Two small fossil vertebrae (MCA 9017-18) dated from the early Jurassic came from the Harvard Gold Springs Quarry of the Kayenta Formation in northeastern Arizona (Holman 2006). Ironically, this is the oldest fossil salamander in North America and possibly the world, and it is from a state with a single known species of extant salamander. The remains were described by Curtis and Padian (1999)
The single salamander species known from Arizona, is the Western Tiger Salamander, Ambystoma mavortium (family Ambystomidae). However, there is circumstantial evidence that one, or possibly two, other species may occur in Arizona.
The Lungless Salamanders (family Plethodontidae) are widespread in the eastern USA but less common in western North America. Salamanders of the Isthmura bellii complex are widespread in central México. They are the largest terrestrial, lungless salamanders, with distinctive coloration – a black background with bold red-orange marks on the dorsum. Most of these salamanders live above 700 m in pine-oak forests. The genus is of biological interest because, like many high-altitude vertebrates it is thought to have direct development, with the females giving birth to young instead of laying eggs, although this needs confirmation. Most species of Isthmura are listed as vulnerable or critically endangered by the IUCN.
Bell’s False Brook Salamander was first described by Gray (1850) as Spelerpes bellii. In a review of the Plethodontidae, Dunn (1926) wrote: “United States: Arizona: Ft. Whipple 3 (U.S.N.M., uncataloged, now lost).” Dunn suggested there were three specimens of this salamander in the Smithsonian from near Ft. Whipple, Arizona but the specimens had been lost.
After Gray’s description, the salamander was moved to the genera Geotriton, Oedipus, Bolitoglossus, Pseudoeurycea, and most recently, Rovito et al. (2015) moved these salamanders to Isthmura.
Lowe (1955:250) noted that no plethodontid salamander populations occurred in Arizona. However, he suggested the discovery of three species (Plethodon vandykei idahoensis, Plethodon neomeixcanus, and Aneides hardyi) in Rocky Mountian coniferous forest habitats indicate that relict populations may also occur in mesic high forest habitats in Arizona (Lowe, 1950). Therefore, it seems reasonable to expect them in such places as the White Mountains of east-central Arizona, the high Coconino Plateau, the higher elevations of the central and northern parts of the state, or in the higher southern mountain ranges such as the Pinaleno Mountains.
In 1964 a population of what was then called Pseudoeurycea bellii was discovered near Yecora, Sonora. This Sierra Madre Occidental locality is about 880 km (550 mi) northwest of the nearest known localities for the species in Nayarit and 770 km (480 mi) southeast of Dunn’s lost USNM specimens from Fort Whipple, Arizona. In 1968, Lowe et al. named the new subspecies P. b. sierraoccidentalis for the Sonora-Chihuahua population based on the reduced dorsal blotches of the new subspecies. In 1987, Tom Van Devender and Peter Holm observed four adults of P. b. sierraoccidentalis in the Ocampo area of Chihuahua. The population became the second locality for the subspecies (Bezy et al. 2004). This left P. bellii in isolated populations in central Mexico’s Sierra Madre Oriental in the states of Tamaulipas, Nayarit, Zacatecas, and Guerrero. Parra-Olea et al. (2005) split these populations into several species.
The Arizona specimens Dunn noted likely represented an undescribed species. that may still maintain populations in the high-altitude pine-oak forests around Ft. Whipple and have simply evaded herpetologists. Or, the population may have been extirpated due to development or natural causes. The question of an Arizona species of Isthmura remains unresolved.
There is second possible plethodontid salamander in Arizona, an alien population of the Large-blotched Ensatina (Ensatina eschscholtzii klauberi) was established in a montane region of Arizona.
Mole salamanders occur from southern Canada to the Mexican Plateau and contain 37 species in two genera. Fossils are known from the Oligocene, about 37.3 Ma, but the molecular clock suggests a more ancient family split from its Eurasian sister family, the Salamandridae, 167 Ma (Kieren et al. 2018). Most mole salamanders have courtship and breeding in the late winter or spring, but a few species reproduce in autumn. Some species are polyploids, having evolved by increasing the number of sets of chromosomes. Larvae may overwinter in ponds, and some species retain larval characteristics, such as external gills and tail fins into adulthood. These larva-like adults are known as paedomorphs or neotenes, and they can reproduce while retaining the larval traits (Blackburn and Wake 2011, Vitt and Caldwell 2013).
The Tiger Salamander, Ambystoma tigrinum was considered the most widespread salamander species in North America by Lannoo et al. (1995), ranging from Southern Canada southward through the United States and into northern Mexico, at elevations up to 3,660 m asl. Still, it was absent from much of the Great Basin, New England, and the Appalachians (Hammerson et al. 2008).
