AMPHIBIANS—: FROGS, TOADS, SALAMANDERS AND THE FROG-KILLING FUNGUS

AMPHIBIANS

Amphibians such as frogs, toads and salamanders are cold-blood, egg-laying vertebrates. There are three orders: 1) Anura (frogs and toads); 2) Caudta (salamanders and newts); and 3) Gymnophiona (caecilians, legless wormlike creatures that live in leaf litter or streams). As of 2006 there were 5,700 know species of amphibians. Of these about a third are endangered.

Most amphibians need to keep their skin moist. They are in danger of dying if their skin dries out too much. All amphibians exude chemicals from their skin. After handling one you should wash your hands and refrain from putting your fingers in your mouth, eyes or ears.

Amphibians need to live near water and lay their eggs in water. Most amphibians lay soft shell-less eggs in water and abandon them. As is true with fish, the eggs are mostly fertilized outside the female’s body. The offspring are born with feathery gills used for breathing in water. Many amphibians burrow into the soil. Those with keel-shaped heads tend to scoop dirt side to side while those with round heads tend to ram straight ahead into the soil.

Amphibians are a food for larger animals and help keep insect populations and algae in check. The Americas are particularly rich in amphibian species but this is at least partly because detailed survey have not been done in places like West Africa, India, Sri Lanka and New Guinea. According to the IUCN Red List by the World Conservation Union list one in three amphibians species is threatened.

Websites and Resources: Amphibian Research Center frogs.org.au ; Frogworld frogworld.net/category/unusual-frogs ; Frogland allaboutfrogs.org ; Frog Photos calphotos.berkeley.edu/browse_imgs/amphibian ; Amphibian and Frog Photos mongabay.com/topics/amphibians ; National Geographic National Geographic ; Amphibian Web amphibiaweb.org ; Wikipedia article on Amphibians Wikipedia ; Save the Frogs savethefrogs.com ; Amphibian Specialist amphibians.org ; Amphibian Ark amphibianark.org ; Froglife froglife.org

Websites and Resources on Animals: ARKive arkive.org Animal Info animalinfo.org ; Animal Picture Archives (do a Search for the Animal Species You Want) animalpicturesarchive ; BBC Animals Finder bbc.co.uk/nature/animals ; Animal Diversity Web animaldiversity.ummz.umich.edu ; International Field Guides media.library.uiuc.edu ; animals.com animals.com/tags/animals-z ; Encyclopedia of Life eol.org ; World Wildlife Fund (WWF) worldwildlife.org ; National Geographic National Geographic ; Animal Planet animal.discovery.com ; Wikipedia article on Animals Wikipedia ; Animals.com animals.com ; Endangered Animals iucnredlist.org ; Endangered Species Resource List ucblibraries.colorado.edu ; Biodiversity Heritage Library biodiversitylibrary.org

History of Amphibians

First emerging about 350 million years ago, amphibians were the first backboned creatures to walk on land and they ruled the Earth for about 100 million years until they were eclipsed by reptiles. Amphibians are regarded as more primitive than reptiles because reptiles such as iguanas show physiological changes associated with pleasure’a rise in heart rate and body temperature’but amphibians don't.

The origin of amphibians is not completely understood as there are huge gaps in the fossil record. Frogs and salamanders are thought to have evolved from ancient amphibians known as temnospondyls while caecilians evolved from lepospondyls, another group of ancient amphibians. In 2009, a fossil of a 290-million-year-old “frogmander” was found that had traits of both frogs and salamanders. The discover of the creature, called Gerobatrachus, was announced by scientists from the University of Calgary in Nature in May 2008.

Frogs and Toads

Frogs are generally found in the water while toads are generally found on land. Frogs are usually spend more time in water but are comfortable on land. They have clammy skin without scales and lay masses of eggs in a jelly-like mass. Both their skin and eggs are highly permeable. [Source: Virginia Morell, National Geographic, May 2001]

Frogs first emerged 190 million years ago. Today there are more than 3,500 species of frog and toads. Scientist discover about 50 new species a year. The live all over the wold, including the driest deserts, Arctic tundra, seawater mangrove swamps and up to 18,000 feet on the Tibetan plateau.

Frogs generally have sleek, slippery and smooth skin while toads are covered with rough warts. Frogs zip around with long jumps, while toads prefer to amble along with a slow walk, although when pressed they can execute short hops.

Frog Characteristics

Frogs feed on mosquitos, aquatic insects, worms, crawfish, small fish and occasionally the chicks of small waterbirds. Frogs have long sticky tongues. They can open their mouth, snag an insect with their tongue and pull it into their mouths fast than the blink of an eye. The circles behind the eyes are the drumheads of the ears.

