Chameleons

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Biography

Chameleons (family Chamaeleonidae) are a distinctive and highly specialized clade of lizard s. They are distinguished by their zygodactyl ous feet, their separately mobile and stereoscopic vision|stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, their swaying gait, the possession by many of a prehensile tail, crests or horns on their distinctively shaped heads, and the ability of some to change color. Colors include pink, blue, red, orange, turquoise, yellow, and green. Uniquely adapted for climbing and visual hunting, the approximately 160 species of chameleon range from Africa , Madagascar , Spain and Portugal , across south Asia , to Sri Lanka , have been Introduced species|introduced to Hawaii , California and Florida , and are found in warm habitats that vary from rain forest to desert conditions. Chameleons are often kept as household pets.

Etymology

The English word chameleon (also chamaeleon ) derives from Latin chamaeleo , a borrowing of the Ancient Greek ?aµa????? ( khamailéon ), a compound (linguistics)|compound of ?aµa? ( khamaí ) "on the ground" and ???? ( léon ) "lion". The Greek word is a calque translating the Akkadian language|Akkadian neš qaqqari , "ground lion".

Evolution

The oldest known chameleon is Anqingosaurus|Anqingosaurus brevicephalus from the Middle Paleocene (about 58.7-61.7 mya (unit)|mya ) of China.

Other chameleon fossils include Chamaeleo caroliquarti from the Lower Miocene (about 13-23 mya (unit)|mya ) of the Czech Republic and Germany, and Chamaeleo intermedius from the Upper Miocene (about 5-13 mya (unit)|mya ) of Kenya.

The chameleons are probably far older than that, perhaps sharing a common ancestor with Iguanidae|iguanids and agamids more than 100 mya (unit)|mya (agamids being more closely related). Since fossils have been found in Africa, Europe and Asia, chameleons were certainly once more widespread than they are today. Although nearly half of all chameleon species today are found in Madagascar, this offers no basis for speculation that chameleons might originate from there. Monophyly of the family is supported by several studies.

Description

Chameleons vary greatly in size and body structure, with maximum total length varying from in male Brookesia micra (one of the world's Smallest organisms#Smallest reptile|smallest reptiles ) to in the male Malagasy Giant Chameleon|Furcifer oustaleti . http://www.dailymail.co.uk/sciencetech/article-2101040/Discovered-The-mini-meleon-smallest-reptiles-planet.html? ITO=1490 Many have head or facial ornamentation, such as nasal protrusions, or horn-like projections in the case of Jackson's Chameleon| Trioceros jacksonii , or large crests on top of their head, like Veiled Chameleon|Chamaeleo calyptratus . Many species are sexual dimorphism|sexually dimorphic , and males are typically much more ornamented than the female chameleons.

Typical sizes of species of chameleon commonly kept as pets are:

Species' Scientific Name !! Species' Common Name !! Length (Male) !! Length (Female) !! Color !! Lifespan (Years)
Chamaeleo calyptratus
Trioceros jacksonii
Furcifer pardalis
Rieppeleon brevicaudatus
Rhampholeon spectrum
Rhampholeon temporalis

The feet of chameleons are highly adapted to arboreal locomotion , though species such as Chamaeleo namaquensis , that have secondarily adopted a terrestrial habit, have retained the same foot morphology with little modification. On each foot there are five clearly distinguished toes that are grouped into two fascicles. The toes in each fascicle are bound into a flattened group of either two three, giving each foot a tongs -like appearance. On the front feet the outer, Anatomical terms of location|lateral , group contains two toes, whereas the inner, Anatomical terms of location|medial , group contains three. On the rear feet this arrangement is reversed, the medial group containing two toes, and the lateral group three. These specialized feet allow chameleons to grip tightly onto narrow or rough branches. Furthermore, each toe is equipped with a sharp claw to afford a grip on surfaces such as bark when climbing. It is common to refer to the feet of chameleons as Dactyly|didactyl or Dactyly|zygodactyl , though neither term is fully satisfactory, both being used in describing totally different feet, such as the zygodactyl feet of parrots or didactyl feet of sloths or ostriches, none of which are significantly like chameleon feet. Although "zygodactyl" is reasonably descriptive of chameleon foot anatomy, their foot structure does not resemble that of parrots, to which the term was first applied. As for didactyly, chameleons visibly have five toes on each foot, not two.

