Chameleon
jeweled chameleon any of a group of primarily arboreal (tree-dwelling).
Old World lizards best known for their ability to change body colour. Other
characteristics of chameleons include zygodactylous feet (with toes fused into
opposed bundles of two and three), acrodont dentition (with the teeth attached
to the edge of the jaw), eyes that move independently, atrophied venom glands
that produce harmless trace amounts of venom, and a long, slender projectile
tongue. The name has also been applied to the false chameleon, or anole, a New
World lizard of the genus Anolis (family Iguanidae).
Four genera of true chameleons have been described: Bradypodion,
Brookesia, Chamaeleo, and Rhampholeon. Two additional genera (Calumma and
Furcifer) are recognized by some researchers. More than 150 species are
currently known, and additional ones remain to be named. About half of the
species occur only in Madagascar, whereas others occur mostly in sub-Saharan
Africa. Two species occur in Asia; one is native to southern India and Sri
Lanka (Chamaeleo zeylanicus), and the other (the European chameleon, C.
chamaeleon) is found from the Middle East to southern Spain. The most familiar
chameleons belong to the genus Chamaeleo, and these have prehensile tails that
wrap in a coil-like fashion around limbs to maintain balance. In contrast, most
species of pigmy chameleons in the genera Brookesia (Madagascar) and
Rhampholeon (Africa) have short stubby tails that are not prehensile; however,
pigmy chameleons in Bradypodion have longer tails that are prehensile.
The longest chameleon in the world is Parson’s chameleon (Calumma
parsonii), which may grow up to 69.5 cm (about 27 inches) long. On the other
hand, the world’s shortest chameleon, Brookesia micra, has a maximum length of
29 mm (about 1 inch). Most chameleons, however, are 17–25 cm (7–10 inches)
long. The body is laterally compressed, the tail is sometimes curled, and the
bulged eyes move independently of one another. Also, some chameleons possess
helmet-shaped heads.
Jackson’s chameleon [Credit: Art Wolfe—Stone/Getty Images]Some species
have conspicuous head ornamentation that may include as many as three long
horns projecting forward. Such features are either exclusive to or better
developed in males, and at least some of these features are related to
territorial defense. A defending male responds to an invader by expanding the
body, puffing out the throat, and elevating or waving special head flaps. If
this display fails to intimidate the intruder, the defender charges and snaps his
jaws. The differences in appearance between the sexes result from a process
known as sexual selection, in which individual males with extreme ornamentation
have a higher breeding success; they pass on the genes that form the basis for
these features at a faster rate than those individuals lacking ornamentation.
chameleon [Credit: iStockphoto/Thinkstock]Each species is capable of
undergoing a particular range of colour change. The mechanism involves the
dispersal or concentration of pigment granules (melanophore cells) in the cells
that contain them. These cells are under the control of the autonomic nervous
system. Colour change is determined by such environmental factors as light and
temperature as well as by emotions—such as fright and those associated with
victory or defeat in battle with another chameleon. Many chameleons can assume
a green, yellow, cream, or dark brown coloration. Frequently, this occurs with
lighter or darker spots on the background colour of the body. Some of the most
striking colours appear in males during mating. Some achieve colour patterns
that are so vivid and complex that it is hard to imagine that they serve any
natural purpose. It is a popular misconception that the chameleon changes its
colour to match that of the background.
common chameleon The chameleon’s specialized vision and a specialized
tongue-projection system permit the capture of insects and even birds from a
distance. The chameleon’s eyes are very good at detecting and regulating light.
The lens of a chameleon’s eye is capable of focusing extremely rapidly, and it
can enlarge visual images much like a telephoto lens. Although many other
lizards also use the tongue to capture prey, most can expel it only a short
distance. In contrast, chameleons can launch their tongues at great speed to a
distance of more than twice their body length, and they can strike and capture
their prey with great accuracy. The hydrostatic force resulting from rapid
contraction of a ringed accelerator muscle is used to project the tongue toward
the chameleon’s prey; a sticky tongue tip adheres to the victim’s body; and
strong retractor muscles pull the tongue and prey back into the mouth.
Most species are egg layers. Typically, females descend from their shrub
or tree to bury between 2 and 40 eggs in the soil or rotting logs, and
incubation lasts about three months. Some species, such as the large Jackson’s
chameleon (C. jacksonii), bear their young live; however, they do this without
a placenta between the mother and the developing young. All nutrients necessary
for development are contained within the egg itself, which simply develops
within the female’s oviduct minus a shell.
In addition, the Madagascan chameleon, F. labordi, has been widely
acknowledged as the vertebrate with the shortest life span. The eggs of F.
labordi hatch in November, and the young chameleons grow extremely fast; they
mature to adulthood just two months later. After an intense competition for
mates, eggs are laid in February, and the entire adult population perishes.