Frogs are powerful swimmers and good jumpers. They are generally solitary, and usually most active at night, particularly on rainy nights. Some frogs hibernate by burrowing in the mud. The North American wood frog can survive off long as seven months in sub-freezing temperature, with the help of natural antifreeze in it body.

Tree frogs can climb tree trunks and building walls with their sticky toe pads. Some tree frogs can change their color to match their background. The can accomplish this with several layers of chromatophores, special color cells that can be opened or closed to adjust to skin color. Tree frogs lay their eggs in water like all amphibians.

Many frogs secrete compounds through their skin that have powerful antibiotic properties. Some frogs roll themselves into a ball and lie still to conserve water.

Frog Songs

The croaks, trills, peeps, grunts made by frogs are purely vocal and are produced the same way humans make sound do by pushing air back and forth through their vocal chords. Some frogs have vocal sacs on the other side of their throat that amplifies the sound.

Frogs are great singers. Only male frogs sing. They do so to attract females and inform males of their presence. Sometimes they call hundreds of time a night. Herpetologist Stan Rand told National Geographic, "It's the most energetically expensive thing a male frog ever does."

Before singing a frog sucks in a full load of air and then closes its nose and mouth. The air is pushed through into the vocal sac, which looks like an inflated balloon. Some species have one sac under the chin. Other species have two sacs, one on each side of the cheeks. Each species of frog has its own distinct song.

Predators sometimes use the songs to locate frogs. Frogs are fed on by a number predators, including snakes, herons, hawks, mammals and large fish. They escape by jumping, diving and swimming away. Many kinds of snake like to feed on frog eggs. When threatened by a snake the eggs one species Panamanian frog hatch prematurely.

Studies have shown that some species of frog response not only the calls and silences of their species for warnings of predators but also monitor the calls of other frog and animal species for clues on the presence of predators like bats, snakes and birds.

Breeding Frogs

Frogs gather together in the breeding season. Depending on the kind of frog, the females lay between 2,000 to 8,000 eggs. Mating usually takes place in ponds, pools or streams on rainy nights, with the male fertilizing the eggs while they float on the surface or they emerge from the female. Amplexus is the name of the embrace employed by the male on the back of the female while she is producing eggs. A pair of frogs can remain in this embrace for hours.

Among many species, the males protect the eggs. Some carry the froglets on their backs or even swallow the eggs and keep them in their vocal sacs until the froglets emerge from their mouth.

The development of a tadpole into a frog is called metamorphosis. Embryos develop into tadpoles in the jelly of the egg. After a few days when the tadpoles are strong enough they break out of the jelly and begins feeding on larvae. At this stage the tadpoles are not very developed. Over the following days they develops tails and external gills. Later they develop internal gills like a fish.

Depending on the species, the tadpole stage can last several weeks to a few years. During this time the tadpole is essentially a plant-eating fish. Then a remarkable metamorphosis takes place: it grows a set of lungs and then begins breathing oxygen from the air. The lungs grow larger and the gills become smaller and eventually disappear. Around this time legs appear and grow; the tail shrinks and disappears; and the mouth develops a hinged jaw. When the transformation is complete, an insect- and animal-eating frog is complete.

Toads

Toads are slow-moving creatures. They are generally not fast enough to escape predators. Instead they defend themselves with small organs called parotid glands that release poison and are found behind the ridges of their eyes or are arranged along the backs of the toad are two parallel rows. When stimulated these glands release a milky liquid which contain powerful poisons called bufotoxins. The poisons are powerful enough to paralyze a small dog, cat, weasel or fox. They can cause death if squirted into the mouth of a small animal. If you handle a toad wash your hands afterwards.

Toads feed on worms, spiders, pill bugs, centipedes, ground beetles, earthworms, and other crawling creatures, insects and small animals. Relaying an camouflage to hide their presence, they like to ambush their prey, lying still waiting for it pass and then zap its with a sudden movement from their sticky tongue — sort of like a chameleon — to lasso their prey. Potential predators that feed on toads include snakes, weasels, dogs and cats.

Toad mating and egg-laying take place in shallow ponds. The process usually takes place in the spring, beginning with long wrestling matches that can last for days between males trying to win the right to mate with the females. Sometimes the males try to mate with the females while simultaneously wrestling with several male rivals.

The fighting stops when the female finally lays her eggs which are fertilized outside her body by males who squirt their sperms over the eggs. As the eggs emerge, females secrete a jelly-like substance that surrounds and protects the eggs. The spawn is produced in the form of long, thin gelatinous ropes, which contain several thousand eggs. A few weeks later tadpoles appear and stay in the water for several months and eventually crawl out as baby toads.

