Animal Diversity Web

Geographic Range

The San Marcos Salamander is endemic to the source of the San Marcos River in Hays County, Texas. Distribution for Eurycea nana is extremely limited, with populations being found in ranges of only several hundred feet along this river within close proximity to San Marcos Spring. (Mitchell, 1990)

• Biogeographic Regions
• nearctic
  • native

Habitat

This salamander is characteristically found in shallow, alkaline springs carved out of limestone with sand and gravel substrates. The thick moss and algae that cover the shallow pools around the springs provide and excellent habitat for Euryca nana to not only find food for itself, but also to keep it safe from predators. Water temperature in the San Marcos and Comal Rivers are remarkably stable with temperatures in close proximity to the springs being between 21.0 to 21.5 degrees Celsius. (Tupa and Davis 1976, Mitchell 1990) (Mitchell, 1990; Tupa and Davis, 1976)

• Habitat Regions
• temperate
• freshwater

• Aquatic Biomes
• rivers and streams

Physical Description

One of the lungless salamanders, Eurycea nana averages about 2 inches long, but may reach up to 3.25 inches. It is the smallest of the genus Eurycea. These salamanders are slender, with short limbs, 5 toes on the rear feet, and 4 and the front. Gill fringes are prominent behind the head and there are also 16 to 17 costal grooves. It is light brown on its back, yellowish white ventrally, with pale yellow flecks obvious on the midline. Distinctive large eyes have a dark ring around the lens. Males have more poorly defined mental and caudal hedonic glands than females. Developed, pigmented gills are maintained throughout adulthood, but gases are exchanged almost entirely through cutaneous respiration. The vents of males are lined with papillae, contrasting with the smooth folds in females. This species is voiceless and earless. (Mitchell 1990, Petranka 1998, Bartlett and Bartlett 1999, Tupa and Davis 1976, Herbeck and Larson 1998)

• Other Physical Features
• endothermic
• ectothermic
• heterothermic
• bilateral symmetry

Development

• Development - Life Cycle
• metamorphosis

Reproduction

Males are sexually mature at 19 to 23.5 mm and females when they are longer than 21 mm. There is only vague information on the reproduction of Eurycea nana and eggs have never been found in nature. Strongly acyclic oviposition and the presence of gravid females and very small larvae during every month of the year suggests that breeding occurs year round. There is not a pronounced peak in breeding. As has been observed in artificial habitats, the average egg clutch is 20 and the jelly-covered eggs are usually laid in standing pools with thick vegetation. After a 24-day period in the eggs, larvae-like tadpoles emerge. (Mitchell 1990, Petranka 1998, Tupa and Davis 1976) (Mitchell, 1990; Petranka, 1998; Tupa and Davis, 1976)

• Key Reproductive Features
• iteroparous
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• oviparous

• Breeding season

  Breeding seems to occur year-round.

Behavior

The San Marcos Salamander is typically active in surface vegetation except in extreme winter weather where it stays beneath underwater logs and boulders. It is often found sitting stationary in algal vegetation waiting for prey, which it then quickly grabs and consumes. Predation threats come mostly from local fish. The primary predators are sunfish (Lepomis), but bullhead catfish (Ameiurus melas) and large mouth bass (Micropterus salmiodes) are also potential threats. (Petranka 1998, Tupa and Davis 1976) (Petranka, 1998; Tupa and Davis, 1976)

• Key Behaviors
• natatorial
• motile
• sedentary

Food Habits

Little is known about the foraging behavior of Eurycea nana. It is carnivorous and has been found to feed mostly on amphipods, midge fly larvae, and some aquatic snails (Petranka 1998).

• Primary Diet
• carnivore
  • insectivore
  • eats non-insect arthropods

• Animal Foods
• insects
• mollusks
• aquatic crustaceans

Conservation Status

The San Marcos Salamander has been listed as a threatened species since July 14, 1980. Agricultural and urban development around the springs it inhabits are thought to be the biggest threats. These problems, along with the fact that habitat is extremely limited, are becoming more serious as a rise in the human population in the area has also increased the demand for water in this semi-arid region. Constant groundwater pumping could dry up the San Marcos, Aquarena, and Comal springs that supply water to the San Marcos and Comal Rivers in a matter of years. To help control this growing problem, Hays County has been designated a critical habitat. Although threatened, the population seemed stable with a count of 17,000-21,000 recorded in 1984. (Mitchell 1990)

• IUCN Red List

  Vulnerable
  More information

• US Federal List

  Threatened

Other Comments

Many aspects of the behavior and life of the San Marcos Salamander are poorly known and are under research at this time.

Contributors

Stefanie Pennington (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

References

Bartlett, P., R. Bartlett. 1999. A Field Guide to Texas Reptiles and Amphibians. Houston, Tx: Gulf Publishing Company.

Herbeck, L., D. Larson. June 1999. Plethodontid Salamander Response to Silvicultural Practices in Missouri Ozark Forests. Conservation Biology, 13(3): 623-632.

Mitchell, R. 1990. WWF Guide to Endangered Species. Washington, D.C.: Beacham Publishing, Inc.

Petranka, J. 1998. Salamanders of the United States and Canada. Washington, D.C.: Smithsonian Institution Press.

Tupa, D., W. Davis. 1976. Population Dynamics of the San Marcos Salamander, Eurycea nana Bishop. The Texas Journal of Science, 27: 179-194.