Some chameleons have a crest of small spikes extending along the spine from the Anatomical terms of location|proximal part of the tail to the neck; both the extent and size of the spikes varies between species and individual. No generally convincing functional explanation for this feature has been proposed.

Senses

Chameleons have the most distinctive eyes of any reptile. The upper and lower eyelids are joined, with only a pinhole large enough for the pupil to see through. They can rotate and focus separately to observe two different objects simultaneously, this lets their eyes move independently from each other. This gives them a full 360-degree arc of vision around their body. When prey is located, both eyes can be focused in the same direction, giving sharp stereoscopic vision and depth perception . Chameleons have very good eyesight for reptiles, letting them see small insects from a long (5–10& nbsp;m) distance.
Like snake s, chameleons do not have an outer or a middle ear , so there is neither an ear opening nor an eardrum.Le Berre and Bartlett, 2009 However, chameleons are not deaf: they can detect sound frequencies in the range 200–600& nbsp;Hz.
Chameleons have very long tongue s (sometimes longer than their own body length) which they are capable of projectile use by living systems|rapidly extending out of the mouth. The tongue extends out faster than human eyes can follow, at around 26 body lengths per second. The tongue hits the prey in about 30 thousandths of a second. The tongue of the chameleon is a complex arrangement of bone, muscle and sinew. At the base of the tongue there is a bone and this is shot forward giving the tongue the initial momentum it needs to reach the prey quickly. At the tip of the elastic tongue there is a muscular, club-like structure covered in thick mucus that forms a suction cup. Ross Piper|Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals , Greenwood Press (publisher)|Greenwood Press . Once the tip sticks to a prey item, it is drawn quickly back into the mouth.

Chameleons can see in both visible and Ultraviolet light . Chameleons exposed to ultraviolet light show increased social behavior and activity levels, are more inclined to bask and feed and are also more likely to reproduce as it has a positive effect on the pineal gland .

Distribution and habitat

Chameleons are primarily found in the mainland of sub-Saharan Africa and on the island of Madagascar, although a few species are also found in northern Africa , southern Europe , the Middle East , southern India , Sri Lanka and several smaller islands in the List of islands in the Indian Ocean#Western Indian Ocean|western Indian Ocean . There are introduced, feral populations of Veiled Chameleon|veiled and Chamaeleo jacksonii|Jackson's chameleons in Hawaii and isolated pockets of feral Jackson's chameleons have been reported in California and Florida .

Chameleons inhabit all kinds of tropics|tropical and mountain rain forest s, savanna s and sometimes desert s and steppe s. The typical chameleons from the subfamily Chamaeleoninae are arboreal and usually found in trees or bushes, although a few (notably the Namaqua Chameleon ) are partially or largely Terrestrial animal|terrestrial . Most species from the subfamily Brookesiinae, which includes the genera Brookesia , Rieppeleon and Rhampholeon , live low in vegetation or on the ground among leaf litter . Many species of chameleon are threatened by extinction. Declining chameleon numbers are due to pollution and deforestation.

Reproduction

Chameleons are mostly oviparous , some being ovoviviparous .

The oviparous species lay eggs 3–6 weeks after copulation . The female will climb down to the ground and begin digging a hole, anywhere from 10–30& nbsp;cm (4–12& nbsp;in.) deep depending on the species. The female turns herself around at the bottom of the hole and deposits her eggs. Clutch sizes vary greatly with species. Small Brookesia species may only lay 2–4 eggs, while large Veiled Chameleon s ( Chamaeleo calyptratus ) have been known to lay clutches of 80–100 eggs. Clutch sizes can also vary greatly among the same species. Eggs generally hatch after 4–12 months, again depending on species. The eggs of Parson's Chameleon ( Calumma parsonii ), a species which is rare in captivity, are believed to take upwards of 24 months to hatch.
The ovoviviparous species, such as the Jackson's Chameleon ( Trioceros jacksonii ) have a 5–7 month gestation period. Each young chameleon is born within the sticky transparent membrane of its yolk sac. The mother presses each egg onto a branch, where it sticks. The membrane bursts and the newly born chameleon frees itself and climbs away to hunt for itself and hide from predators. The female can have up to 30 live young from one gestation.

