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)
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)
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)
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)
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)
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).
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)
Many aspects of the behavior and life of the San Marcos Salamander are poorly known and are under research at this time.
Stefanie Pennington (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
An animal that eats mainly insects or spiders.
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).
breeding takes place throughout the year
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.