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Chameleons

Chameleons

Biology of chameleons

Species of chameleons

Chameleons and people

Resources

Chameleons are small, strange-looking lizards in the family Chamaeleonidae. There are about 180 species and subspecies of chameleons in six genera. The majority of species of chameleon are found in the tropics of Africa and Madagascar, but some species live in southern Spain, Crete, India, and Sri Lanka. Most species of chameleons spend their lives in trees and shrubs, but some occur in herbaceous, grassy vegetation, and a few can be found on the ground.

Biology of chameleons

Most chameleons are green, yellow, or brown colored. However, these animals are famous for their ability to rapidly change the color and pattern of their skin pigmentation among these colors, and almost black or white shades can be achieved. This is done by varying the amount of pigment displayed by specialized cells in the skin, known as chromatophores. This visual behavior is primarily performed in response to changes in temperature, sunlight, and mood, especially when a chameleon is interacting socially with other chameleons. Chameleons may change the color of their skin to blend in better with their surroundings, as a type of opportunistic camouflaging. Although it is often believed that camouflage is the most common reason for the color changes of chameleons, the primary reasons are actually related to the mood or motivation of the animal.

Almost all chameleons are arboreal animals, moving slowly and deliberately in their habitat of trees and shrubs. The often imperceptible movements of these animals, coupled with their usual green or mottled color, makes chameleons difficult to detect among the foliage of their habitat. Chameleons have feet that grip twigs and branches well, with their toes fused in groups of two or three (a zygodactylous arrangement) that oppose each other to confer a strong grip.

The prehensile tail of most chameleons can be wrapped around twigs and other structures to give the animal stability while it is resting or moving around. In some respects, the tail serves as a fifth leg for these animals, because it is so useful for locomotion and securing their grip. The laterally compressed body of chameleons also appears to be an adaptation to a life in the trees, by conferring advantages related to the distribution of body weight, and perhaps in camouflage.

Chameleons have very unusual eyes, which extend rather far from the sides of the head within turret- or cone-like, fused eyelids. The eyes of chameleons can move and focus independently of each other. However, chameleons also have excellent binocularvision, which is necessary for sensing the distance of prey from the animal, so that it can be accurately snared by the long, unfurled tongue.

The tongue of chameleons is very important for the method of feeding. This tongue is very long, and it can be rapidly extended by inflating it with blood. The tongue is accurately and quickly extruded from the mouth to catch prey up to a body length away from the animal. The sticky, club-like tip of the tongue snares the arthropod prey securely. Chameleons commonly feed on insects of all sorts, as well as on spiders, and scorpions.

Like other lizards, chameleons also use their tongue as a sense organ. The tongue is especially useful as a chemosensory organ which detects chemical signals from the air, ground, or food. The chemicals are transported to a sensory organ on the roof of the mouth, which analyzes the chemical signature.

Male chameleons aggressively defend a breeding territory, interacting with other males through drawn-out, ritualized displays. Some species have horn- and crest-like projections from their forehead which are used by the males as visual displays during their territorial disputes, and for jousting, during which the animals push at each other with their horns, until one combatant loses its grip on the branch, and falls to the ground. Most species of chameleons lay eggs, but a few are ovoviviparous, meaning the eggs are retained within the body of the female, where they hatch, so that the young are born as miniature replicas of the adults.

Some populations of chameleons consist entirely or mostly of female animals. This is an unusual trait in animal populations, and it may be indicative of parthenogenesis in these chameleon species, that is, the production of fertile eggs by females that have not mated with a male animal.

Species of chameleons

There are six genera of chameleonsChamaeleo, Brookesia, Bradypodion, Furcifer, Rhampholeon, and Calumma. The genera Chamaeleo and Brookesia are the largest. Species of Chamaeleo occur in Africa, Madagascar, southern Europe, and southern and Southeast Asia. Species of Brookesia occur only

in East and West Africa and on the island of Madagascar.

The European chameleon (Chamaeleo chameleon ) is represented by a number of subspecies in a few places in southern Europe, and much more widely in northern Africa, southern Arabia, and India. The African chameleon (C. africanus ) occurs from West Africa through Somalia and Ethiopia. The common chameleon (C. dilepis ) occurs throughout sub-Saharan Africa.

Some Madagascan and African chameleons have long projections on their snout which are used by male animals during their territorial jousts. Examples of these unusual, horned chameleons are Fischers chameleon (C. fischeri ) and the mountain chameleon (C. montium ). The most spectacular of the horned species is Owens chameleon (C. oweni ), which has three long, Triceratops -like horns. This species is only found in the lowlands of Cameroon.

Unlike Chamaeleo, species of Brookesia chameleons do not have a prehensile tail, and they do not undergo marked color changes. Examples of these stump-tailed chameleons are Brookesia superciliaris, B. stumpfi, and B. tuberculata, all found on Madagascar and several neighboring islands. Brookesia spectrum and B. platyceps occurs throughout sub-Saharan Africa.

Chameleons and people

In some regions local people have developed a fear of these unusual, bizarre-looking lizards, believing them to be poisonous or deadly in some other way. In other places, chameleons are believed to have medicinal value, and are sold dried for use in folk medicine.

Chameleons are striking and interesting animals, and they are sometimes kept as pets. Some chameleons are also sold internationally in the pet trade. However, chameleons are rather finicky creatures, and they usually do not survive very long in captivity. Not many people have the zoological skills needed to successfully keep chameleons alive.

As with so many other types of wildlife, the greatest threat to populations of chameleons is through the loss of their natural habitat. Most chameleon species do not adapt well to habitats that are intensively

KEY TERMS

Ovoviviparous The retention of fertilized eggs within the reproductive tract of a female animal, where the eggs hatch, and the young animals are later born as small replicas of the adult animals.

Parthenogenesis The production of fertile, diploid eggs by female animals that have not mated with a male. In lizards, this trait is generally accompanied by all-female populations or species.

managed by humans. As a result, the populations of chameleons generally decline markedly when their natural habitats are converted to agricultural or residential land uses. Currently seven species of chameleons are listed as vulnerable, endangered, or critically endangered by the World Conservation Union (IUCN).

See also Anoles.

Resources

BOOKS

Halliday, T.R., and K. Adler. The New Encyclopedia of Reptiles and Amphibians. New York: Oxford University Press, 2002.

Halliday, T.R., M. Oshea, and J. Metcalf. Smithsonian Handbooks: Reptiles and Amphibians. New York: DK Publishing,2002.

Necas, P. Chameleons: Natures Hidden Jewels. Malabar, FL: Krieger, 1999.

Bill Freedman

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