The Austin Blind Salamander is known only from Barton Springs. Unlike the Barton Springs Salamander, Austin Blind Salamanders are not typically seen near the surface. Austin Blind Salamanders occupy the habitat below the surface of the springs, where their unique adaptations likely give them a selective advantage in a world of total darkness and limited food. They have been found in all four of the springs collectively known as Barton Springs: Parthenia in Barton Springs Pool, Old Mill (Sunken Garden), Eliza and Upper Barton. Unfortunately, because their habitat is not readily accessible by humans, and they are only occasionally observed in the springs, very little is known about the natural history of this species.
Old Mill Spring (Sunken Garden) in Zilker Park is the site where the Austin Blind Salamander (Eurycea waterlooensis) was first collected.
Interestingly, another large spring in Texas is also home to a pair of salamander species: San Marcos Springs in San Marcos (Hays Co.) has surface-dwelling San Marcos Salamanders (Eurycea nana) as well as the subterranean Texas Blind Salamanders (Eurycea rathbuni).
All three Eurycea salamanders that inhabit Austin springs are members of the family Plethodontidae, which is the largest family of salamanders. They are within the sub-family Spelerpinae, which includes four genera: Eurycea, Gyrinophilus, Pseudotriton, and Stereochilus. A total of thirteen species are now described from this group of (mostly) perennibranchiate salamanders that inhabit central Texas.
Very little was known about any of Austin’s endemic brook salamanders prior to the 1990s, even though they consisted of three very different species. Prior to discovery and formal description of each species, the majority of brook salamanders (genus Eurycea) found in spring-fed surface streams throughout the Edwards Plateau of central Texas (including the Jollyville Plateau) were considered Eurycea neotenes, the Texas Salamander. In the mid-1990’s, biologists undertook studies to understand the ecology (the relationships between the salamander and its environment) and evolutionary history (e.g., the genetic relationships between the salamander and other species) of this group of salamanders. Through those studies, biologists discovered that the Texas Salamander was, in fact, comprised of several genetically distinct species. The true range of the Texas Salamander is actually restricted to the springs and caves of Bexar, Comal, and Kendall Counties. Two of the newly discovered species were Austin’s own E. tonkawae, the Jollyville Plateau Salamander2, and E. sosorum, the Barton Springs Salamander1.
The primary reason so many different species across a relatively broad geographic range were considered conspecific (the same species) is that all of the Edwards Plateau species are very similar in appearance. Before the invention of methods to examine DNA and protein molecules, differences in physical appearance, or “morphology,” were the basis for distinguishing one species from another. At that time there was no evidence to classify the Edwards brook salamanders as separate species. Once scientists learned how to test molecules and use the results to identify and group species based on their genetic relationships (the science of molecular systematics), the unique genetic characteristics of each species of salamander became apparent, and each could be classified.
Of course there were some exceptions to this prior “lumping” of different species under one name. Most notably are the subterranean species, Austin Blind Salamander, Blanco Blind Salamander, and the Texas Blind Salamander, who exhibit very obvious and extreme differences in the morphology of their bodies and heads. For one, they are “blind,” or to be more specific, they lack an image forming eye. They also tend to have larger, shovel-shaped heads. These features are believed to confer an advantage for living in complete darkness, although scientists still debate the origin of troglomorphic characters as “regressive evolution” or resulting from natural selection. Before the discovery of the Austin Blind Salamander in Barton Springs, the members of this group were considered to be in a different genus altogether (Typhlomolge) because of their extreme morphology. But once again the molecular data2,3 allowed biologists to learn that these species are genetically similar enough to the other Edwards Plateau species to be included in the genus Eurycea.
A cladogram showing the evolutionary relationships of the central Texas Eurycea salamanders. Species that occur in Austin are highlighted in grey. Branch lengths do not reflect genetic distance or substitution rate. Note that none of the species in Austin are each other’s closest relatives; thus illustrating the complex and interesting evolutionary history of this group. From Chippindale et al. 2000 and Hillis et al. 2001.