However, Schaefer and McKnight (1996) analyzed the Ambystoma tigrinum complex, using 840 base pairs of mitochondrial-DNA sequence from the rapidly evolving D-Ioop and an adjacent intron. Their samples include populations of the North American distributed species, A. tigrinum, plus all described species of Mexican ambystomatids. They found low sequence divergence (0-8.5%), and most clades were weakly supported. They identified eight reasonably well-defined clades from the United States and Mexico, with the geographically isolated A. californiense from California as the probable sister to the remaining taxa. Their sequence data were incapable of resolving the relationships among these clades. However, the pattern of transitional-site evolution suggests these eight lineages diverged during a period of rapid cladogenesis. They roughly calibrate a molecular clock and identify a few lineages that significantly deviate from the slow baseline rate of 0.5-0.75% per million years. Their data suggested species boundaries for several U.S. and Mexican species need to be altered and that the concept of a continentally distributed, polytypic tiger salamander was invalid. Therefore, the Barred Tiger Salamander, Ambystoma mavortium Baird, 1850 became the name applied to the western North American species. Yet, some literature may still call Arizona Tiger Salamanders Ambystoma tigrinum.
Tiger salamanders were first reported in Arizona when Hallowell described A. nebulosum in 1852 (1853). He initially gave the type locality as New Mexico, later revising it to the San Francisco Mountains of Arizona. Mole salamanders were rediscovered in Arizona’s Parker Canyon in the Huachuca Mountains at an elevation of about 1,500 m ASL by Reed (1951), and their presence was later confirmed by Lowe (1954).
Ambystoma larvae (commonly called waterdogs) have been used as fishing bait for at least 40 years, a 1968 report suggests 2.5 million tiger salamander larvae were sold as bait in the lower Colorado River area alone, totaling $500,000 in a single year (Picco and Collins, 2008).
The Arizona Tiger Salamander, Ambystoma mavortium nebulosum Hallowell, 1852, is distributed on the Mogollon Plateau and the Colorado Plateau and in adjacent New Mexico. In Arizona, most populations are in the basins of the Little Colorado and Gila Rivers, both of which are tributaries of the Colorado River. Known populations are positioned, with rare exception, between these two rivers and are probably more abundant in the Little Colorado drainage system than in that of the Gila. No populations of this race are known from south of the Gila River. Molecular evidence suggests that the Sonoran Tiger Salamander evolved from a hybridization event between the Barred Tiger Salamander (A. m. mavortium) and the Arizona Tiger Salamander (A. m. nebulosa).
Barred Tiger Salamander
Ambystoma mavortium Baird, 1850
Adults can exceed 35 cm (total length), and they are likely the longest terrestrial North American salamander. The dorsum is black, and the snout rounded, the eyes bulge slightly from the head. The tail is laterally compressed.
Three subspecies of Barred Tiger Salamanders occur in Arizona: the Sonora Tiger Salamanders, Ambystoma m. stebbensi; the Arizona Barred Salamanders, A. m. nebulosum, and the Barred Tiger Salamanders, A. m. mavortium. The eggs, larvae, and branchiate adults of the three subspecies are similar in appearance. However, the larvae of the Arizona and Barred Tiger Salamanders sometimes develop into a cannibal morph. This morph has a wider head, enlarged vomerine teeth, and feeds primarily on smaller conspecifics. Cannibal morphs of the A. m. stebbensi are rare. Metamorphosed Arizona Tiger Salamanders have 11–50 irregularly shaped, yellow to olive spots and blotches, often with indistinct edges (Stebbins 1985), on a dark dorsal ground, with a similar pattern on the head and tail. Metamorphosed Barred Tiger Salamanders have large, distinct, yellow transverse bars or spots on a dark dorsum that sometimes encroach on the dark venter. The reticulate pattern of the Sonora Tiger Salamanders is not seen in the other two subspecies. Many metamorphosed Sonora Tiger Salamanders do not have the reticulate pattern and are indistinguishable from the Barred Tiger Salamanders. The Sonora Tiger Salamanders possess genetic characteristics that resemble Barred Tiger Salamanders and, in other respects, resemble Arizona Tiger Salamanders. A likely explanation for this pattern is a hybridization event between Arizona and Barred Tiger Salamanders in the distant past (Jones et al. 1995).
