Tarahumara Salamander (Ambystoma rosaceum)
Tarahumara Salamander. Photo by Cecil Schwalbe.
There are but three members belonging to the group of caudate amphibians that occur within the herpetofauna of the 100-mile circle. This lack of species richness however, does not necessarily equal a lack of charisma or glorious color patterns nor even mystique (Bezy et al. 2004). Tarahumara Salamanders (Ambystoma rosaceum) occur north from Zacatecas, Mexico, along the western flank of the Sierra Madre Occidental to the Sierra El Pinito near Nogales, Sonora; a mere 28 tantalizing kilometers (17 miles) from the Arizona border where they, while amongst the high pines and the ever-present narcotraficantes, and like much of the Sonoran herpetofauna, receive little attention.
The range of Ambystoma rosaceum in Sonora most often coincides with high elevation forests of the Sierra Madre Occidental. However, many of the state’s interior or ‘Sky Island’ ranges also support this species. Here it can be found amongst the same shaded, boulder strewn canyons and deep plunge pools occupied by Lithobates tarahumarae, the Tarahumara Frog (Hale 2001). Unlike the closely related and geographically adjacent Ambystoma tigrinum, permanent or semi-permanent water appears to be an important ecological factor in the distribution of the northern-most populations of A. rosaceum. This may also at least partially explain its absence from Arizona. The Sierra El Pinito, representing the northern-most locality for this species, is a high, mesic range with several steep canyons that usually contain water throughout the arid pre-monsoon months of May and June (S. Hale pers. comm.).
Other northern ranges, such as the Sierra de los Ajos (the highest range in Sonora and also quite close to the Arizona border) possess both similar habitat and Tarahumara Salamanders. As one moves south, precipitation and the diversity of habits occupied increases. Van Devender (1973) documented its occurrence in montane grassland, Hale (2001) has collected A. rosaceum in foothills thornscrub, and the author has observed it in tropical deciduous forest.
Perhaps the most interesting aspect of this species is its striking larval color pattern that is unique among ambystomatid salamanders. Witnessing these larvae in a clear mountain pool is an unforgettable experience. Numerous black markings create a wonderful mosaic against a golden dorsal ground color. Bright red gill rakers provide further sparkling contrast. Hatchling larvae can be quite small ranging 0.9-3.5 cm (.3-1.3 inches) snout-vent length (Anderson 1978), while post-hatchling larvae can attain the rather large size of 12-15 cm (4.7-5.9 inches) total length (Hale 2001). Neotenic forms have also been documented in this species (Anderson 1978).
Adults are a moderately sized Ambystomatid salamander reaching a maximum total length of 15.2 cm (6 inches) (Anderson 1978). Some individuals may possess numerous yellow or white colored spots, while others may possess only faint spotting. Both of these morphs are set against a black or dark brown dorsal ground color. Mature A. rosaceum are known to be terrestrial (Webb 1978); however, observing a mature individual in the field appears to be an infrequent occurrence in Sonora. While conducing field research as part of an ongoing study during several wet nights within the heart of their range and habitat, no adults have been seen (pers. obs.). Moreover, many museum collections are comprised mostly of larval forms (personal observation).
The taxonomy of A. rosaceum has been debated for decades. Taylor (1941) described the type specimen from Mojárachic, Chihuahua along with another very similar species, A. fluvinatum. Subsequent work by Shannon (1951) resulted in the creation of three additional rosaceum subspecies. Then, in his description of the life history and systematics of A. rosaceum, Anderson (1961) removed all subspecies of A. rosaceum and synonymized A. fluvinatum with A. rosaceum. By 1983, Shaffer had investigated the biosystematics and suggested A. rosaceum is composed of two recently diverged lineages that form isolated northern and southern populations. In 1996, Shaffer and McKnight publish a phylogeny of the tigrinum complex concluding once again that A. rosaceum is composed of two allopatric populations. And finally, in the year 2000, nearly 60 years after Taylor introduced A. rosaceum to science, Highton, in the monumental publication; The Biology of the Plethodontid Salamanders, suggested that Shaffer and McKnight’s 1996 phylogenetic analysis of the tigrinum complex provides evidence that A. rosaceum is actually comprised of three species. Regardless of the unresolved taxonomic issues that plague A. rosaceum, there is little doubt that those salamanders approaching the Arizona border are unique and should ultimately be described as such.
Due to the lack of a thorough distributional study, the conservation status of A. rosaceum in Sonora is unknown. However, given the plethora of environmental issues that affect the entire flora and fauna of Sonora, it is not unreasonable to assume that the distribution of A. rosaceum has been negatively impacted by the encroachment of these threats.
Thanks to George Bradley for providing access to the University of Arizona Natural History Museum, Amphibian and Reptile Collection and Andy Holycross for providing collection data from the Arizona State University Natural History Museum Division of Herpetology, and Robert Bezy for review of an earlier draft of this paper.
Anderson, J. D. 1961. The life history and systematics of Ambystoma rosaceum. Copeia 1961:371-377.
Anderson, J. D. 1978. Ambystoma rosaceum. Catalogue of American Amphibians and Reptiles 206.1-206.2.
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Hale, S. F. 2001. The status of the Tarahumara Frog in Sonora, Mexico based on a re-survey of selected localities, and search for additional populations. Report to United States Fish & Wildlife Service, Phoenix.
Highton, R. 2000. Detecting cryptic species using allozyme data, pp. 215-242. In R. C. Bruce, R. Jaeger, L. D Houck eds.,The Biology of Plethodontid Salamanders, Kluwer Academic/Plenum Publishers. New York, NY.
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Shannon, F. A. 1951. Notes on herpetological collection from Oaxaca and other localities in Mexico. Proceedings of the United States National Museum 101 (3284):465-484.
Van Devender, T. R. 1973. Populations of Ambystoma tigrinum and A. rosaceum in Chihuahua, Mexico. Journal of Arizona and Nevada Academy of Science 8:34.
Webb, R. G., and C. H. Lowe, Jr. 1977. Amphibians and reptiles of Yepomera, Chihuahua, Mexico. Journal of Herpetology 11:41-50.
Author: Erik Enderson. Published in the Sonoran Herpetologist 2006 19(4):38-40.