Range and Habitat of Salamanders
Salamanders are found throughout much of the world at altitudes up to 4,000 m (13,000 ft). In the western hemisphere their range spreads across the United States and Canada and extends south through Central America to the northern portion of South America. Salamanders also live in Europe, the Mediterranean area, Africa, and Asia, including the islands of Japan and Taiwan. Salamanders are not found in Australia, New Guinea, New Zealand, Madagascar, or Antarctica.
Physical Characteristics of Salamanders
An adult salamander has a slender, elongated body with a long tail, and in most cases, two pairs of legs roughly equal in size. Most salamanders are drab in color, but some, such as fire salamanders, have brilliant yellow, orange, or red markings. The majority of salamanders measure 10 to 15 cm (4 to 6 in) in length, but the smallest known salamander reaches just 2.7 cm (1.1 in), and the Japanese giant salamander grows to 1.5 m (5 ft).
Those salamanders that spend all or part of their lives on land tend to be slight, with small heads, slender bodies, and a sprawling gait that comes from moving the two legs that are diagonally opposite one another at the same time. Aquatic salamanders, such as the amphiuma, are usually larger, and they often have reduced limbs. Some aquatic salamanders, such as the greater siren, have no hind legs at all. The front limbs of most species end in four fingers, and the rear limbs typically end in five toes. Like other amphibians, salamanders do not have claws. Some salamanders can force their ribs through their skin to act as protective barbs, providing a defense against predators.
Salamanders are the only amphibians that have long tails as adults. They use these tails, which are often as long as their bodies, for balance in walking and propulsion in swimming. Many salamanders can shed their tails if a predator threatens them. Once shed, the tail reflexively flails about on the ground and distracts the would-be predator while the salamander slips away and later regenerates a new tail.
Salamanders are also able to regrow limbs that are lost or injured. Scientists are studying the genetic and hormonal processes that allow salamanders to regenerate body parts such as jaws, spinal cords, and brain parts in addition to tails and limbs. Because some of the same genes are present in humans, research into salamanders could lead to medical treatments that would allow humans to regrow or repair damaged organs and limbs.
Like all amphibians, salamanders have delicate, permeable skin through which water and gases, such as oxygen and carbon dioxide, can enter and leave the body. Most adult salamanders have saclike lungs for breathing air and use their permeable skin only as a source of supplemental oxygen. Some species never develop lungs and instead obtain oxygen through gills or through their skin and the mucous membranes of their mouths and throats. Salamanders also have glands in the skin that secrete a thick layer of mucus. On land, this mucus prevents the skin from drying out, and in water, it helps maintain the correct balance of salt and water in salamanders’ body fluids. Other glands in salamander skin secrete toxic poisons. Salamanders equipped with poison-producing skin glands often display bright colors and conspicuous markings, possibly to warn predators that they are poisonous to the touch. Male salamanders commonly have skin glands that produce scent-emitting chemicals called pheromones that play a role in courtship and mating.
Most salamanders have well-developed eyes. They also have nasal sensory organs capable of detecting chemical changes in the environment. These nasal organs serve an important function in feeding, courtship, and locating breeding sites. Their sense of hearing is poor, and salamanders rarely make noise, although some species are known to make faint squeaks or yelps when excited or disturbed.
Diet of Salamanders
Most salamanders are carnivorous—that is, they eat other animals rather than plants. Adult salamanders that live in water prey on the larvae of frogs, known as tadpoles, and various invertebrates, including snails and worms. Some also eat small fish. These salamanders locate prey by smell and ingest it by opening their mouths in the water and sucking in their prey.
Terrestrial salamanders rely on vision to find food. Most are solitary, sit-and-wait opportunists that eat soft-bodied invertebrates, including insects, slugs, and worms. When one of these prey animals unwittingly comes within reach, the salamander rolls its fleshy, sticky tongue out of its mouth to snatch it up. Some tropical salamanders have projectile tongues that they can extrude from their mouths for distances equal to 40 to 80 percent of their total body length to snap up unsuspecting prey.
Many salamanders are nocturnal—that is, they do most of their hunting in the cool, dark hours of night and remain inactive during the day. Those that are active during daylight retreat to the cool depths of bushes and other ground cover during the hottest period of the day. Some groups are active only during certain seasons. When conditions are too cold or too dry for them to muster the energy necessary to find food, these salamanders enter a resting state similar to hibernation. The siren spends much of its time burrowed in the muddy bottom of seasonal ponds and ditches that dry up in the heat of the summer. When the mud and sand starts to dry, the mucous coating on its skin hardens to form a protective cocoon, which enables the siren to survive out of water for many weeks.
Reproduction in Salamanders
For many types of salamanders, mating begins with complex courtship behavior. Some terrestrial male salamanders create scent trails to attract females. Among lungless salamanders of the western hemisphere, males initiate courtship by using their chins to rub the heads of females. As they rub, they secrete chemicals that stimulate the female. Among European newts, such as the crested newt, courtship takes place in water, and during the mating season, males acquire bright colors and intricate tail fins to attract mates.