Metamorphosed terrestrial Sonora Tiger Salamanders have a pattern that can be reticulate with a network of pale pigment combined with pale spots, on a dark black or brown background, to a pattern of large, well-defined pale or yellow spots or transverse bars, some of which extend on to the black venter. Metamorphosed Sonora Tiger Salamanders measure from about 45–150 mm in SVL. Branchiate adults’ dorsum is gray to olive and an off-white to yellow ventral surface. Three external gills are on each side of the head, and they measure 65–165 mm SVL. Male adult salamanders can be distinguished by two black folds of tissue (cloacal folds) on the caudal side of the male’s cloaca. Larvae have a gray dorsum and only scattered pigment on the ventral surface. They have external gills and hatch without legs, but the limbs appear early in development. An individual can pass through up to six distinct morphs during its lifetime. The morphs are: gilled adults, cannibalistic gilled adults, normal transformed adults, cannibalistic transformed adults, large, transformed adults, and small transformed adults. The cannibal morph occurs in four of the subspecies and is characterized by a broad head, large skull, and an extra row of pre-vomerine teeth. Additionally, the cannibal morphs reach a larger adult size than the other morphs. Large and small morphs depends upon whether the breeding site is a seasonally ephemeral pool or a larger, permanent body of water. The small morphs occur in the ephemeral pools, transform at a smaller size, and reach a smaller adult size. Adult terrestrial morphs may reach 165 mm SVL. However, paedomorphs may reach 381 mm in total length. McLean et al. (2016) found evidence that the cannibal morphs may not only respond to the density of conspecifics, but they may develop in ponds that have fish competitors, specifically the Flathead Minnow which has a diet like that of larval Ambystoma mavortium.
Distribution and Habitat. In Canada it ranges from Alberta, British Columbia, Manitoba, and Saskatchewan southward through the USA. It occurs in Arizona, California, Colorado, Idaho, Kansas, Minnesota, Montana, North Dakota, Nebraska, New Mexico, Nevada, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington, and Wyoming. It ranges southward into Sonora, Mexico. Three subspecies have been reported to occur in Arizona. It occurs in Semi-desert Grassland, Plains and Great Basin Grasslands, Interior Chaparral, Great Basin Conifer Woodland, Petran Montane Conifer Forest, Subalpine Grassland (Brennan and Holycross 2006)
The Barred Tiger Salamander, Ambystoma mavortium mavortium Baird 1850 ranges from northern Utah and Wyoming southward into Arizona and New Mexico southward to the international border. In Arizona, it stays north of the Mogollon Rim. The Arizona population results from its introduction from larvae use as fishing bait (Stebbins 1985). Vaughan (1961) has reported this salamander in the burrow of the Plains Pocket Gopher (Geomys bursarius), a reminder that this species may depend upon mammal burrows for overwinter survival at some locations.
The Arizona Tiger Salamander, Ambystoma mavortium nebulosum Hallowell, 1852 inhabits the Mogollon Plateau, its vicinity, and nearby outlying ranges of central Arizona and New Mexico. It is restricted to the Colorado River Basin, in so far as now known. In Arizona, most populations are in the basins of the Little Colorado and Gila Rivers, both of which are tributaries of the Colorado River. Known populations are primarily between these two rivers, and the salamanders are probably more abundant in the Little Colorado drainage system than the Gila. No populations of this race are known from south of the Gila River proper; only A. t. stebbinsi occurs in the southern section of the drainage.
Dorsal surfaces are usually olive-gray to dark gray with many small black, dark green to yellowish spots on back, tail, limbs, and head, forming from 11 to 50 irregular markings between lower flanks. Individuals in northwestern New Mexico are green with a yellow speckling. Those from Colorado are more robust, sometimes uniformly dark gray to blackish or with black spots. The ventral surface is often marbled with black. This population includes Ambystoma mavortium utahense Lowe, 1955, of Uintah County, in eastern Utah, characterized by the absence of dorsal spots on the upper parts uniformly gray, brownish, or brown-black. Sometimes black spots in transformed individuals. In the Rocky Mountains, from southeastern Idaho to Arizona, reaching Chihuahua (Mexico), up to 3,350 m. This populations live in a high elevation area of Colorado (over 3,000 m), in Conejos Counties (approximately 50 km west of Alamosa City) and San Juan. In New Mexico, breeding was observed in a farm pond between September and April (in Petranka, 1988). In the high elevations of Colorado breeding begins in June. Cannibal morph larvae are more common than other subspecies.
The Sonoran Tiger Salamander, Ambystoma mavortium stebbinsi Lowe, 1954 is distributed in the San Rafael Valley (approximately 567 km2), between the Patagonia and Huachuca Mountains, and south of the Canelo Hills, Arizona (Hossack et al. 2016). Distributing A. mavortium stebbinsi in Mexico has been and remains uncertain since it was first described from Arizona. However, Hossack et al. (2016) documented what is likely to be A. m. stebbinsi living in stock tanks in northern Sonora, Mexico.
The natural habitat of Ambystoma m. stebbinsi in Arizona was likely the ciénegas or marshes that formed around springs. In the San Rafael Valley and the surrounding mountain ranges, its elevational range is 1,418 –1,897 m ASL, and its habitat is primarily grasslands. The Sonoran Tiger Salamander uses cattle tanks to reproduce, although historically, it inhabited cienegas, which have mostly disappeared from its range (Hossack et al. 2016).
