Species

Amphibian

Content Cover Image

California giant salamander, Copeland Creek, California. @ C.Michael Hogan

caption Treefrog Hyla cinerea. (Source: USGS Nonindigenous Aquatic Species)

The term amphibian comes from the Greek amphibios meaning "both lives". This is an apt description because most adult amphibians are better adapted to life on land than in water, while their larval phases are entirely aquatic.

For much of their lives, which may last a couple of months or several years depending on the species, larval amphibians bear little resemblance to their adult forms. Then something miraculous happens. In a matter of weeks or even days, the once fish-like larvae metamorphose into terrestrial, air-breathing quadrupeds!

There are three extant orders in the Class Amphibia: Anura (frogs and toads), Caudata (salamanders), and Apoda (caecilians). The order Anura has the most extant species, with 4000 members worldwide. Of Caudata, 390 salamander species exist worldwide. The third amphibian group, the caecilians, is smaller still with a total of only 162 species, all of which are restricted to the tropics.

Many species of amphibians are threatened, with principal threat classes consisting of anthropogenic alteration of surface water distribution due to agricultural land conversion and urbanization to serve needs of the exploding human population; other significant threats to species extinctions are excessive nitrate, herbicides and pesticides from agricultural practices.

Herpetology

caption Carolus Linnaeus, the father of modern taxonomy. (Source: (Source: Biodiversity Institute of Ontario)

The study of amphibians is often grouped together with that of reptiles under the heading "Herpetology", the base of which, 'Herpe-', is derived from the Greek word 'herpes' meaning "to creep". The mention of this term is enough to make many amphibian and reptile scientists cringe, since we recognize now that these two taxa are only distantly related. In fact, reptiles are more closely akin to mammals than to amphibians.

Despite this fact, for hundreds of years, scientists around the world failed to distinguish between these two vertebrate groups. Carolus Linnaeus, the father of modern biological classification, dismissed them as "foul and loathsome".

Today, the success of films such as Anaconda attests to our persistent fear of "cool blooded" creatures. However, a better understanding of them may persuade even the most timid observer that reptiles and amphibians are not only profoundly different but hardly "creepy" at all.

Amphibians and Reptiles

caption Megophrys nasuta , Malaysian Leaf Frog (Source: Olaf Leillinger at 2006-02-20 License: CC-BY-SA-2.5 and GNU FDL, via Wikimedia Commons)

Similarities

Both amphibians and reptiles are ectotherms, meaning that they derive heat from the environment, rather than producing it internally. To say that they are cold-blooded is imprecise since they, like endothermic vertebrates, need to keep warm in order to remain active.

Ectotherms are forced to slow down as their environment cools. Although this may put them at risk from predators, it can also be advantageous. Whereas an endotherm expends a tremendous amount of energy just to maintain a constant body temperature, a cold ectotherm can pass months at a time requiring little food or oxygen.

Differences

Aside from sharing the same mode of thermoregulation, amphibians and reptiles are very different organisms. While reptiles have internal fertilization and a waterproof scaly skin which allow them to live independent from water, amphibians are intimately associated with it. For the most part, amphibians are scaleless and their skin is highly permeable, requiring a source of moisture in order to prevent desiccation. In addition, most amphibians must mate in the water, where they deposit their soft, jelly-encased egg masses.

Additional Facts

  • caption The endangered Santa Cruz Long-toed Salamander Frogs, toads and salamanders drink with their skins rather than their mouths. Frogs and toads have a highly vascularized patch of skin on the belly and groin, called the "seat patch", which they use to drink the water that they're sitting in.
  • The way humans view frogs, toads and salamanders has changed throughout history. The ancient Chinese believed a giant frog held the world on its shoulders and several cultures associate frogs with fertility. In modern times frogs have been portrayed as enchanted princes, or as a happy character with a big heart such as "Kermit the Frog".
  • Toads are generally seen as villainous, probably due to their warty appearance and toxicity. However, Japanese legends bestowed toads with an all-knowing quality, and in the early twentieth century people began to recognize that toads have large appetites that are helpful in controlling insect populations. The Chinese don't refer to the "man on the moon", but know him as the "toad on the moon".
  • In medieval times, salamanders were thought to slither unscathed through fires, and their name means "fire animal". This legend arose from the fact that salamanders often hide in pieces of firewood and scurry away as it burns.
  • Amphibian toxins have been used by the Chinese to treat heart problems. Bufotenin, made from toad secretions, increases blood pressure by constricting blood vessels.
  • Some amphibians possess chemicals in their skin which have potential for use as painkillers.
  • Some indigenous Amazonian tribes use frog toxins to achieve a feeling of superhuman strength before they hunt.
  • The glandular secretions of the cane toad can be made into a hallucinogenic drug. Improper preparation of this drug, including "toad licking" has resulted in deaths.
  • One adult rough-skinned newt contains enough poison to kill 25,000 white mice, or a few humans.
  • Frogs and toads are the noisiest amphibians.
  • The Surinam toad (Pipa pipa), which occurs in South America, is tongueless and is so flat that it appears to have been run over.
  • The giant salamanders of China and Japan can reach up to 1.5 meters in length and weigh up to 12.7 kilograms.
  • Frogs first jumped in outer space in 1970 when NASA put two bullfrogs in orbit as a test of the effects of weightlessness on the inner ear.
  • Only Australia and Antarctica naturally lack true toads (Bufonidae), but even Australia is now overrun by the imported Cane toad, Bufo marinus. Originally from South America, cane toads were imported to Australia in 1935 in an attempt to rid the country of the greyback beetle, which was destroying the sugarcane crop.
  • Frogs have never been introduced to Iceland.
  • When some frogs eat something poisonous, they throw up their entire stomach! The stomach actually protrudes from the mouth, and they wipe it clean with their front legs.
  • Amphibians cannot tolerate the high salt concentration of seawater, so they are the only aquatic vertebrates that do not live in marine habitats.

References

Glossary

Citation

Ontario, B. (2014). Amphibian. Retrieved from http://www.eoearth.org/view/article/150028

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