Blanco Blind Salamander

Missing species have a hard time

The last time anyone saw a Blanco blind salamander in the wild was in 1951. At the time, a gravel operation working north of the Texan city of San Marcos excavated a spring in the dry riverbed of the Blanco River. Some water seeped out, and with it several white, almost translucent salamanders. What happened next was this: the gravel workers put four of the amphibians into a plastic bucket; two of the animals are said to have been eaten by a passing heron, and one was apparently lost. The fourth was identified as a new species. The adult female type specimen is still preserved today in a jar at the Biodiversity Center of the University of Texas.

More than 70 years have passed since the discovery of the Blanco blind salamander, and this single representative of the species remains the only one. The usual categories such as ‘vulnerable’ or ‘threatened with extinction’ do not really apply to it, because the amphibian is quite simply considered ‘missing’ (lost). We have neither proof of its existence nor proof of its extinction. No one knows whether the Blanco blind salamander is still alive at all. The category ‘missing’ includes species that scientists—depending on the definition—have not seen for at least ten or for more than 50 years.

For an organism, the status ‘missing’ is the worst imaginable, because it is often a species threatened with extinction for which no conservation measures are initiated, since no one knows whether it exists. In early 2022, the U.S. Fish & Wildlife Service (FWS) likewise decided that the Blanco blind salamander should not be classified as ‘threatened’ or ‘endangered’, because—as the reasoning went—it may already be extinct.

If the Blanco blind salamander has indeed become extinct, the reasons can only be speculated about. What is clear is that salamanders have semipermeable skin, which makes them vulnerable to contamination such as runoff from farms or sewage treatment plants. In any case, the IUCN cites deterioration or depletion of the aquifer in which the species occurred as possible reasons for its disappearance.

Blanco blind salamander – Fact sheet

alternative name	Robust blind salamander
scientific names	Eurycea robusta, Typhlomolge robusta, Typhlomolge robustus
original distribution range	Blanco River, Texas (USA)
date of extinction	unclear, no earlier than 1951
causes of extinction	unclear
IUCN status	Data deficient

Adapted to life in water and darkness

Cave-dwelling newts or salamanders belong to the family of lungless salamanders (Plethodontidae). They live mainly or exclusively in underground streams in caves and have special adaptations to this habitat. Some species, such as blind salamanders in Texas, have only rudimentary eyes or even no eyes at all; others lack any pigmentation, which is expressed in pale yellow or pinkish skin. The Blanco blind salamander—like other salamanders of the genus Eurycea—most likely spends its entire life in groundwater-filled caves below the surface; in other words, it is a stygobiont.

The blind and almost colorless Perrin’s cave diving beetle also lived in groundwater in southern France; it was last recorded in 1945. The blind scorpion Akrav israchanani , which occurred only in caves in Israel, is also probably extinct.

Furthermore, the lungs of all lungless salamanders are only rudimentary or absent altogether. They breathe through the skin, and partly also through the mouth cavity. The blind salamanders that occur in underground streams in Texas, such as the Blanco or Texas blind salamander, have external gills resembling feathery antlers, which they retain throughout their lives.

The IUCN gives the type locality for the Blanco blind salamander as an area below the Blanco River near the city of San Marcos in Hays County, Texas: an underground aquatic habitat in the Edwards Aquifer, one of the most productive artesian aquifers, but also one of the least accessible places in the world. The Edwards Aquifer is a complex underground cave system and porous rock formation extending across more than 10,000 square kilometers of south-central Texas. Crustaceans as well as various eyeless salamanders and blind fishes live there, one of which—Satan eurystomus, a catfish without pigmentation or externally visible eyes—is also considered ‘missing’. The Edwards Aquifer also serves as a vital drinking-water resource for two million Texans in the region.

What makes the search for the Blanco blind salamander so difficult

In 2006, researchers tried to track down the Blanco blind salamander at the Blanco River. Among other things, they excavated three surface fissures in the dry riverbed of the Blanco River, but these did not extend into underground cavities, so no salamanders could be found. They also examined groundwater springs north of the area where the Blanco blind salamander had once been discovered. Although the springs reached into underground habitats, they did not produce any Eurycea salamanders either.