Salamanders

Newts and salamanders spend most of their daily lives on land. they are primarily nocturnal, In the had they like to hide in moist leaf litter or rotting logs. They mate and breed in water.

Red-back salamanders are monogamous creatures that can be mean to their partners if they start engaging in throat notes with other salamanders, by withdrawing affection.

One of the most bizarre salamanders is the axoloyl, a 15-centimeter-long species found in Mexico that has beady eyes, a goofy smile and a head crowned with frilly gills that look like a strange alien headdress. Scientists like the creatures — also known as “water monsters” — because they reproduce easily im the lab, are able to regrow limbs, jaws, skin, organs and parts of its brain and spinal chord and have clear skin so yu can see what is going on.

Some salamanders are able to grow back limbs that they have lost. Other animals can do this but what makes salamanders special is that they regrow many different body parts over and over throughout their life. After a salamander loses a body part, blood vessels contract quickly and limit bleeding. Skin cells then work fast to cover the wound and form what is called “blastena” — a collection of stemlike cells that will eventually become a new body part.

In Mexico City, scientists are genetically modifying axoloyls that are able to regrow limbs, jaws, skin, organs and parts of its brain and spinal chord in hopes being able to do the same with humans someday.

Decline of Amphibians

A total of 120 amphibian species disappeared between 1980 and 2006. One biologist called it “one of the largest extinction spasms of vertebrate in history.” Another said was the largest potential extinction since the dinosaurs.

According to the official Red List by the World Conservation Union one in three amphibian species is threatened. About half are in decline. Nearly a quarter are endangered or extinct.

In some places the populations of frogs, salamanders and other amphibians have crashed and in some cases become extinct. In other places amphibians have developed gross deformities such as extra legs or misplaced eyes. Possible causes of these problems include interspecies competition, climate change, ultraviolet radiation from a thinning ozone layer, pollution, overharvesting, disease and habitat destruction.

Pollution is blamed for some of the decline. Frogs have highly permeable skin and eggs that easily admit toxins. In some places introduced bullfrogs, trout and other fish species have driven out local species by gobbling up the local species and their eggs and outcompeting them for food. Studies have shown of the deformities seemed to be caused by tiny parasitic flat worms not chemical, pollution or global warming.

The situation is so dire that scientists launched a massive “Noah’s ark’ to capture frogs, toads and salamanders and put them in safe places. During the first stage of the project amphibians were collected and placed in houses and hotels rooms until new buildings to house could be built. The most intensive collecting is taking place in Mexico, Ecuador, Colombia and Panama.

Frog-Killing Fungus

Populations of frogs and amphibians have been devastated by the chytrid fungus, a disease of unknown origin that affects only some species and so far is beyond control. The microscopic fungus attaches to victims and thickens their skin, making it difficult for them to absorb water they need to survive. The disease is particularly widespread in Central and South America and Australia.

The spread of chytrid fungus is thought have occurred as a result of human activity. It probably introduced by African clawed frogs which were widely exported around the globe in the 1930s for medical research and pregnancy tests (frogs injected with the urine of pregnant women began laying eggs). It may have also been carried bullfrogs raised in South America for the United States frogs legs market.

In Panama 48 amphibian species have come down with chytridiomycosis with their numbers plunging as much as 90 percent. In 2007 the chytridiomycosis fungus was found in pet frogs in Tokyo, the first cases of the disease in Asia.

Amphibians and Climate Change

In January 2006, Alan Ponds of the Monteverde Cloud Forest Preserve and Tropical Science Center in Costa Rica authored a study published in Nature that showed a link between frog deaths from chytridiomycosis fungus and global warming. The study focused on the disappearance of 70 species of harlequin frog in Central and South America. “Disease is the bullet killing frogs, but climate change is pulling the trigger,” Pounds said.

They seem to grow well under cool day time conditions and hot nighttime ones. In rainforests global warming might actually cause a cooling trend in the day as more clouds might be generated by a warming affect. More clouds could cause higher temperatures at night as the cloud keep warm air from escaping into space. The chytridiomycosis fungus grows better under these conditions.

Image Sources:

Text Sources: Mostly National Geographic articles. Also “Life on Earth” by David Attenborough (Princeton University Press), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011


This site contains copyrighted material the use of which has not always been authorized by the copyright owner. Such material is made available in an effort to advance understanding of country or topic discussed in the article. This constitutes 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. If you are the copyright owner and would like this content removed from factsanddetails.com, please contact me.