Roberts' False Brook Salamander
© 2014 Dr. Joachim Nerz (1 of 15)
Pseudoeurycea robertsi, or Roberts’ False Brook Salamander, has a snout-vent and tail length of approximately 36.8 and 34.5 mm, respectively. It has a flat and broad head. The snout-vent length is 6.2 times that of the head length. The snout is shortened, but reaches over the mouth by approximately 0.5 - 0.7 mm. There is no canthus rostralis. Its nostrils are close to the anterior point. The distance between the nostrils is equal to the interorbital width, both of which are slightly greater than the eyelid width. The loreal region is flatter than the rest of the head. The eye length is about 20% longer than snout length. The posterior ends of each eyelid fits under a skin fold. However, the occipital region is slightly swollen. Just underneath the nostrils is a round swelling near the lip. Roberts’ False Brook Salamander exhibits an almost straight upper jaw edge outline. Pseudoeurycea robertsi exhibits a strong nuchal fold across the ventrum of the neck. A groove from the nuchal fold to the dorsal surface runs slightly forward and joins the groove from the opposite side. A short groove runs vertically from near the corner of the mouth on the lateral surface and across the specimen to the dorsal surface. This groove is intersected by another groove that approaches the nuchal groove, at which it terminates (Taylor 1938).
The dorsal skin of both the head and body are minutely pitted. In total, P. robertsi has 13 costal grooves that appear dim on the axilla. The upper areas of the wrinkly spaces between grooves indicate a sinuous groove running lengthwise. The tail is compressed from the sides. At its base, the tail constricts, and the folds between grooves near the tail appear wrinkly. The tail is slightly shorter than the head and body (Taylor 1938).
When the well developed limbs of P. robertsi are adpressed, each digit is separated by a distance of, at most, one costal fold. Digit webbing is absent. Each finger is flat and has rounded, inflated disks for fingertips, except for the first, which does not have a disk on its fingertip. The relative finger formula is: I < IV < II < III, whereas the relative toe formula is: I < V < II < IV < III (Taylor 1938).
The medium-sized P. robertsi is related to Pseudoeurycea leprosa but can be differentiated by physical appearance. Pseudoeurycea robertsi has a slightly more robust body and a broad, orange stripe that runs along the dorsal surface of the entire body and tail in comparison. Additionally, P. robertsi possesses significantly larger limbs and toes, has no webbing between its toes, and a shorter distance between limbs adpressed along the body (two costal grooves in P. leprosa). Its tail is shorter but almost as long as the head and body. Pseudoeurycea robertsi has a head that is longer than it is wide: the body length is 5.7 times longer than the head whereas body length is 6.2 times longer the width of the head (Taylor 1938). Despite morphological and genetic differences, Pseudoeurycea longicauda was previously referred to as P. robertsi. Tail length is longer and head width is smaller in P. longicauda than in P. robertsi (Lynch et al. 1983).
Coloration is not specified as in life or preservative, but is implied to be in preservative. The species is known for an irregularly patched, broad, orange-reddish dorsal stripe that stretches from the specimen’s head to tail tip with brownish lavender sides. Orange-brown spots can be observed on the head and sides below a grey color. In Taylor (1938), the specimen is described as having been discolored such that the sides and abdomen were deep brown, implying the color description is of a specimen in preservative. The ventral side of the specimen’s hands and feet are spotless (Taylor 1938) In life, the ventrum of the belly and chin is a uniform gray-black (Lynch et al. 1983).
Each paratype is similar in physical character to the holotype but coloration and patterning vary. Physically, adults have different proportions than juveniles. The tail length is shorter relative to head and body length in adult specimens, and the limbs are longer relative to head and body length in adult specimens. One male specimen collected differed from others in having a more truncated snout, larger swelling under the nostrils, and a pronounced chin gland near the lower jaw tip. In males, skin protrusions are observable near the anal slit, as opposed to the fold seen in female specimens. In terms of coloration, on the tail of some specimens, the dorsal stripe breaks up into spots, and the stripe itself may either be brown or faun (Taylor 1938). A 2012 survey further established that coloration varies in relation to elevation with variation increasing with decreasing elevation. Specimens observed in higher elevations maintained a constant pattern while specimens from lower elevations possessed higher variability (Bille 2012).