From 2020 and 2021 onward, scientists focused on wells and springs in Hays County—so far without success. Texas blind salamanders, which are classified as vulnerable by the IUCN, by contrast, were regularly observed and collected at several sites in the city of San Marcos. In 2022, environmental journalist Benji Jones traveled to Texas to meet amphibian enthusiast Andy Gluesenkamp, who is leading an expedition to find the Blanco blind salamander. In his article for the U.S. magazine Vox, Jones describes what makes the search for the vanished blind salamander so difficult:

“Caving is also not the best way to try to find a Blanco blind salamander (…). Near San Marcos, there are not many of these natural entrances where the lost species could live (…). It is also possible that the salamander lives in pockets of water even deeper underground.”

Why scientists are desperate to find a salamander that’s been missing for 71 years, Benji Jones, Vox, August 1, 2022.

In some parts of the aquifer, the water is under such high pressure that it shoots to the surface and forms artesian springs. That makes it easier to search for animals that actually live in groundwater, because the springs bring the organisms to the surface, where scientists can catch them in nets. So far, scientists have had no success with this method in the search for the Blanco blind salamander—perhaps because the water sources were not at the right locations. This kind of search assumes that huge quantities of water would have to be examined to find a single individual: “Like using buckets to search for a hair tie in a warehouse the size of an Olympic swimming pool.”

Promising: environmental DNA for finding the Blanco blind salamander

A more promising method, which was also used in the search for the Loch Ness Monster and which may help locate the Blanco blind salamander, is, according to Gluesenkamp, an analysis of so-called environmental DNA, or eDNA. This is DNA traces from organisms in their environment, because all organisms constantly release DNA into their surroundings, for example through sneezing or dead skin and hair.

In the eDNA method, researchers take water, soil, or air samples and compare them with a database containing the DNA of known species. With this technique, parts of animal genomes can under certain circumstances be detected in the samples. Gluesenkamp wants to take samples from several dozen wells in Texas to search for the Blanco blind salamander. If the lost salamander lives anywhere near the place where a water sample was taken, part of its DNA must also be present in the water.

But there is a problem: scientists have no DNA from the Blanco blind salamander. Gluesenkamp instead wants to search for genes that belong to related species. If the analysis reveals DNA that is similar to that of other blind cave salamanders but does not match their DNA, this would indicate that the Blanco blind salamander exists. But that is far from enough to prove beyond doubt that the species has been rediscovered. Physical evidence is needed for that, so if DNA is found, Gluesenkamp would have to set traps to catch an individual. Only in this way can he say with certainty that he has found a Blanco blind salamander.

Is the Blanco blind salamander a Texas blind salamander?

Not everyone is convinced that the Blanco blind salamander is a distinct species at all. This includes the U.S. Fish & Wildlife Service, which for this reason, among others, felt prompted not to list the Blanco blind salamander as ‘endangered’ or ‘threatened’. The FWS expresses the suspicion that the salamander found in 1951 was a Texas blind salamander. The FWS report from March 2022 states:

“To be considered an endangered or threatened species under the law, it must be a taxonomically valid species. In assessing the status of the species, we found evidence that the Blanco blind salamander currently does not exist as a taxonomic entity. Several morphological characteristics of the Blanco blind salamander resemble or match those of the Texas blind salamander (…).”

Endangered and Threatened Wildlife and Plants; Three Species Not Warranted for Listing as Endangered or Threatened Species, Fish and Wildlife Service, Department of the Interior, Federal Register Volume 87, Number 49, March 14, 2022.

It is probably true that the Blanco blind salamander and the Texas blind salamander look similar, but they differ in size. The FWS has an explanation for this too: it could be due to the chemical fixation and preservation of the individual collected in 1951. This may mean that the original size of the living specimen is not reflected.

According to the IUCN, the Blanco and Texas blind salamanders are parapatric in the San Marcos Pool of the Balcones Aquifer near the city of San Marcos in Hays County in south-central Texas. This means that both derive from an ancestral species while sharing part of their distribution range. While the Blanco blind salamander is endemic to a small region beneath the Blanco River in the Edwards Aquifer, the Texas blind salamander occurs exclusively in cave waters of the Edwards Aquifer, especially in the San Marcos Pool.

Because of the hydrogeological connection, the FWS report says, movement between the site beneath the Blanco River and the places where the Texas blind salamander lives may be possible, so that a Texas blind salamander can also be encountered outside its actual distribution range. This would explain why they could be one and the same species.

There is also a counterargument: in their 1981 redescription of the Blanco blind salamander, herpetologist Floyd E. Potter and evolutionary biologist Samuel S. Sweet provide evidence that the geological formation in which the Blanco blind salamander occurs is hydrologically isolated from the one in which the Texas blind salamander occurs as a geographically neighboring species. This fact, in turn, would show that they must be two different species.

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