How do Animals Change Colour?

Wouldn’t it be great if every time we get embarrassed, we could just disappear?

Well, there are a variety of animals that actually can! Well, maybe not quite disappear but blend into their background by changing colour. Animals may change colour in order to camouflage themselves for protection or to communicate with each other, but do you know exactly how it all works?

The one animal that is especially famous for extravagant colour changing is the chameleon. There has been new research completed on this topic in the University of Geneva, by a group of biologists and physicists. It was proven that the chameleon has a layer of skin cells containing tiny crystals that are evenly spaced out. I’m not talking Swarovski crystals or those you’d find in H.Samuels, but little things called nanocrystals.

To put them into perspective, a human hair is between 60,000 and 80,000nm wide and one of these nanocrystals is around 100nm wide - basically, they are very small! The space between the crystals determines what colour of light can be reflected and the chameleon can change colour from one to another by changing the spacing between these tiny crystals.

But, how can the spacing between the crystals can be altered? Well, it’s actually very simple: the spacing of the crystals is altered when the mood of the chameleon changes. So, when a chameleon is calm, the crystals are close together and blue light is reflected, but when excited the crystals loosen and become further apart, causing yellow or red to be reflected. So when combative males strut their colourful stuff, they are changing the spacing between their crystals. I think we should all be very grateful that this doesn’t happen to us!

Not only can chameleons change from colour to colour, they can also change to different shades of the same colour - not quite fifty shades, though! This is done when melanin moves in and out of cells. Melanin is the pigment in our skin that is responsible for giving us a tan, so a person with darker skin will have more melanin than someone with fair skin.

Not all animals that change colour do it in the same way as the chameleon. Another colour changing critter is the cuttlefish, sometimes known as the “chameleon of the sea”. They have cells containing chromatophores, which are the things that contain the colour pigments. A cuttlefish changes colour when the layer of muscle surrounding its chromatophores constricts and expands. When the muscle constricts, the pigment is moved to the top of the cell, like squeezing toothpaste out of a tube.

Credit: Mentaldstruction

The cuttlefish can actually control the contraction and relaxation of the muscles around individual chromatophores, thereby controlling what colours are expressed on their skin. This means that, unlike chameleons, the cuttlefish can change colour when it moves into different surroundings, rather than their colours being controlled by their mood.

Cuttlefish also use their colour changing ability to hypnotise their next meal! They put on a miraculous show in order to make their prey more vulnerable to their attacks. The octopus and the squid also contain chromatophores and use the same mechanism as the cuttlefish in order to change colour.

Let me just go back to the beginning where I mentioned getting embarrassed. As humans, this is our way of changing colour. Okay, it isn’t as cool as being able to change colour to blue or pink with polka dots, but when we get embarrassed, we blush. Embarrassment leads to adrenaline being released, which causes our blood vessels to open wider so more blood will flow through them. Blushing is caused when there is a rush of blood to the face, and some parts of our face will have larger blood vessels closer to the surface of our skin, which is why our cheeks turn red. The biological purpose of blushing is still not clear.

These colourful creatures are actually a lot smarter than we give them credit for! So, if you ever come across an animal changing colour, you can impress your friends by telling them exactly how it works!

#Biology #Colour #EllenMarieSmith

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