IUCN threat status:

Vulnerable (VU)

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Texas blind salamander (Eurycea rathbuni)

The Texas blind salamander is a rare, aquatic, cave-dwelling salamander native to the San Marcos Pool of the Edwards Aquifer, San Marcos, Hays County, Texas [6] at an elevation of 600-750 m. Specimens have been collected at 7 localities in the Purgatory Creek system and along the San Marcos Fault. In some sites it is known only from individuals washed out of artesian wells. Adults and immature larvae are well-adapted to live in underground streams in caves and many probably inhabit deep recesses; some occur in wells (11). Pools where this species has been collected have minimal current and nearly constant temperature of 21-22º [8]. The first specimens were collected in 1895 from a newly constructed well that drew water from 58 m below the surface.

The animal has a very broad, flat head and snout and is virtually pigmentless. The four limbs are very thin and elongate; the forelimbs have 4 digits, while the hind limbs have five. The tail is laterally compressed and finned, tapering at its end. The non-functional eyes are vestigial and lie beneath the skin; juveniles have proportionally larger eyes. The animal is neotenic and retains its bright red external gills throughout life; these absorb oxygen from the water. It has 12 costal grooves. Adults are 8.3-14 cm long [9,10]. The animal has a tail stradddling walk, climbs rock surfaces and swims in open water. It does not make significant seasonal or local extended movements and shows no distinct annual or daily activity patterns. Its diet varies by what flows into its cave, including blind shrimp, snails, amphipods and copepods [1]. Bat guano is an important source of nutrients in the subterranean ecosystem inhabited by this species.

This species is neotenic/paedomorphic and does not metamorphose fully. Dunn (2) noted that a laboratory specimen laid a few eggs on March 15 and a specimen collected in early autumn had the spermatheca packed with spermatozoa. Very small juveniles have been found throughout the year, suggesting a seasonal breeding pattern [1] . Bechler [3] saw the species breed in a laboratory. Courtship begins when the female approaches the male and rubs her chin on his back. She may also rub her cloaca on nearby rocks while rocking to and fro. If the male does not respond, the female may fan her tail at him or nip him along the sides or use her hind limbs to kick gravel to scratch him. She eventually straddles the tail of the male and rubs her snout above the tail base. The male responds by arching his pelvic region and fanning his tail between her legs. The female then rubs her snout more rapidly over the base of the tail. The male may lead the female forward and repeat the same cycle while slowly vibrating the anterior third of the tail. He eventually bends the body laterally and moves the tail laterally at a right angle to the body, while the female continues rubbing the base of the tail. The male leads the female forward, bends his body into an S-shape and deposits a spermatophore on a rock or substrate and leads the female forward with the tail extended laterally until she picks up the spermatophore cap with her cloacal lips (3). The spermatophore consists of a crescent-shaped white sperm cap over a clear, gelatinous base that is about four times longer than its width. Gravid females and small juveniles are found throughout the year. The species is acyclic; females mature and reproduce throughout the year, unresponsive to seasonal cues, typical of many cave dwelling species (14). One gravid female contained 39 mature ova. Juvenile dispersal is not considered a migration. Captives may live for 10.3 years.

The Texas blind salamander and E. robusta were included in the genus Typhlomolge [4-6]. Although they show extreme specializations for living in underground aquatic systems, they are closely related to other species of Eurycea from Texas and the eastern United States (7,8). The Texas blind salamander has a Rounded Global Status Rank of Critically Imperiled, is listed as Endangered by USFWS, the state of Texas, the U.S. Endangered Species Act (11) and the Federal Government. It is protected at local and national levels (8). It has an extremely restricted distribution within a very fragile subterranean ecosystem in Texas; the aquifer is threatened by water depletion and potential contamination. It is sensitive to changes in water quality and thus vulnerable to groundwater pollutants (13) and falling groundwater levels from increased pumping to support residential and commercial development. Overcollecting in the 1960s may have reduced populations in accessible locations. The salamander is not a resource for humans. Individuals still appear common in outflows of Diversion Spring, a pipe that carries outflows from the Edwards Aquifer at San Marcos Springs. Numbers collected vary widely each year and most may be adults or juveniles (12).

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