Diet

Chameleons generally eat insect s, but larger species such as the Common Chameleon may also take other lizards and young bird s. The range of diets can be seen from the following examples:

The Veiled Chameleon, Chamaeleo calyptratus from Arabia , is insectivorous, but eats leaves when other sources of water are not available. It can be maintained on a diet of Cricket (insect)|Crickets . They can eat as many as 15-20 large crickets a day.

Jackson's Chameleon ( Trioceros jacksonii ) from Kenya and northern Tanzania eats a wide variety of small animals including ants, butterflies, caterpillars, snails, worms, lizards, geckos, amphibians and other chameleons, as well as plant material such as leaves, tender shoots, and berries. It can be maintained on a mixed diet including kale, dandelion leaves, lettuce, bananas, tomatoes, apples, crickets and waxworms.

The Common Chameleon of Europe , North Africa , and the Near East , Chamaeleo chamaeleon , mainly eats wasp s and mantis es; such arthropod s form over three quarters of its diet. Some experts advise that the Common Chameleon should not be fed exclusively on Crickets: these should make up no more than half the diet, with the rest a mixture of waxworm s, earthworm s, grasshopper s, fly|flies and plant materials such as green leaves, oats and fruit.

Temperature influence the amount of food eaten.

Change of color

The primary purpose of Animal coloration|color change in chameleons is social signaling, with camouflage secondary.
Color change signals a chameleon's physiological condition and intentions to other chameleons. Chameleons tend to show darker colors when angered, or attempting to scare or intimidate others, while males show lighter, multi-colored patterns when courting females.
Some species, such as Smith's Dwarf Chamaeleon|Smith's dwarf chameleon , adjust their colors for camouflage in accordance with the vision of the specific predator species (bird or snake) that they are being threatened by.

The desert dwelling Namaqua Chameleon also uses color change as an aid to thermoregulation, becoming black in the cooler morning to absorb heat more efficiently, then a lighter grey color to reflect light during the heat of the day. It may show both colors at the same time, neatly separated left from right by the spine.

Mechanism of color change

Chameleons have specialized cells, chromatophores , which contain pigment s in their cytoplasm , in three layers below their transparent outer skin:
# The cells in the upper layer, called xanthophore s and erythrophore s, contain yellow and red pigment s respectively.
# Below these is a second layer of cells called iridophore s or iridophores|guanophore s; these contain guanine , appearing blue or white.
# The deepest layer of cells, melanophores, contain the dark pigment melanin , controlling how much light is reflected.

Dispersion of the pigment granules in the chromatophores sets the intensity of each color. When the pigment is equally distributed in a chromatophore, the whole cell is intensively colored. When the pigment is located only in the centre of the cell, the cell appears mainly transparent. Chromatophores can rapidly relocate their particles of pigment, thereby influencing the animal's color. Chromatophores change because the cells get a message from the brain.

Video

Classification

Family Chamaeleonidae

Subfamily Brookesiinae

the Subfamily Chamaeleoninae

Parasites

Chameleons are parasite|parasitised by nematode worms including threadworms (Filaria) and roundworms. Threadworms can be transmitted by biting insects such as ticks and mosquitoes . Roundworms are transmitted through food contaminated with roundworm eggs; the larvae burrow through the wall of the intestine into the bloodstream.Le Berre and Bartlett, 2009. page 110

Chameleons are subject to several protozoan parasites such as Plasmodium which causes malaria , Trypanosoma which causes Animal trypanosomiasis|sleeping sickness , and Leishmania which causes leishmaniasis .

Chameleons are subject to parasitism by coccidia ,Le Berre and Bartlett, 2009. page 109 including species of the genera Choleoeimeria , Eimeria and Isospora .

Bibliography

Popular books

François Le Berre and Richard D. Bartlett. The Chameleon Handbook. Barron's Educational Series. 3rd Edition, 2009.

Linda J. Davison. Chameleons: Their Care and Breeding. Hancock House Publishers, 1997.

Philippe de Vosjoli. Essential Care of Chameleons. Advanced Vivarium Systems, 2004.

Copyright Citations

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