Image of Shedd's Axolotls“Hey, man, you really wail on that axe.”

There will be no wailing on these axes, but, as you might have noticed, we do love a good stretch for our Jazzin’ Instrumentals focus animals.

Jazz can be hot or cool, smooth or groove, Chicago style or Kansas City, mainstream or avant-garde. The axolotls (ACK-suh-LAH-tuhls) are way avant-garde.

You’ll find four of these Mexican salamanders with the equally far-out Mexican blind cave tetras in the Rivers and Lakes gallery. While the cave tetras never develop eyes, the axolotls never develop into adults.

Most amphibians, including the majority of salamander and frog species, hatch from an egg and start life in a totally aquatic larval form that s quite fishlike, with gills, a legless body and a long tail. As they develop, they sprout legs, absorb the tail, lose the gills and become bona fide air breathers.

Axolotls only get as far as budding scrawny legs in the metamorphosis game. This lifelong larval state is called neoteny. An axolotl even looks babyish, with a broad, flat head, small, lidless eyes and a smiling mouth, framed by a fringe of feathery gills. The standout gills, combined with the permeable skin typical of amphibians, offer enough surface area to provide the stationary axolotl with adequate oxygen. Completing the tadpole look, a caudal fin runs most of the length of the body.

This is not to say, however, that axolotls don’t grow or mature sexually. In fact, they can grow to a foot and a half, although 6 to 9 inches is more typical, and they begin to reproduce at 18 months.

While axolotls remain in a state of arrested development, they have the ability to regenerate severed or damaged body parts, including whole limbs and even portions of the brain and spine, a talent that fascinates medical researchers.

They cannot, however, regenerate their environment. Axolotls were native to two adjoining high-altitude freshwater lakes in Mexico, Chalco and Xochimilco. These bottom-dwellers were the lakes’ top predator, detecting worms, insect larvae, crustaceans and small fishes by smell and sucking them down whole. But as nearby Mexico City expanded, Lake Chalco was drained, and only a remnant of Lake Xochimilco exists as a series of canals of polluted water. Add introduced predatory fishes and unabated collection for the pet trade to habitat destruction, and the last remaining wild axolotl population, which numbers fewer than 1,200 animals, is considered critically endangered and on the verge of extinction.

The axolotl is closely related to the terrestrial, fully metamorphosed tiger salamander. Scientists offer several possible explanations for the axolotl’s evolutionary U-turn. It might have been an adaptation to local environmental conditions, either in the water or on shore. Neoteny can be caused by insufficient levels of iodine, a naturally occurring and essential element for growth and development. It can also be a response to low water temperatures, which can suppress the production of growth hormones. Or perhaps dry land in the high altitudes in which axolotls evolved was so hostile that staying in the water, in the aquatic larval state, was the best survival tactic.

Whatever the initial inducer, neoteny is now programmed into the axolotl’s genes. Rarely, an individual will metamorphose spontaneously, but such animals are not long-lived. Whatever fountain of youth axolotls originally crawled into, neoteny has served them well: In their normal larval stage, they can live between 10 and 15 years.

Our amphibian Peter Pans will take us out, perhaps playing “I Won't Grow Up,” on the final night of the 2012 season of Jazzin’ at the Shedd, which has been sponsored by Bank of America.

In marine and freshwater environments alike, the aquatic life resembles a perfectly tuned jazz band. Each plant and animal species has a unique note to play; together they form an extraordinarily beautiful, complex arrangement. At Shedd, our conservation and research programs work to keep the music playing without missing a note.

Karen Furnweger, web editor