Why color-changing animals alter their appearance
Long ago I had a pet veiled chameleon. I’d read up on chameleons, so I understood the limits of the lizard’s color-changing abilities. For someone who expects a lizard that mirrors its environment perfectly, chameleons can be disappointing. In chameleons and other lizards, camouflage is a secondary purpose for color-changing. The primary purpose of color-changing in chameleons is for communication.
Certain patterns or colors can indicate a bad mood or poor health. Other colors or patterns show that a female is gravid other colors that she’s sexually receptive. People experienced in caring for a specific chameleon species can tell a great deal about the animal’s wellbeing from color. Other lizards are similar.
Anoles (Anolis sp.) change their overall body color from greenish to brownish, usually in response to the environment. Male anoles also have brightly-colored dewlaps. These throat pouches become brighter during anole mating season and bright spots appear in the armpits. The males flare their dewlaps in territorial and courtship displays. Along with little mock pushups, the whole affair is quite a show.
Other lizards such as the collared lizard (Crotaphytus collaris), common to the desert of the Colorado Plateau and Sonoran, have bright red patterns that appear on females when gravid and disappear after she’s laid her eggs. Frilled lizards (Chlamydosaurus kingii) of northern Australia and southern New Guinea, change their colors a bit to blend in with their environments.
Lizards have fascinating abilities to change color and communicate a number of different things with skin color but none of them measure up to the pop cultural portrayal of chameleons. Anyone familiar with bird watching knows that bird plumage changes season by season as well as throughout the bird’s growth to full maturity. Since bird’s color changes come from old feathers being replaced by new ones, it doesn’t seem impressive, but it goes beyond human ability. There is one animal with color-changing abilities for nearly perfect camouflage, but it isn’t a reptile or a bird.
The first time I saw an octopus pull itself from one tide pool to another, I almost couldn’t believe my eyes. If I hadn’t seen the animal move, I never would’ve noticed it, even as I was staring directly down at the cephalopod. Not only can an octopus match the color of a rock or reef beneath it, the animal does a very good imitation of the texture as well. Octopi aren’t the only cephalopods with this impressive ability either. Videos of cuttlefish changing their color to blend into different environments aren’t hard to find online. This seemingly magical ability comes from millions of cells all over the cuttlefish’s body.
Interestingly many different animals have some ability to change color. Some frogs and fish and insects can change color like some lizards. One thing all these animals (including cephalopods) have in common is that they’re so-called ‘cold-blooded’ animals or more precisely ectotherms. All these different color-changing animals have one more thing in common; they all have special cells called chromatophores.
Chromatophores are the technical aspect behind the magic of color change. An article in The Conversation breaks down the different types of chromatophores. There are four types of chromatophores, each with their own pigments associated. Erythrophores contain red pigment. xanthophores contain yellow pigment, iridophores are colorless but have reflective stacks of crystals that can generate blues, whites and ultraviolet colors. Finally, melanophores play the most crucial role and contain black pigment.
Melanophores look somewhat like ‘stars’ with sprawling tentacular arms spread over and between the other chromatophores. Changing the shape of melanophores changes the color of the skin. When the melanophores are relaxed in a way to allow the black pigment melanin to be spread evenly, the colors of other chromatophores are obscured. When the black pigment is concentrated in the center of the melanophore, the color changes. Changing the arrangement of iridophores can also change the color.
Basically, changing the shape of the cells, changes the color of the animal. The changes in vertebrates such as lizards aren’t seemingly controlled consciously by the animal but occur from environmental cues. Unsurprisingly, cephalopods with their superior color changing abilities have unique chromatophores.
In cephalopods, the chromatophores are basically sacs of pigment, shaped by muscle contractions of the animal, allowing fast color changes. Beneath these muscle controlled chromatophores lurk iridophores which are basically the same as in vertebrates and leucophores which look white or reflect the color of whatever light is in the environment.
The main chromatophores in cephalopods lie over the iridophores, which appear white or blue when viewed directly but look reddish when viewed from an angle. The leucophores also lie beneath the chromatophores. As the chromatophores are dilated exposing or obscuring the cells beneath change the color dramatically. Iridophores lying beneath the chromatophores also change their angles to enhance camouflage but don’t seem to be controlled actively by the animal but may instead respond (more slowly) to hormones or other stimuli.
Color changes are at the most dramatic in cuttlefish and have even made their way into pop culture in references to cuttlefish DNA in Jurassic World. It’s worth noting that less impressive color changes than cuttlefish, chameleons and even birds occur all the time. Snowshoe hares (Lepus americanus) are known for losing a brown coat of summer fur and replacing it with white fur in the winter to avoid being seen by predators. Rock Ptarmigan (Lagopus muta) do something similar but losing brownish feathers for white ones instead of fur.
Baboons and related apes have color patches that stand out brightly or dully depending on social or sexual status of the individual. Paleness can indicate illness, lack of nutrition or fear in many animals. Even humans change their color as an adaptation to their environment. Not for camouflage, but a tan is simply an adaptation to allow us to survive under normally blistering suns (obviously some of us are better at this than others). Even animals that maintain their color through life have colors or patterns for important reasons. Leopards, tigers and zebras all have spots and stripes for similar purposes: to catch prey or to avoid being prey.
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By Zach Fitzner, Earth.com Contributing Writer