Distribution and Habitat
Pseudoeurycea robertsi occupies an area of just 8 km2 in Nevado de Toluca, Mexico (IUCN 2016) and can be found in both open areas of pine-fir forest as well as dense and humid parts of the forest at elevations between 2900 and 3600 meters (Bille 2012).
Life History, Abundance, Activity, and Special Behaviors
Little is known of P. robertsi habits and activity. Out of the four salamander species that reside in Nevado de Toluca, P. robertsi is the most abundant. While P. robertsi can be found in somewhat open areas of pine-fir forest, they are more abundant in dense and humid parts of the forest. Specimens were found on the ground under rocks and logs. Bark from fallen stumps and logs also served as shelters for some specimens (Bille 2009, IUCN 2016).
Roberts’ False Brook Salamander reproduces by direct development (IUCN 2016).
Trends and Threats
Pseudoeurycea robertsi is one of the most threatened Mexican amphibian species due to its small distribution, loss of genetic diversity, land use change, and change in protections. Although P. robertsi occupies a small area, it is common within that area. (Alvarez et al. 2010).
More specifically, higher rates of inbreeding caused by smaller population size has led to a loss of genetic diversity, threatening short term survival (Sunny et al. 2019).
The species' habitat is threatened by land use change set off by reduced protections. Commercial logging is legally allowed under the reduced protection status of the Nevado de Toluca Volcano (Sunny et al. 2019). Additionally, agriculture, livestock rearing, and logging has completely deforested the eastern and northern slopes (Bille 2012, IUCN 2016). Housing, urban development, solid pollution, tourism, and recreation are also causing habitat degradation. Confirmed population declines have already been observed in a locality near Buenavista. However, the species is not severely fragmented (IUCN 2016).
Possible reasons for amphibian decline
General habitat alteration and loss
There are two genetically distinct populations of P. robertsi based on phylogenetic analysis on cyt b mtDNA using Bayesian Inference and Maximum Likelihood analyses (Sunny et al. 2019).
The species epithet is a dedication to Radclyffe Roberts from the Philadelphia Academy of Sciences, who collected the type specimens and made the journey to the collection site possible (Taylor 1938).
IUCN SSC Amphibian Specialist Group (2016). ''Pseudoeurycea robertsi.'' The IUCN Red List of Threatened Species 2016: e.T59393A53983925. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T59393A53983925.en. Downloaded on 11 November 2019.
Bille, T. (2009). ''Field observations on the salamanders Caudata: Ambystomatidae, Plethodontidae of Nevado de Toluca, Mexico.'' Salamandra, 45(3), 155-164. [link]
Lynch, J.F., Wake, D.B., Yang, S.Y. (1999). ''Pseudoeurycea longicauda.'' Catalogue of American Amphibians and Reptiles, 686, 1-2. [link]
Sunny, A., Duarte-deJesus, L., Aguilera-Hernández, A., Ramírez-Corona, F. (2019). ''Genetic diversity and demography of the critically endangered Roberts' False Brook Salamander Pseudoeurycea robertsi in Central Mexico.'' Genetica, 147, 149-164. [link]
Taylor, E.H. (1938). "Concerning Mexican salamanders." University of Kansas Scientific Bulletin, 25, 259-312.
Written by: Leighton Pu (2019-12-05)
Edited by: Ann T. Chang (2019-12-17)
Species Account Citation: AmphibiaWeb 2019 Pseudoeurycea robertsi: Roberts' False Brook Salamander <https://amphibiaweb.org/species/4187> University of California, Berkeley, CA, USA. Accessed Apr 13, 2021.
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Citation: AmphibiaWeb. 2021. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 13 Apr 2021.
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