnal creatures need that - for example, most reptiles are diurnal because they need that sunlight to heat up their bodies.

I'm gonna award this one to Katy I think. It's true Rob mentioned the URL of a site with some answers, and Josh had some interesting thoughts on human mating, but Katy took the time for a succinct answer (while also contradicting Josh's view of mammal vision, which by itself is prizeworthy).

Therefore, Katy, email me your address and I'll send you a book of my choosing. Eventually.

Just Katy said...

Hurray!! I don't know your email address so I can't email you mine. So you and the whole world can get ahold of me at greenfaucet at yahoo.

Sorry about the double sloth mention. I did read that but in the excitement of commenting I didn't do a good job at editing my stream of conscious thoughts.

I'm still racking my brain for a green mammal. Porcupines sometimes look a little greenish but not really...There's a tibetan blue bear but it's really just grey. I'm also curious why mammals never evolved green pigment - it would make excellent camo. And I would also really like it if some animal somewhere would figure out how to photosynthesize - wouldn't that be convenient? And does anyone know anything about the actual chemical make up of the pigments? I know botanically green yellows and whites (flowers) are much more common than blues and purples. Seems like plants and animals have the opposite color schemes.

I'm really interested in mammal evolution right now so if you can find a book about the Eocene period I would be very impressed. Everybody focuses on the dinosaurs but I think the ancient mammals are a lot more interesting.

richintheory said...
This comment has been removed by the author.
Rich said...

from http://www.madsci.org/posts/archives/2003-09/1064503150.Ev.r.html

What at first appeared to be a
pretty straightforward answer has turned out to be quite complex. The simple answer was going to be: because the evolution of fur made the pigmentation of the skin irrelevant, such that the abilities to produce some of the ancestral pigments were lost to the mammals. This is mostly true, but the exceptions have proven to be as interesting as the answer itself.

In most vertebrates, color, or pigmentation, is produced by special pigment cells called chromatophores (chromato means "color"; phore means "producer") that lie between the inner (dermis) and outer (epidermis) layers of skin. In fish, amphibians, and reptiles these chromatophores come in three flavors: melanophores full of melanins, which are brown/black; xanthophores full of pteridines and carotenoids, which are yellow/red; and iridophores with special "reflecting platelets" that can be silvery to iridescent or complement the other pigments to produce any number of other colors. [The first two references at the bottom of the page give excellent descriptions of the roles of each chromatophore in the pigmentation of frogs and fish, respectively.]

In mammalian skin and hair, there is only one type of chromatophore, the melanophore, which is instead called the melanocyte. With only the one source of pigments for coat color, mammalian have evolved some interesting tricks to extend the spectrum of available colors. First, melanocytes can produce two distinct pigments: eumelanin, which is the traditional brown/black; and pheomelanin, which is yellow/red. Second, melanocytes deposit their pigments into the cells of growing hairs and can cycle through different pigmentation programs, such that a single hair can have stripes, as in the agouti coat color of many mammals. Third, the almost crystalline nature of the keratin arrangements in mammalian hair give fur excellent light-scattering properties. Altogether, these traits fill most of the gaps created by the loss of the other two chromatophores, such that there are white polar bears, yellow cats, red pandas, and green monkeys! (Well, they're not really green, in the way that you mean: they're more olive drab in an agouti sort of way.)

So, the summary would be: as early mammals developed thicker coats of hair, the mammalian chromatoblasts lost the ability to differentiate into xanthophores or iridophores and the surviving melanocytes (nee –phores) were left to make up the difference with their limited repertoire of colors to choose from – hence, no green. I said this would be the summary, because of one particular wrench that requires reassessing the list of available colors: many mammals have brilliantly colored eyes, using the same cells and pigments to color the iris that are used to color the skin and hair. [Discussed in the last reference below.] So, mammals can produce green colorations, but only in their eyes, apparently because the adaptive or courtship value of eye coloration was sufficiently distinct from that of coat color for each to have evolved separately, though both rely on the same cellular palette.



Ichikawa Y, Ohtani H, and Miura I (2001), "The yellow mutation in the frog Rana rugosa: pigment organelle deformities in the three types of chromatophore," Pigment Cell Res. 14(4):283-288

Quigley IK and Parichy DM (2002), "Pigment pattern formation in zebrafish: a model for developmental genetics and the evolution of form," Microsc Res Tech. 58(6):442-455

Oliphant LW, Hudon J, and Bagnara JT (1992), "Pigment cell refugia in homeotherms--the unique evolutionary position of the iris," Pigment Cell Res. 5(6):367-371

Just Katy said...

That is an awesome explanation! I can't wait to read the sources.