Science Questions

How and why do chameleons change colour?

Sat, 8th May 2010

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Question

Jordan Brinkman asked:

I've always thought, like many of my students, that chameleons change colour in response to their environment. †However, after doing some research it seems they change colour based on temperature, light intensity, and mood. †If this is true how does the colour change always seem to match that of their environment? †Could you explain how this process works at a molecular level and how this produces the change in colour?

Answer

Itís natureís example of Joseph and his Technicolour Dream Coat, the chameleon.  They're just phenomenal. 

There is this myth that chameleons change Cape Chameleoncolour to blend in with their surroundings, but this is actually not true.  Most of the reason chameleons change colour is as a signal, a visual signal of mood and aggression, territory and mating behaviour.

The way that chameleons actually do this is really molecular Ė they're molecular masterminds, really.  If you look at the skin of a chameleon, you find that they have several layers of specialised cells called chromatophores and these are cells that can change colour.  On the outer surface of the chameleon, the skin is transparent and just below that is the first layer of these cells, and they contain various pigments.  These are xanthophores, containing particular specialised pigments that have a yellow colour.  Beneath that are pigment cells which are called erythrophores which have a red colour in them.  Beneath that, another layer of cells called iridiphores have a blue coloured pigment called guanine, which is actually also used in making DNA.  And underneath that is another layer of cells called melanophores which have a brown pigment Ė melanin Ė in them. 

Now, how does the chameleon change colour?  Well those chromatophores are wired up to the nervous system.  They are also sensitive to chemicals that are washing around in the blood stream of the chameleon.  What happens is that the colours are locked away in tiny vesicles, little sacs inside the cells that keep them in one place, so the cells don't look coloured.  But when a signal comes in from the nervous system or from the blood stream, the granules or vesicles can discharge, allowing the colour to spread out across the cell, and this alters the colour of the cell.  Itís rather like giving the cell a coat of paint.  By varying the relative amount of activity of the different chromatophores in different layers of the skin, itís like mixing different paints together.  So if you mix red and yellow, you get orange for example, and this is how chameleons do this.  They mix different contributions of these chromatophores.  Itís a bit like on your television screen.  When you mix different colours together on the screen to get the colour that the eye ultimately perceives and so, thatís how the chameleon changes colour, and usually does so to convey mood.

So a calm chameleon is a pale greeny colour.  When it gets angry, it might go bright yellow, and when it wants to mate, it basically turns on every possible colour it can which shows that itís in the mood.  This is not unique to chameleons.  Other animals also have these chromatophores. Cuttlefish are another very elegant example of how this works.  So itís not so much to do with camouflage.  Itís more to do with communication.

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Jordan Brinkman asked the Naked Scientists: Hello All, First, I just want to say I'm a huge fan of the podcast, you guys are fantastic. † I'm a high school biology teacher in Warrensburg, Missouri and I had a student ask me an interesting question: How and why do chameleons change colour? † I've always thought, like many of my students, that chameleons change colour in response to their environment. †However, after doing some research it seems they change colour based on temperature, light intensity, and mood. † If this is true how does the colour change always seem to match that of their environment? †Could you explain how this process works at a molecular level and how this produces the change in colour?†† You're all doing a great job, keep up the good work! Sincerely, Jordan Brinkman What do you think? Jordan Brinkman , Wed, 5th May 2010

http://www.youtube.com/watch?v=g14ARUfF6EI&feature=related @ 6:38 RD, Sun, 10th Oct 2010

Unfortunately QI can sometimes get it wrong - or at least partially wrong.  Although most changes are to do with display and stress, it is also the case that they change colour to camouflage themselves
http://www.newscientist.com/article/dn13944-chameleons-finetune-camouflage-to-predators-vision.html imatfaal, Tue, 12th Oct 2010

Most chameleons change between green, brown and gray - their surroundings are usually the same colors. Each chameleon species has its own color range. They can't just turn any color. Chameleons can change their color because of a very complex cell system. Beneath it's transparent skin are several cell layers which contain pigments. We also have pigments which cause our skin to darken in the sun. By opening and closing cells called melanophores, chameleons change their skin color. The cells direct sun to specific pigments which reflects the light back in different colors.

hunter8br, Thu, 11th Nov 2010

Cool Muse, Mon, 16th Dec 2013

You guys better do a little more research!! I put a green pet chameleon on my back deck, and within a few minutes time, he had changed color to perfectly match the redwood stain of the deck !! A very unique color since it's not a natural color, but the color of the woodstain -- almost couldn't see him !! Dan, Sat, 8th Feb 2014

Youir article is plain wrong. They do change colour depending on the environment. There are videos showing this. They change to blend in to the colour around them. john, Thu, 25th Sep 2014

Yes, could we have a comment on this apparent ability chameleons have to match nearby colours? Are the youtube videos fakes? And if they can do that where does the signal come from to change? Presumably from their eyes? Or can they change colour even if their eyes are covered? Or is all that just a myth? pigsnarl, Tue, 30th Sep 2014

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