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Geckos

Geckos

Distribution and habitat

Physiology and reproduction

Defensive behavior

Resources

Geckos are small night-lizards found in the tropics and subtropics, and number more than 1,100 species in the family Gekkonidae, divided into four subfamilies (the Diplodactylinae, the Gekkoninae, the Sphaerodactylinae, and the Eublepharinae). Only the Eublepharinae have eyelids, while members of the other three subfamilies have transparent scales protecting their eyes.

Geckos are small lizards, ranging in length from less than 2 in (5 cm), to seldom more than 1 ft (30 cm). They are primarily insectivorous and nocturnal, and are unique in that they are the only lizards with a true voice. Depending on the species, geckos utter anything from a soft, high-pitched squeak to a loud bark. The name gecko arose as an attempt by humans to mimic the sound made by a common North African species (Gekko gekko ). Geckos have a soft, scaly, often transparent skin which readily tears away, allowing the little creature to escape the jaws or beak of a predator. Special toe pads enable geckos to walk upside down across rocks, on ceilings, and up the walls of city skyscrapers. Geckos are thought to have originated in Southeast Asia and the western Pacific, but are now found in large numbers in the warmer parts of every continent, and even on isolated islands around the world. Geckos make popular house pets, since they are harmless, relatively unafraid of humans, and provide effective and natural control of insect pests, such as the cockroach. Geckos may live as long as 15 years in their natural environment, but seldom that long in captivity.

Distribution and habitat

Geckos began their migration from the Pacific Rim thousands of years ago, some stowing away on the canoes of unsuspecting sea voyagers; others

beginning colonization from eggs deposited under the bark of logs subsequently swept out to sea and washed up on a distant shore. As humans moved from forest and land dwelling, building cities in which artificial lights illuminate the night skies attracting billions of insects, geckos also migrated from their original habitats to these new urban feasting grounds. Today, flicking on the light in the middle of the night in apartments, homes, and even tall office buildings in many parts of the world, one may interrupt the nocturnal feeding foray of one of these little creatures.

Only a small number of gecko species occur in North America. The tiny, two-inch-long, leaf-toed gecko (Phyllodactylus tuberculoses ) thrives in southwestern Californian among the rocks of semiarid lower mountain regions and canyon lands. The banded gecko inhabits southern Californias coastal plains, rocky deserts, juniper-covered hillsides, and sand dunes. Several species of West Indian geckos are now established in Florida, and many different species thrive on the Hawaiian Islands.

Physiology and reproduction

The texture and color of a geckos skin provides excellent camouflage. Four strong legs and five specially-equipped toes on each foot provide for excellent climbing abilities, while two round eyes with vertical pupils allow sharp, nocturnal vision. Diurnal (daytime) geckos, such as the wall gecko (Tarentola maur-itanica ), of North Africa, Spain, and Croatia, have rounded pupils.

Geckos do not have a forked tongue. They use their tongues to help capture prey and somelike the Australian naked-toed gecko and the Asian tokay geckouse their tongues to clear their eye scales of dust and debris. The head is relatively large in comparison to the tubular-shaped body, and the long, sheddable tail comprises up to one half of the total body length, snapping off in sections if it is grabbed by a predator. The discarded tail wriggles around on the ground, distracting the attackers attention and providing precious seconds for the animal to flee. A new tail grows back within a few months. The tail also stores fat, providing nutrients in times of food scarcity. Being cold-blooded creatures, geckos draw their body heat from their environment by basking in direct sunlight or on warm surfaces.

When mating, the male gecko grasps the skin at the back of the females neck in his jaws and wraps his tail around that of the female, bringing their cloacas the reproductive openingtogether. Some species of gecko reproduce asexually, when the female produces fertile eggs without mating with a male. All geckos, except some species found in New Zealand, lay eggs. Some species lay one egg in each clutch while others lay two. Eggs are deposited under rocks, tree bark, and even behind window shutters. Only a few species lay two clutches per year and incubation may take several months. Eggs of the banded gecko and of many other species have a leathery, parchment-like texture, while those of such species as the leaf-toed gecko have a hard, calcareous (containing calcium) shell, the durable nature of which has aided in the wide-spread distribution of many species, particularly the species that reproduce asexually, where just one viable egg can begin a whole new colony.

Defensive behavior

The Australian spiny-tailed gecko (Diplodactylus williamsi ) displays the most unique defense of all lizards. When this gray, inconspicuous gecko suddenly swings opens its jaws, it displays a vivid, dark purple mouth outlined in bright blue. It may also emit a high-pitched squeak and, if attacked, shoots a thick, gooey liquid from spiny knobs on its tail, covering its enemy with a sticky weblike substance.

Although geckos in general show aggressive displays such as arching the back, stiffening the limbs to increase their height, and wagging their tails, they are relatively nonaggressive, fighting among themselves only when defending a homesite or feeding territory from a determined invader. Although small geckos will attack a foe many times their size if threatened. The Australian barking gecko (Underwoodisaurus milii ) barks and lunges even at humans. Very few

KEY TERMS

Asexual Able to reproduce without male fertilization.

Calcareous Containing calcium carbonate.

Cloaca The cavity into which the intestinal, genital, and urinary tracts open in vertebrates such as fish, reptiles, birds, and some primitive mammals.

Diurnal Refers to animals that are mainly active in the daylight hours.

Thermoregulate Regulate and control body temperature.

species of gecko are strong enough to break the human skin, and none are poisonous.

See also Reptiles.

Resources

BOOKS

Bustard, Robert. Australian Lizards. Sydney: Collins, 1970.

Conant, Roger, et al.A Field Guide to Reptiles & Amphibians of Eastern & Central North America. Boston: Houghton Mifflin, 1998.

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

Zweifel, R.G., H.G. Cogger, and D. Kirshner, eds. Encyclopedia of Reptiles and Amphibians. 2nd ed. Academic Press, 1998.

PERIODICALS

Autumn, Keller. How Gecko Toes Stick. American Scientist (March-April 2006): 124132.

Petren, Kenneth, and Ted J. Case. Gecko Power Play in the Pacific. Natural History (September 1994): 5260.

Petren, Kenneth, Douglas T. Bolger, and Ted J. Case. Mechanisms in the Competitive Success of an Invading Sexual Gecko over an Asexual Native. Science 259 (January 15, 1993): 354357.

Marie L. Thompson

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