San Marcos Salamander
© 2008 Sara Weinstein (1 of 1)
Country distribution from AmphibiaWeb's database: United States
Eurycea nana Bishop, 1941(a)
Paul T. Chippindale1
1. Historical versus Current Distribution. San Marcos salamanders (Eurycea nana) were described from outflows of San Marcos Springs in the city of San Marcos, Hays County, Texas, by Bishop (1941a). Some authors (Sweet, 1978a; Dixon, 1987) also have considered the population of Eurycea at Comal Springs, Comal County, to be this species, but morphological and molecular evidence strongly reject this hypothesis (Chippindale, 2000; Chippindale et al., 1998, 2000). Their historical distribution probably is similar to their current distribution, although San Marcos Springs has been heavily modified by humans in the past century to form a small lake. Salamanders occur throughout much of this lake and extend about 150 m into the most upstream portion of the San Marcos River (Nelson, 1993). Based on phylogenetic analyses, E. nana appears to be the sister taxon to the southeastern Edwards Plateau subgroup of Texas Eurycea (Chippindale, 1995, 2000; Chippindale et al., 2000). Although Schmidt (1953) regarded this taxon as a subspecies of Texas salamanders (E. neotenes), few others (and no recent authors) have followed this approach. Molecular and morphological data strongly support their recognition as a distinct species (Chippindale, 1995, 2000; Chippindale et al., 1998, 2000).
2. Historical versus Current Abundance. Extremely abundant within their severely limited range. Population densities are estimated to be about 116–129 individuals/m2 in vegetation mats (Tupa and Davis, 1976; Nelson, 1993). The entire population has been estimated to be about 53,200 individuals in vegetation mats and suitable rocky substrates (U.S. F.W.S., 1996b).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Unlikely to occur.
ii. Breeding habitat. A subset of adult habitat.
i. Egg deposition sites. Eggs have never been observed in the wild. In captivity, ovipositioning has occurred on aquatic moss, filamentous algae, rocks, and glass marbles.
ii. Clutch size. In captivity, an average of 33 eggs/female has been oviposited during a single egg-laying event. Egg size is about 1.5–2.0 mm (Tupa and Davis, 1976). Eggs hatched at 16–35 d post oviposition; total lengths of larvae were 9–12 mm.
C. Larvae/Metamorphosis. This species is paedomorphic, and natural metamorphosis is unknown. Transformation has been induced artificially through use of thyroid hormone (Potter and Rabb, 1960).
D. Juvenile Habitat. Probably similar to adult habitat.
E. Adult Habitat. Completely aquatic. Found in mats of blue-green algae (Lyngbya sp.), under rocks, and in gravel substrate at water depths of < 1 m to several meters. Water temperature is relatively constant at approximately 22 ˚C throughout the year; experimental studies show a critical thermal maximum of 36–37 ˚C (Berkhouse and Fries, 1995).
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Aestivation is unknown.
I. Seasonal Migrations. Very unlikely to occur.
J. Torpor (Hibernation). Active throughout the year.
K. Interspecific Associations/Exclusions. Little known; fountain darters (Etheostoma fonticola) are common in the same habitats in which this species is found.
L. Age/Size at Reproductive Maturity. Tupa and Davis (1976) noted size at sexual maturity as 19–23.5 mm SVL for males and 21 mm SVL for females. In captivity, eggs were first observed in females at 250 d of age.
M. Longevity. At least 3.7 yr in captivity.
N. Feeding Behavior. Prey consists primarily of invertebrates, particularly chironomids and amphipods (Tupa and Davis, 1976). Oligochaete worms, snails, and zooplankton also are fed in captivity.
O. Predators. Suspected predators include catfishes, centrarchid fishes, and crayfishes (Tupa and Davis, 1976).
P. Anti-Predator Mechanisms. Secretive. Although tails do not autotomize, individuals sometimes exhibit partially missing or partially regrown tails and limbs.
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. The entire population of San Marcos salamanders has been estimated to be about 53,200 (U.S.F.W.S., 1996b). They are listed as Threatened both by the State of Texas (www.tpwd.state.tx.us) and the Federal Government .
1Paul T. Chippindale
2Joe N. Fries
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 11 Nov 2019.
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