Range map of all the central Texas Eurycea salamanders.
Most of what we know about the life history of Austin Eurycea is based on observations made of the salamanders while in captivity. While many of these observations are of the Barton Springs Salamander, some characteristics (such as courtship) are thought to be common to the whole group. Courtship behavior involves a series of steps called a “tail-straddling walk,” which is characteristic of the family (Plethodontidae) of salamanders to which central Texas Eurycea belong. In the “walk,” the female straddles the male’s tail and rubs her chin on the base of his tail as he walks slowly forward; he stops at times and undulates his tail, possibly dispersing pheromones or showing her the location of his spermatophore. He eventually deposits a spermatophore that she will pick up in her cloaca. The eggs will be fertilized as they pass through the oviduct as they are being laid. After courtship, the female may wait months or a year or more before she lays her eggs. It is not known whether multiple males sire a single clutch of eggs.
The female (white eggs are noticeable in her abdomen) follows the male, he undulates his tail, possibly showing her where he has deposited his spermatophore.
All three species are thought to lay their eggs in the aquifer below the surface (especially so for the Austin Blind, who rarely visits the surface). This is because only a few eggs have ever been found in the wild; those eggs were thought to have accidentally washed up on the surface of the spring. Egg-laying events have only been observed in captivity.
On average, a female lays 15 eggs in a clutch. The eggs are laid singly and this process can take 12 hours or more. The ova are white and are surrounded by several layers of a clear capsule that is permeable for gas exchange. The capsule protects the embryo and is sticky, which presumably allows the female to lay the eggs on rocks in flow.
This is a time lapse video of embryo development for the Barton Spring Salamander. Notice the development of the eyes, gills, front limbs, and the heart beating in the throat area. This individual developed the back limbs after hatching.
The eggs hatch in 3-4 weeks. Hatchlings are ~½” total length (snout to tip of tail), often without fully formed limbs. Juvenile salamanders become sexually mature at about 11 months (50mm total length) and grow to about 3 inches as adults. Salamanders can continue to reproduce to an age of at least eight years.
The salamanders are one-half inch in length when they hatch and grow to about 3 inches in total length as adults. They have a muscular tail used for swimming. They do not spend much time swimming in the water column, however, and instead walk along the substrate*. They have 4 toes on their front feet and 5 toes on their back feet. The color variation for the Barton Springs Salamander includes shades of pink, purple, brown, orange, red as well as white spots called iridophores. The Austin Blind Salamander is generally lavender or purple with white iridophores.
This is a cleared and stained specimen of E. sosorum. The “clearing” process makes proteins transparent while the “staining” stains all cartilage blue and bone red. This is a very useful technique to allow researchers to study the bone structure of an amphibian without destroying the connective tissue.
The Barton Springs and Jollyville Plateau salamanders have eyes with image-forming lenses to help them see predators and prey. In contrast, the Austin blind salamander only has eyespots that may help it detect light. It cannot see and does not need eyes in the darkness of the aquifer.
Notice the color variation between the individual Barton Springs Salamanders shown in the video of the animals in the wild (see section on Austin Blind).
Central Texas Eurycea are aquatic their entire lives. This video shows how aquatic salamanders respire. This close-up of an Austin Blind Salamander shows red blood cells rapidly moving through capillaries in the salamander’s external gills. In this process, the red blood cells pick up oxygen in the water and release carbon dioxide as they move through the gills, just like our lungs when we breathe air.
These photos were taken of the same individual Jollyville Plateau Salamander, but several months apart spanning a dry period. Notice the drastic difference in gill size. Salamander gills will change in size in response to their environment over time. Large bushy gills help in an oxygen-poor environment, such as when the springs go dry and they must retreat underground to follow the water table.
