CHRISTOPHER ANDERSON, POSTDOC ASSOCIATE, BROWN UNIVERSITY, ECOLOGY AND EVOLUTIONARY BIOLOGY: With their independently rotating eyes, color change abilities, their pincher like feet, their long tongue that they project out of their mouth, and their slow deliberate movements, chameleons are animals that most people would regard as charismatic.
One of the centers of chameleon diversity is Madagascar. And of the 202 chameleon species that are currently described to science, 42 percent occur on Madagascar.
One of the old theories as to why chameleons change color is that they were changing color to match their background. But what we now know is that it’s actually a communication strategy. Male-male combat will elicit some of the most impressive colorations from males.
From females on the other hand, if a female is gravid (or she has eggs and is not interested in breeding) if a male starts to try and court her she will display some very intense, vibrant colorations to let the male know that she’s not interested.
In 2015 scientists have discovered that the superficial layer of chameleon skin has pigments in it and under that there are cells with small guanine crystals. Chameleons change color by actively tuning the spacing between these guanine crystals. And what that does is it changes the wavelength of light that is reflected off of those crystals and thereby changes the hue or the color of the chameleons.
Now chameleons have always been considered a master of camouflage and some of that is actually behavioral. When chameleons are moving in the branches or moving along the ground they do a very characteristic back and forth motion. And what they’re actually doing is mimicking a leaf or branch in the wind and trying to break up a typical movement pattern of an animal running from a predator.
The chameleon tongue is actually a highly complex array of bone, elastic elements and muscle. Chameleons can project their tongues up to two body lengths from their mouth. Now this is done at speeds of about 5.8 meters per second or about 13 mph.
Tongue projection in chameleons is similar in a lot of ways to a bow and arrow. Before the tongue is actually launched, or the arrow, muscle action loads elastic elements. And so in a bow and arrow that’s when the arm actually pulls the bow back. Tongue launch is initiated by the recoil of those elastic elements that were loaded by the muscle action or the release of the bow in the bow and arrow model. And it’s the recoil of those elastic tissues, or that bow, that causes that launch of the tongue or the arrow in the bow and arrow example.
Thirty-six percent of chameleon species are threatened with extinction. There are nine species which are regarded as critically endangered and 37 species that are regarded as endangered.
The main threats to chameleons in the wild is actually habitat alteration and deforestation. Because some chameleons are found only in a specific type of habitat on a single mountain this makes them range restricted. But when that range restriction is combined with other pressures on their habitat, a lot of these species become endangered.
Chameleons have fascinated scientists and naturalists for centuries. And it’s something that we’re still learning a lot about.
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