Amphibians
Tennessee Cave Salamander
Gyrinophilus palleucus · also called pale salamander
Deep inside the limestone caves of the southern Cumberland Plateau, in cold streams that never see daylight, lives a salamander that is, in a sense, permanently young. The Tennessee cave salamander hatches, grows, and breeds without ever losing its gills or leaving the water. Almost no one has seen one in the wild.
Overview
Gyrinophilus palleucus is a paedomorphic salamander — it keeps its larval body for life. Adults are pale pink to whitish, up to about 22 cm long, with small, skin-covered eyes, a broad flattened head with a squared snout, and three pairs of large red external gills. It lives only in the underground streams of limestone caves in central Tennessee, northern Alabama, and north-western Georgia.
A larva for life
Most salamanders transform from a gilled aquatic larva into an air-breathing adult. This one does not. It reaches breeding age still carrying gills, a tail fin, and soft larval skin, and it stays in the water permanently. Its own genus includes the spring salamander, a surface-stream animal that metamorphoses normally, so the Tennessee cave salamander looks very much like a spring salamander larva that became locked into cave life.
Hidden, and vulnerable
The species is known from only a few hundred caves, many with small populations. Its greatest threat comes from above ground: cave streams are fed by surface water sinking through sinkholes, so runoff of fertiliser, silt, sewage, and quarry dust from the land overhead can poison a population that no one ever sees.
Status
The Tennessee cave salamander is listed as Vulnerable and is thought to be declining, mainly through groundwater pollution, sedimentation, and disturbance of its caves. Protecting the land that feeds each cave stream is the key to conserving it.
Tennessee Cave Salamander: common questions
Why does the Tennessee cave salamander keep its gills for life?
It is paedomorphic, a condition in which an animal becomes sexually mature while still in its juvenile body. Most salamanders hatch as aquatic, gilled larvae and later transform into air-breathing adults that can leave the water. The Tennessee cave salamander skips that change. It grows larger and reaches breeding condition but keeps the external gills, tail fin, and soft larval skin of a larva, and it stays in the water permanently. In cave streams, where conditions are stable and food on land is absent, there is little advantage in transforming and a real cost to losing the gills, so natural selection has favoured staying larval.
Is the Tennessee cave salamander blind?
Not fully, but its eyes are reduced. They are small, sometimes partly grown over with skin, and almost certainly of limited use in the permanent darkness of a cave. The animal relies instead on touch, on water-borne vibrations picked up by sensory pits and the lateral line system along its body, and on smell and taste to find prey and avoid danger. This is a partway stage compared with the Texas blind salamander and the grotto salamander, which have gone further and lost functional eyes almost entirely, and it fits the idea that the species has not been isolated underground for as long.
How is it different from a mudpuppy or a spring salamander?
The mudpuppy is a much larger, permanently aquatic salamander of open rivers and lakes across a wide area of eastern North America, with a different body plan and no dependence on caves. The spring salamander is the Tennessee cave salamander's own close relative, in the same genus, but it lives in cool surface streams and springs, has full-sized eyes, and metamorphoses into a stout terrestrial adult. The Tennessee cave salamander looks like a spring salamander larva that never left the cave, pale and permanently gilled, and the two are thought to share a recent common ancestor.
Why is a cave animal threatened by things on the surface?
Because a cave stream is not sealed off. The water in it fell as rain on the land above, ran across fields and roads, and sank into the ground through sinkholes and fractures in the limestone, carrying with it whatever it picked up. Fertiliser and pesticide runoff, silt from construction and logging, leaking septic systems, quarry dust, and fuel spills all reach the underground stream within hours or days. A cave salamander population can be wiped out by a pollution event at a sinkhole kilometres away, and because the animals are hidden, the loss often goes unnoticed. Protecting the recharge area on the surface is the main way to conserve the species.