*substrate-the rocks and sediment on the bottom of the stream
Most of what we know about the ecology of Austin’s aquatic salamanders is from studies conducted by the City of Austin on the more easily accessible surface populations. Their diet, like most salamanders, is entirely carnivorous. Based on field observations, fecal content analysis, and new radio-isotope data, they eat a variety of prey that is likely based on both what is available and what fits in their mouth. This includes a variety of snails (Gastropoda), seed shrimp (Ostracoda), copepods (Copepoda), amphipods, insects (such as midge, mayfly, and damselfly larvae, aquatic beetles, etc.), flatworms (Planaria), segmented worms (Annelida), and others.
Amphipods in Eliza Spring.
Barton Springs Salamander eating Amphipods
Predatory Fish
Relationships between the salamanders and their predators are not well understood. Some evidence suggests freshwater sunfish and basses opportunistically feed on salamanders. In the past, many salamander habitats were too shallow to harbor these fish species. Now these fishes have more available permanent and stable habitat in salamander streams because of direct and indirect stream channel modification by humans (e.g. dams creating Barton Springs Pool). Predatory fish presence may hinder dispersal where unnatural intermittent pools intercept the stream pathways that were once more shallow riffles or runs. Recent evidence clearly shows that chemical cues from predatory fish can negatively affect salamander activity.
Crayfish are common in both shallow and deep waters and can be found in nearly every salamander habitat. Crayfish are generalist predators, eating a variety of things from fish and tadpoles to plants and detritus, and have been observed feeding on juvenile Barton Springs Salamanders.
So, it is not unlikely that they are also a common Jollyville Plateau Salamander predator. Interestingly, the burrows created by crayfish may be beneficial in some ways to Jollyville Plateau Salamanders. One theory is that crayfish burrows may act as a path for salamanders to retreat through dense sediment and gravel to reach subsurface waters during dry periods.
Other large invertebrates have been observed feeding on salamanders. Giant water bugs (Lethocerus uhleri) are large ambush predators (up to 65mm) and have been seen at several monitoring sites preying on salamanders, ranid tadpoles, and mosquito fish (Gambusia affinis).
Damselfly larvae of the genus Archilestes are long and slender ambush predators that prey on very small juveniles if given the opportunity.
Cannibalism has also been documented in this species. Adults have been observed regurgitating the remains of juvenile salamanders when captured. This in part helps to explain why juveniles are often found in areas where adults are not, such as in very shallow water on the edge of the stream.
Unlike the surface populations, cave-dwelling Jollyville Plateau Salamanders are the top predators of that ecosystem. The downside, however, is that prey availability is much lower. Because all troglobitic organisms live in total darkness, there are no primary producers, so they must rely on nutrient input from the surface. The salamanders likely feed on available troglobitic and troglophilic (can live inside and outside caves) crustaceans and insects and potentially accidental prey washed into the caves during rain events.
Because the Barton Springs Salamander and the Austin Blind Salamander are federally endangered species, the City of Austin must have a permit from the U.S. Fish and Wildlife Service to continue the operation of Barton Springs as a recreation area. The permit is issued under the Endangered Species Act Section 10(a)(1)(B) and is referred to as an incidental take permit. The City’s first incidental take permit was issued in 1998 and would have expired in October 2013.
The federal permit is based on conservation measures described in a Habitat Conservation Plan. The Barton Springs Habitat Conservation Plan details the actions the City will conduct that adversely affect the Barton Springs Salamander and the Austin Blind Salamander and their habitats, and how the impact of those actions will be reduced or compensated to protect both species. The plan can only cover actions by the City in and around Barton Springs that may affect the Barton Springs Salamander or the Austin Blind Salamander and does not involve any actions associated with the federally threatened Jollyville Plateau Salamander in northwest Austin or actions outside of the City's jurisdiction in the contributing zone of the Edwards Aquifer.
City salamander biologists revised and expanded the Habitat Conservation Plan for Barton Springs in July 2013 after a 2-year process involving citizen input and extensive coordination with the U.S. Fish and Wildlife Service. The current incidental take permit from the U.S Fish and Wildlife Service was issued in September 2013 and will expire in 2033.
You can download a copy of the City’s incidental take permit and associated habitat conservation plan here.