Incognito: Nature’s Hidden Marksman

Incognito: Nature’s Hidden Marksman

A small lizard slowly inches along a branch. The vocals of birds in the background fill the forest, and the sounds of scuttling terrestrial mammals below can also be heard. The forest is alive as ever, but this one creature is focused on one thing and one thing alone. Its turret-like eyes are locked onto a small grasshopper about a foot away. The insect is feeding on the leaves of a separate branch and cannot see the camouflaged stalker. Most lizards would give up on this one, since they would not be able to silently sneak up on this prey item without loudly jumping over to branch. However, this lizard is very different. It judges the distance between it and the prey item. Then, it orients itself to a better position. Everything is ready. The lizard opens its mouth, and via complex musculature, its tongue shoots out of the mouth. In less than one-hundredth of a second, the prey is hit and the tip of the tongue grasps the insect. With the prey now seized, the tongue retracts and the grasshopper is pulled back to the mouth of the lizard and meets its doom. The reptile’s jaws clamp shut and the strike is a success. This hidden predator has performed this technique many times before. It’s just another day’s work for the chameleon.

The chameleons are a sizable group of lizards consisting of 135 species. They are distributed from throughout most of Africa, but their populations also extend eastward to India and north to Spain. They are mostly known for their abilities to extend their tongues in order to catch prey and also to change color (making for some fantastic displays). The more we study these unique reptiles, however, the more we see just how complicated they can be. Take their tongue strikes, for example. Iguanids (the lineage of lizards which chameleons belong to) have well designed tongues for grasping and bringing prey to their mouths. However, chameleons take this ability to the next level. [1]

Chameleons are among the most unique animals in the world. curiousanimals.net

All lizards’ tongues are supported by the hyoid (lingual) bone, with the tip of the tongue supported by a single rod of the hyoid bone. This is the lingual process. An intricate system of musculature moves the tongue, or certain parts of it, for the purposes of swallowing, grasping prey, and so on. When a chameleon is ready to strike and opens its mouth, the hyoid apparatus is pulled forward and the tongue protrudes as a result. Lying near the tip of the tongue is an accelerator muscle. This muscle serves to extend the tongue out of the mouth. When the chameleon activates it, this muscle contracts and exerts a force around the lingual process of the hyoid. Much like how squeezing something slippery will cause it to shoot out of your hand, the tongue will then shoot out of the lizard’s mouth. The tongue brings the retractor muscle with it. The retractor usually lies coiled around the basal part of the lingual process when at rest. When stretched, it is usually equal to or greater than the length of the chameleon’s body (minus the tail). It determines the distance that the tongue may be extended, though the chameleon may lessen the distance by actively firing the muscle. The prey item is grasped by a glandular pad through a process combining wet adhesion and muscular activity. With the prey caught the retractor fires and pulls the tongue back to the chameleon’s mouth. The hyoid is retracted, closing the mouth. All of this, incredibly enough, occurs in less than a second.[2]

 

A chameleon extending its tongue to catch its prey. Animalplanet.com ©

To support this excellent system, chameleons possess the two turret-like eyes which are unique to them. The eyes can be moved independently of one another, providing the chameleon with the depth perception it needs for aiming its tongue and checking the distance between it and its target. Their feet have opposable sets of partially fused toes. This makes climbing trees easy for them. Their special limb girdles allow them to hold their slender limbs close to their bodies in order to walk on perches with small diameters. The tail is prehensile and is used like a fifth limb. Interestingly, the skin of the tail is never shed.[3]

Color changing is another trait shared by a variety of lizards, but most can’t compete with the camouflage skills of chameleons. They easily blend in with their surroundings, and their leaf-shaped bodies help them to resemble leaves when in trees or on the ground (not all chameleons are arboreal). Changes in color are not always for camouflage, though; chameleons change color according to their emotions as well. An angered male will develop bright color patterns as a warning to other males entering his territory, or when disturbed by someone or something that is getting too close for comfort. Temperature is another factor associated with color changing. At night, the temperature is lower and the chameleons react to the cool temperature by becoming white. They may resemble white leaves on the ends of twigs. It is said that sleeping near the ends of twigs protects chameleons from predators, as the larger animals would be too heavy to travel on top of slender branches.[4] A strategy used by small chameleons involves dropping to the ground and staying still. Resembling one of the many leaves in the leaf-litter, the chameleon is virtually invisible.

But how exactly do chameleons change color? Chameleons possess special cells called chromatophores. These cells have red or yellow pigment on their top layers and blue or white pigments on their lower layers. The pigment cells change due to signals from the chameleon’s brain. They then enlarge or shrink. When the cell pigments mix, the change occurs and the chameleon’s skin color changes. Melanin is a chemical that also helps chameleons to alter their color. The fibers of this chemical can spread throughout the pigment cells. When this occurs, the chameleon’s skin darkens.[5]

 

Chameleons will show off strong coloration for a variety of reasons. Animalplanet.com ©

Males of most, if not all, species are territorial. They have no patience with other males entering their turf and, as mentioned before, will immediately develop a threat display pattern of colors. If the warning doesn’t make the intruder back off, then the territorial chameleon will proceed to hiss at the opponent. If that can’t do the trick, then it will all come down to fighting. The chameleons will bite each other aggressively until one or the other cannot take the abuse anymore. This usually takes place during mating season. Some chameleons are specially equipped for these events. Male Jackson’s chameleons (Chamaeleo jacksonii), for example, possess horns on their heads which are used for identification between sexes and possibly combat between the males.[6]

Jackson’s chameleons possess an interesting set of horns which could possibly be useful during competition between males for females. factzoo.com

Some species of chameleons give birth to live young. Most, however, lay eggs. The number of eggs per clutch varies between species as well as body sizes. A large species like the Meller’s chameleon (Chamaeleo melleri) can lay up to 70 eggs. However, many chameleons have smaller clutches of around 30 or 40 eggs. The eggs are usually hidden in moist protected areas.[7]

All of these features have made chameleons very successful in expanding their populations. Like all reptiles, they are masters of survival. They can be found in humid forests, Mediterranean climates, and deserts. They have earned their reputation as survivors, as well as the interest of many biologists. Among the iguanian lineage, chameleons stand out for these features which have kept them one step ahead. They truly are nature’s hidden marksmen.

[1] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.

[2] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.

[3] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.

[4] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.

[5] Cooper, Sharon. “Chameleons.” National Geographic.com. Available from http://magma.nationalgeographic.com/ngexplorer/0210/articles/mainarticle.html. Internet; accessed 19 October 2010.

[6] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.

[7] Coupe, Sheena. Encyclopedia of Reptiles and Amphibians. San Diego, CA: Academic Press, 1998.

Featured photo file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.