On Waterdogs, Mudpuppies, and the Occasional
Hellbender
by Alex Hawes
Frogs and toads arent the only creatures leading double lives on land and underwater. While roughly 75 percent of the worlds 4,500-plus amphibian species are indeed frogs, the class Amphibia does boast a wide assortment of otheroften bizarrelife forms. Just take a gander at the Tennessee cave salamander (Gyrinophilus palleucus), a pale creature with a pinkish collar of gills, adapted for life in the cavernous pools of the Cumberland Plateau. Or the mysterious axolotl (Ambystoma mexicanum), an Aztec-named amphibian that lurks beneath the surface of Mexicos Lake Xochimilcoand there only. Or the worm-like caecilians, a little-understood group of burrowing amphibians from the tropics, growing up to five feet long.
Apart from frogs and toads (order Anura), the remaining amphibians fall into either the order Caudata, which includes newts and salamanders, or the order Gymnophiona, the caecilians. All amphibians are ectothermic (cold-blooded), and require moisture for their sensitive skins. Anurans generally hatch as tadpoles in the water, then metamorphose into terrestrial-minded frogs and toads. However, many salamanders (including those species in the family Proteidae, labeled "mudpuppies" in the North and "waterdogs" in the South) adopt neotenymaintaining their original, aquatic form throughout life. Most caecilians, on the other hand, skip the juvenile stage and hatch fully metamorphosed.
"Eye of newt and toe of frog, wool of bat and tongue of dog," begins the infamous recipe for the witches brew in Macbeth. Newt eyes, however, are not terribly potent, visually-speaking. Some newt and salamander species see quite poorly; others, like the rare Blanco blind salamander (Typhlomolge robusta), see not at all. Only the lungless salamanders (Plethodontidae) have the well developed depth perception characteristic of mammals and birds. Instead, many salamanders, newts, and caecilians navigate via smell and touch. As opposed to their crooning frog cousins, salamanders and caecilians also remain silent usually, capable only of the occasional click, snap, or "yelp," according to researchers.
In ancient myth, salamanders possessed skin so cold that it protected them from fireperhaps a result of people witnessing salamanders escaping from burning logs. In truth, their skins may be slimy, but are hardly impervious. Amphibians do maintain a moist layer of film to protect against bacteria, to reduce friction when swimming, and even to slip away, literally, from predators. The skin of certain North American newts contains toxins of similar chemical composition to the poisons of pufferfish. These newts, however, are dangerous only through ingestion, not through contactunless you have an open wound. Their toxins take effect only through the bloodstream. Such species often wave their tails about when threatened, luring predators to a spot where most of their toxins are concentrated. Fire salamanders (Salamandra salamandra) take a more proactive approach, squirting toxic secretions more than six feet to discourage foes.
The woods and wetlands of North America offer some of the best opportunities for discovering frogs amphibian cousins. Of the nearly 400 species of salamander and newt, more species inhabit the New World than all other regions combined, including all 230 or so species of lungless salamander. The United States and Canada alone support more than 150 species of newt and salamander, ten of which are currently listed as threatened or endangered. (No caecilians, however, live in North America.)
Salamander numbers can be staggering if you know where to look. In one Texas pond, the combined weight, or biomass, of the lesser sirens (Siren intermedia)an aquatic salamander two feet in lengthwas found to exceed the total biomass of the ponds seven species of fish. Researchers surveying Shenandoah National Park one wet night encountered a density of up to ten redback salamanders (Plethodon cinereus) per square meter. But if squishing through swamps and turning over logs isnt your idea of fun, the National Zoos Reptile Discovery Center hosts three-toed amphiumas (Amphiuma tridactylum) and Eastern hellbenders (Cryptobranchus alleganiensis alleganiensis), while at Amazonia youll find aquatic caecilians (Typhlonectes natans) in Dr. Brasils Field Station.
-Alex Hawes
ZooGoer 29(2) 2000. Copyright 2000 Friends of the National Zoo. All rights reserved.
