Eyeless and Other-worldly
The Texas blind salamander benefits from the scientific capabilities at the San Marcos Aquatic Resources Center

by Craig Springer

A watershed map of Texas shows the vast blue-line arteries that vein toward bigger waters and then, eventually, pour into the heart of the sea. Some watersheds are immense while others are comparatively small.

The Guadalupe River watershed, one of the smallest basins in Texas, belies the abundant, rich biological diversity found there—due in large part to the vast perforated-limestone Edwards Aquifer that lies beneath the surface. It follows that this phenomenon is a primary reason why the San Marcos Aquatic Resources Center (ARC) is situated where it is: the reliable water that exists near the San Marcos River, a tributary of the larger Guadalupe.

The San Marcos ARC mission is to conserve endangered, threatened and at-risk species. The facility is a refugium for an assortment of species, most of which are naturally found in the Guadalupe watershed and the Edwards Aquifer. The San Marcos ARC employees are immersed in culturing and researching the life-histories of these animals.

The Guadalupe and Edwards Aquifer harbor rare and unusual organisms that have some of the greatest conservation needs in the nation. The desire inherent in scientists to discover and answer more questions is no doubt sparked by rare organisms found around San Marcos. Animals such as the Texas blind salamander are beneficiary to the technical expertise available at this federal fisheries facility.
The Texas blind salamander looks other-worldly. Its body is bereft of color, and its head sports a pair of tiny black stubs, little stems where optic nerves could hold eyes.  But eyes never develop as they are never needed. This animal is almost never exposed to the light of day in its natural habitat; the dark watery labyrinth of the Edwards Aquifer.

The animal has been known to science since the 1890s when it was discovered in a well that fed the original San Marcos facility, then on the campus of Texas State University-San Marcos. But it remained understudied given that it lives its entire life in dark abysses deep underground.

The Texas blind salamander has been listed as endangered since 1967. It remains vulnerable, says San Marcos ARC director, Dr. Ken Ostrand. “They are impossible for scientists to sample underground, so we collect them in nets when they pop out in wells and springs, young ones, too small to fight currents,” said Ostrand. The young go into captivity at San Marcos ARC where they are held in refugia as a guard against potential harm that could come in the wild. Ostrand says their habitats, which he describes as a ‘limestone honey-combed sponge,’ are quick to recharge with surface precipitation, which could be accidentally laden with unwanted chemicals or spills. Preserving Texas blind salamanders in captivity is a security measure.

San Marcos ARC presently harbors 135 Texas blind salamanders collected in baited traps or in nets in caves and spring outflows and artesian wells. Each are maintained separately according to the nine collection site sources. They are also graded by size as cannibalism on eggs and smaller salamanders is a common occurrence in captivity and likely occurs in nature given the limited food found deep underground.

The eldest of the captive Texas blind salamanders approach 16 years of age. In that time, San Marcos employees have learned how to breed them in captivity. The learning curve has been steep, according to Ostrand.  “Common culture techniques don’t work; you can usually alter the amount of light exposure or adjust water temperature and induce reproduction in aquatic animals,” said Ostrand. “But that doesn’t work with an animal that evolved in water with a stable temperature and one that can’t see light.”

Recent research on the salamander has yielded other useful information. San Marcos ARC scientists collaborated with Texas State University faculty on a study of eye development in the Texas blind salamander and two other salamander species that live in the Guadalupe watershed: the San Marcos salamander and Barton Springs salamander, both of which are sighted animals that live near sunlight.  Both are held in refugium at the ARC as well.

The research revealed that the blind salamanders retained a vestigial optic nerve with no eyes while the other species had well-developed eyes with structures for focus and variable light adaptation. The findings will be published in a peer-reviewed scientific journal, and have already yielded a master’s thesis.

Other recent research with captive Texas blind salamanders has focused on bony and cartilage structures and body shape as compared to other related species in North America, as well as genetic relationships. Biologists commonly take tail tissues from salamanders for genetic analysis but now know that it’s important to do so sparingly with older animals. San Marcos ARC scientists learned that young salamanders regenerate tail tissue exceedingly quicker than older animals. Damaged tail tissue that takes a longer time to regrow leaves the animals more vulnerable to predation.

Aside from what has been learned about this animal that lives its life entirely in the dark, there’s another take-home message, notes the center director, “We don’t know enough. There’s much more research to perform so we can better understand this fascinating creature, both in where it lives, and how it survives.”

The Edwards Aquifer and east Texas are an emphasis area for the U.S. Fish and Wildlife Service’s Southwest Region, a geographic area where it will expend great effort to conserve a suite of organisms, including the Texas blind salamander. San Marcos ARC biologists care for a multitude of federally listed organisms on the station aside from the amphibians, such fountain darter, Comal Springs riffle beetle, Comal Springs dryopid beetle, Peck's Cave amphipod, Texas Wild-rice and Devils River minnow.

Craig Springer is with External Affairs in the USFWS Southwest Region and can be reached at Craig_Springer@fws.gov