Wild Israel: Toy dinosaurs

The chameleons' mastery of camouflage has been proved more remarkable than previously thought.

By DIANA BARSHAW
July 2, 2009 14:12
Wild Israel: Toy dinosaurs

Chameleon 88 248. (photo credit: Diana Barshaw)

 
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Chameleons belong to a family of lizards called the Chamaeleonidae. This family of about 160 species is most famous for its ability to change color, although there are several species of chameleons that lack the ability. However, all chameleons are slow animals that have feet specialized for holding on to narrow branches with three fused toes on one side and two on the other; all have remarkable tongues which are sometimes longer than the length of the animals themselves, and shoot out of their mouth to catch unsuspecting prey on the sticky tip; and all have eyes that can each move independently of each other, giving a 360-degree field of vision and an ability to detect multiple prey or threats. Several years ago, before my son Daniel was a teenager, we were driving home when he yelled, "Look at that toy dinosaur." I saw what looked like a bright green plastic lizard and pulled over to get it. The "toy" lizard was actually a living chameleon swaying from side to side in the middle of the road as if it were having an anxiety attack. Daniel and I stopped the traffic, carefully picked up the chameleon and carried it to a bush across the street. We watched it slowly climb up a branch and suddenly turn brownish. After we turned around for a minute to talk with a passerby, we couldn't find the chameleon anywhere when we looked for it again. Chameleons are slow, so it was surely still there, however it was so well camouflaged that we couldn't distinguish it from the background no matter how hard we looked. THE SPECIES of chameleon we saw on the street in Haifa is the common chameleon (Chamaeleo chamaeleon, "zikit metzuya" in Hebrew.) The swaying motion is meant to simulate the movement of leaves in the wind and is another way that these animals avoid detection by either prey or predators. Each species of chameleon has its own range of colors that are displayed in a characteristic pattern. The Israeli C. chamaeleon's colors range from brown to brilliant green. These colors are made by three layers of pigment cells called chromatophores that reside in the skin. The deepest layer is black, the middle layer is blue and the upper layer is yellow and red. Just as a painter will mix various paints to get the exact hue needed, a chameleon will push certain layers of chromatophore together to get the coloring that it needs. It is clear from watching these lizards that their color change is used for camouflage, both so unsuspecting prey will come within their reach and to avoid becoming prey themselves, but recently the chameleon's mastery of camouflage was shown to be more remarkable than previously thought. A group of scientists led by Devi Stuart-Fox at the University of the Witwatersrand used models of birds and of snakes and a spectrometer to show that dwarf chameleons in South Africa change colors differently and behave differently depending on the predator threatening them. When a bird was the threat, the chameleon carefully positioned itself so that it was hanging underneath the branch and it changed its color to exactly match the environment. When a snake was the predator, the lizards stayed on top of the branch and did not match the environment as closely. The birds hunt from above and the snakes from below, so the positioning behavior is clear, but why the difference in color change? Stuart-Fox speculated that the lizards save energy by not being as exact in their camouflage for snakes because snakes can't see as well as birds. TO CAPTURE prey, the chameleon sways like a leaf on a branch, perfectly camouflaged against its environment, and waits. The chameleon then spots a likely victim, usually a fly or other insect, with one of its eyes, but it is not possible to get depth perception with only one eye, so it then swivels its other eye in the same direction to get the binocular vision necessary to aim properly. Then the tongue is blasted out at the prey as far as one and a half times the body length of the lizard at speeds up to 1,800 kilometers per hour (faster than the speed of sound). Jurriaan H. de Groot and Johan L. van Leeuwen from Leiden University in the Netherlands found that to get such speed requires much more power than can be generated by muscle tissue. So how do these lizards do it? De Groot and van Leeuwen suggest that the tongue is analogous to a catapult. The muscles are used, at a slower rate, to cock the catapult and then a quick-release mechanism allows the stored energy to shoot out the tongue at high speed. Interestingly, one of the important predators of the common chameleon is the common chameleon: They can be cannibals. Tammy Keren-Rotem of Tel Aviv University found that the adults of this species prey on juveniles. Keren-Rotem collected chameleons in the Carmel Nature Reserve and found that juveniles were usually found lower in the bushes and trees than adults. These chameleons were then carefully observed both in the field and in specially designed cages. Keren-Rotem found that one important reason that the young stay lower than the adults was because if they didn't the adults would eat them. Chameleons don't change color only for camouflage, they also use color to communicate with each other. Mariano Cuadrado from the Estacion Biologica de Donana, CSIC in Spain did a series of experiments with the same species we have here in Israel, C. chamaeleon. By observing the behavior of natural and painted females in the field, he showed that females which were ready to mate had a particular color and that males were more likely to attempt mating with such females. Other scientists have shown that some species of chameleons use color change to communicate reproductive status, for dominance displays and to show territoriality. Next time you look at a field of bushes and trees, think of the many chameleons that are waiting patiently for their next meal while hidden in plain sight.

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