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Color-Changing Animals

Nearly all animals have evolved with some form of camouflage, and many depend upon such skills for survival. However, only a few animals can change color in a matter of seconds… so how do they do it?
 
The ability to quickly change skin color comes from the presence of specialized cells called chromatophores. These cells are unique to ectotherms (animals that cannot control their own body heat), such as squid, octopuses, cuttlefish, and the notably color-changing chameleon. Humans are endotherms, meaning we generate and control our body’s internal temperature. While this is good news for our survival, it sadly means we do not possess chromatophores, and therefore cannot turn our skin all colors of the rainbow.
 
Chromatophores contain color pigment that can be red, orange, yellow, brown, or black, and they work by stretching out and condensing on the skin. Imagine a clear balloon full of water and red ink- when the balloon is relaxed, the ink is concentrated in the center making the balloon appear dark. If you were to stretch or flatten the balloon out, the ink would spread out and become a much lighter shade (as seen in the image below). Pigmented chromatophores act like millions of little balloons covering the surface of these animals, each one able to adjust for vivid color displays.
 

Beyond chromatophores, some species also have reflective cells to further change their looks. The first kind (iridophores) are made up of colorless crystals/platelets that create iridescent blues, greens, and gold hues by reflecting light, much like the soap bubbles in your sink. To change the color shimmering off the cell, muscles either shift the iridophores so light hits it at slightly different angles, or they contract the overlying chromatophores to reveal the reflective plates.
 
The second kind of reflective cells, prominent in cuttlefish and octopuses, are called leucophores. They allow for the distinct patterns seen in cuttlefish and can be many colors- bright white being common. They reflect light like a mirror does, so if you shine a bright blue light at a leucophore, the cells will appear bright blue as well. Octopuses rely heavily on these cells which provide bright-colored patches and allow them to match their background environment.
 
Since these animals lack vocal language, they have adapted to using visual properties to send signals and communicate with one another. From specific stripes used in cuttlefish mating rituals to flashing blue rings that warn onlookers that the octopus is venomous, chromatophores, iridophores, and leucophores all play important roles in the behavior and survival of unique ectotherms. Plus, it makes for a beautiful show: check out the video below to see an example of a color-changing cuttlefish.
 

 
References
  
Cover photo credit: David Robinson / Coral Reef Image Bank

Cianci, L. (2023). Colour Theory: Understanding and Working with Colour. RMIT Open Press. https://rmit.pressbooks.pub/colourtheory1/chapter/colour-applications-in-chemistry/
 
Mäthger, L. M., Denton, E. J., Marshall, N. J., & Hanlon, R. T. (2008). Mechanisms and behavioural functions of structural coloration in cephalopods. Journal of The Royal Society Interface, 6(S149–S163). https://doi.org/10.1098/rsif.2008.0366.focus
 
Meyer, F. (2013). How octopuses and squids change color. Ocean. Smithsonian National Museum of Natural History. https://ocean.si.edu/ocean-life/invertebrates/how-octopuses-and-squids-change-color
 
Milne, L. J., & Milne, M. J. (1952). How animals change color. Scientific American, 183(3), 64-67. https://www.jstor.org/stable/24950628         
 

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