Among most salamanders, fertilization occurs internally, meaning the egg and sperm unite inside the female’s body. During mating, salamanders use the cloaca, a chamber that opens into the animal’s digestive and urinary tracts as well as their reproductive tracts. Mating pairs of salamanders may position themselves with the muscular openings of their cloacae touching so that the male can transfer sperm directly to the female. Among many terrestrial and aquatic salamanders, males release one or more sperm-filled capsules called spermatophores onto the ground, then attempt to induce a female to pick up the spermatophores with the opening of her cloaca.
Among some very ancient types of salamanders, including hellbenders, fertilization is external. Females of these species deposit eggs in sacs or strings in the water. Male hellbenders release their sperm over the eggs to fertilize them, then guard the eggs until they hatch.
Among salamanders that have internal fertilization, females may either deposit their eggs on land or in water or, as in the fire salamander, retain the eggs within their bodies, eventually giving birth to live young. Among tiger salamanders, females lay eggs in clutches of up to 500 eggs in streams or ponds. Females of other species lay eggs singly or in small clutches at terrestrial sites, such as in rotting logs. Females that lay small clutches typically protect their eggs from hungry predators until hatching occurs.
Life Cycle of Salamanders
The life cycle of salamanders varies greatly among species. All salamanders have a larval stage in which they have external, feathery gills for breathing in water. Among salamanders that lay their eggs on land, the larval stage occurs inside the egg. In salamanders that give birth to live young, the larval stage takes place within the body of the mother. Only some salamander larvae actually live in a body of water such as a pond or stream.
Many salamander larvae undergo a transformation called metamorphosis, in which their bodies change in ways that make them better suited to life on land than life in the water. During metamorphosis, the larvae of most species lose their gills and acquire a pair of saclike lungs. The heart transforms from the two-chambered heart needed to support gills to a three-chambered heart capable of supporting lungs. The larvae also grow limbs, eyelids, and well-developed tongues.
Many larvae undergo metamorphosis in two or three months. Some, including hellbenders, take up to five years to mature. Many salamanders, including mud puppies, undergo partial metamorphosis and as adults retain some larval characteristics, such as gills. Other salamanders, such as the Mexican axolotl, never undergo metamorphosis unless they are exposed to certain chemicals in a laboratory. These amphibians retain many characteristics of larvae for their entire lives, except that they develop reproductive organs. Still others, such as the tiger salamander, metamorphose only if the ponds that they live in become uninhabitable and they must make the transition to land to survive.
Hellbenders are capable of surviving for 25 years in their natural settings, and some fire salamanders have survived as long as 50 years in captivity. The life span of most salamanders in the wild is unknown.
Declining Salamander Populations
alamanders are extremely sensitive to changes in their ecosystems, and the health of local salamander populations often mirrors the health of the habitat as a whole. Evidence suggests that habitat destruction, particularly forest clear-cutting, is severely depleting salamander populations. Especially vulnerable are those salamanders that live in the temperate forests of North America and in tropical forests of Asia and South and Central America, where deforestation is occurring at an alarming rate.
Mysteriously, some salamander populations are declining even in apparently pristine areas that have not been destroyed for human development. Non-native predators and competitive species whose range has been extended by humans may threaten salamander populations. They also appear to suffer at higher than normal rates from diseases caused by viruses, bacteria, or fungi. The chytrid fungus that causes the disease chytridiomycosis affects the skin of amphibians and is a particular threat to salamanders and frogs.
Although no one knows for sure, many researchers believe that the impacts of competitive species and disease are exacerbated by a variety of environmental problems. These problems include pollution and increased levels of ultraviolet light penetrating the atmosphere as a result of the thinning ozone layer. Rapid climate change associated with global warming can also affect local climates where salamanders are adapted to live.
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species designates many salamanders as vulnerable to extinction or endangered. Species that are listed as critically endangered include the giant Chinese salamander and the axolotl. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) also recognizes all giant salamander species and the axolotl as endangered and prohibits trade for commercial purposes. The U.S. Fish and Wildlife Service lists a number of salamanders found in the United States as threatened or endangered species, including the California tiger salamander and the Texas blind salamander.
Scientific classification: Salamanders make up the order Caudata in the class Amphibia. Newts and fire salamanders belong to the family Salamandridae; the crested newt is classified as Triturus cristatus and the fire salamander as Salamandra salamandra. The hellbender, the giant Chinese salamander, and the giant Japanese salamander belong to the family Cryptobranchidae and are classified as Cryptobranchus alleganiensis, Andrias davidianus, and Andrias japonicus, respectively. The smallest known salamander is a member of the lungless salamander family, Plethodontidae, and is classified as Thorius arboreus. The Texas blind salamander is also in the Plethodontidae family and is classified as Eurycea rathbuni. Sirens make up the family Sirenidae; the greater siren is classified as Siren lacertina. Mud puppies belong to the family Protidae; the widest-ranging mud puppy is classified as Necturus maculosus. The tiger salamander and the axolotl belong to the family Ambystomatidae and are classified as Ambystoma tigrinum and Ambystoma mexicanum, respectively.
Source by : http://en.wikipedia.org/wiki/Salamander
http://encarta.msn.com/encyclopedia_761558552/salamander.html
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