Texas Blind Salamander
© 2019 Tom Devitt (1 of 13)
Eurycea rathbuni (Stejneger, 1896)
1. Historical versus Current Distribution. Texas Blind salamanders (Eurycea rathbuni) were first described by Stejneger (1896; as Typhlomolge rathbuni) from a 58 m-deep artesian well drilled in 1895 in the city of San Marcos, Hays County, Texas, on what is now the campus of Southwest Texas State University. These salamanders are known from several caves, wells, and pipes that intersect the San Marcos Pool of the Edwards Aquifer in San Marcos and are unlikely to range beyond this region (for more detailed discussions of this species with respect to hydrogeology of the region, see also Uhlenhuth, 1919; Russell, 1976; Longley, 1978; Potter and Sweet, 1981; Chippindale et al., 2000). Status of the genus Typhlomolge as distinct from Eurycea has been controversial (e.g., Mitchell and Reddell, 1965; Wake, 1966; Mitchell and Smith, 1972; Potter and Sweet, 1981), but it is now clear that "T." rathbuni and its presumed sister species "T." robusta are phylogenetically nested within the central Texas Eurycea and should be considered species of Eurycea (Chippindale, 1995, 2000; Chippindale et al., 2000). Petranka (1998) recently followed this taxonomic approach. Eurycea rathbuni plus E. robusta, and a newly described species from Austin (Hillis et al., 2001) appear to represent the sister group to other central Texas Eurycea from south of the Colorado River.
2. Historical versus Current Abundance. Densities of cave-dwelling populations of the central Texas Eurycea are difficult to assess. For several years after drilling of the artesian well at San Marcos (in the late 1800s), over 100 individuals emerged annually; this number soon dropped to a few per year (Uhlenhuth, 1921). Individuals of this species still appear common in outflows of Diversion Spring, a pipe that carries outflows from the Edwards Aquifer at San Marcos (Aquarena) Springs; most individuals that emerge probably are eaten by fishes, but salamanders can be captured if a net is placed over the pipe's outflow. However, numbers collected vary widely from year to year; currently, most individuals recovered are juveniles (J. Fries, personal communication). The National Fish Hatchery at San Marcos, Texas, currently maintains approximately 180 individuals, almost all obtained as juveniles, captured over a 4-yr period by netting two wells that provide outflow from the Edwards Aquifer (J. Fries, personal communication). Individuals of this species can reliably be observed at a tiny cave opening into the Edwards Aquifer in San Marcos (Russell, 1976; personal observations, early 1990s). When the cave floods, Texas Blind salamanders are active on the surface in broad daylight (personal observations).
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Unknown.
ii. Breeding habitat. Unknown in nature. However, this species has laid eggs on numerous occasions in captivity at the Dallas Aquarium at Fair Park, the Cincinnati Zoo, the Aquarena Center (San Marcos), and the San Marcos National Fish Hatchery and Technology Center (L. Ables, Dallas Aquarium at Fair Park, personal communication).
i. Egg deposition sites. In nature, unknown.
ii. Clutch size. Unknown.
C. Larvae/Metamorphosis. Texas Blind salamanders are paedomorphic, and natural metamorphosis is unknown. Attempts to artificially induce transformation through use of thyroid hormone resulted in only partial metamorphosis (Dundee, 1957). Captive-hatched individuals at the Dallas Aquarium at Fair Park grew from approximately 10 mm to 80–90 mm TL in about 14–16 mo (L. Ables, personal communication). Grobman (1957) investigated the thyroid gland of this species, and Sever (1985) provided information of sexual dimorphism of the cloacal glands of this species.
D. Juvenile Habitat. Probably similar to adult habitat.
E. Adult Habitat. Completely aquatic. Found in caverns of the San Marcos Pool of the Edwards Aquifer, where they have been observed climbing rock surfaces or swimming in open water. Water temperature of the spring outflows of this region of the Edwards Aquifer is relatively constant at approximately 21–21.5 ˚C throughout the year (Berkhouse and Fries, 1995).
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Unknown.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). Probably active throughout the year.
K. Interspecific Associations/Exclusions. No other salamanders are known from the subterranean habitat of this species, although San Marcos salamanders (E. nana) are abundant in springs directly above the caves occupied by this species.
L. Age/Size at Reproductive Maturity. Petranka (1998) listed the size of adults as 90–135 mm in total length. Brandon (1971b) found that males mature at about 40 mm SVL, and females at about 40–50 mm SVL. Captive-raised females at the Dallas Aquarium at Fair Park displayed visible eggs (and deposited infertile eggs) at approximately 35 mm SVL (L. Ables, personal communication). Courtship and reproduction was documented by Belcher (1988), and captive reproduction has occurred at the Dallas Aquarium at Fair park, the Cincinnati Zoo, the Aquarena Center (San Marcos), and the San Marcos National Fish Hatchery and Technology Center (L. Ables, personal communication). Reproduction in the wild probably occurs throughout the year (Longley, 1978).
N. Feeding Behavior. Prey probably consists primarily of subterranean invertebrates; Longley (1978) reported amphipods, snails, and cave shrimp (Palaemonetes antrorum) as food items. One individual was seen skimming the water surface in a cave, perhaps seeking insects on the water's surface (personal observations). An individual outside a flooded cave was seen feeding on an earthworm (personal observation), and captive specimens will eat meat (Norman, 1900). This species will readily enter traps baited with potato peels; this may be due to the bait's attraction for aquatic invertebrates (Russell, 1976; personal observations).
O. Predators. Unknown.
4. Conservation. Texas blind salamanders are known from several caves, wells, and pipes that intersect the San Marcos Pool of the Edwards Aquifer in San Marcos and are unlikely to range beyond this region. Populations have been lost, and they are listed as Endangered by both the State of Texas (www.tpwd.state.tx.us) and the Federal Government (http://ecos.fws.gov).
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 May 2019.
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