As their family name (Mole Salamanders) suggests, ambystomid salamanders spend much of their adult life underground in burrows. They may excavate these themselves or use burrows made by other animals. In Sonora, Mexico Hossack et al. (2016) found salamanders in six sampled stock tanks. To avoid damaging fragile habitats, they did not seine the ciénega where a salamander was collected in 1990. Instead, they collected larvae and adult animals in the stock tanks No salamanders seemed sick at the other tanks sampled.
Sonora Tiger Salamanders have only been collected from human-modified habitats, but A. t. stebbinsi presumably occupied natural cienegas (marshes) undisturbed before European settlement (Jones et al., 1988, 1995). Today, the salamander survives only in cattle tanks.
Ambystoma mavortium utahensis Lowe is no longer valid; however, it still appears on some faunal lists for Grand Canyon National Park. This is probably due to Lowe’s (1955:247) description of distribution.
Reproduction occurs after winter rains trigger a migration of adults from terrestrial overwintering sites to breeding ponds. Sonoran Tiger Salamanders deposit gelatinous-coated eggs laid in water. Sonora Tiger Salamanders breed as early as January and lasts through April and early May. Breeding after monsoon rains in July and August is uncommon. Females ready to reproduce have swollen, red cloaca. Terrestrial adults, which are often away from water for most of the year, migrate to ponds to breed. Gehlbach et al. (1969) found that Arizona Barred Salamanders aggregated when damp spots under cover became localized. Branchiate adult salamanders do not leave the water.
Most Ambystoma species usually return to breed in the ponds where they were raised (Semlitsch and Pechman 1985; Madison and Farrand 1998). However, there is little known on breeding site fidelity in the Sonoran Tiger Salamander. Courtship takes place underwater, and like other ambystomid salamanders, the male deposits spermatophores (capsules of sperm). The female picks them up and inserts them into her reproductive tract using her rear legs. After fertilization, the female lays a clutch of 200–2000 eggs and attaches them to submerged vegetation or some other submerged substrate. The eggs may be laid individually or in gelatinous masses of up to 50. Eggs hatch in 19 to 50 days, depending upon conditions at the breeding site.
Incubation times for Barred Tiger Salamanders are eight and a half days at 25 °C (Webb and Rouche 1971; see also Petranka 1998). Incubation times for Arizona tiger salamanders range from six and a half days at 19 °C to 14-21 days in natural wetlands (Tanner et al., 1971; see also Petranka 1998). Hatchlings are 9-10 mm TL for Barred Tiger Salamanders (Webb and Rouche 1971), and 9-14 mm for Arizona Tiger Salamanders (Tanner et al. 1971).
Sonoran Tiger Salamander larvae hatch and can reach the minimum size necessary to metamorphose in two months. However, because many San Raphael Valley localities with salamanders hold water all year, larvae stay in the water longer before metamorphosing. Or develop into branchiate adults instead of metamorphosing.
Larval Feeding. Tiger salamander larvae are gape-limited, size-selective feeders. They remain size-selective without visual and olfactory cues, suggesting that nocturnal feeding is mediated by lateral line mechanoreceptive and electroreceptive organs (Lannoo, 1986, 1987). Larvae are dietary generalists, feeding on a wide range of invertebrate prey (Ghioca-Robrecht and Smith 2008).
Larvae will gulp air to fill their lungs and acquire buoyancy (Branch and Altig 1981. Lannoo and Bachmann 1984b) to maintain a position in the water column while they feed (Rose and Armentrout, 1976). The kinematics of prey captured by Ambystoma larvae were described by Reilly et al. (1992).
Boeckman and Whiteman (2017) found the role of Tiger Salamander larvae in aquatic ecosystems is ecologically similar to the Colorado River Cutthroat Trout. The fish is a top predator extirpated from much of its range due to human disturbance. In western USA beaver ponds, the Arizona Tiger Salamander often becomes the top aquatic predator absent fish.
Disease. Christman and Jennings (2018) sampled 3,190 individuals of New Mexico amphibians representing 21 of the 27 amphibian species known to occur in New Mexico. Bd was detected in 12 of the 21 species tested. Salamanders (three species) appeared to exhibit lower detection rates than did anurans (nine species). All six ecoregions and all five major river drainages possessed amphibians that tested positive for Bd. Otsuru (2019) found larval Ambystoma could carry Bd.
Conservation. Much of the habitat for the Sonoran Salamander has been destroyed, and today the species uses cattle tanks in desert grassland areas to reproduce. Its future survival depends on these livestock tanks. Standing water from January through June is the most important habitat characteristic. At least three of the 18 colonies described in 1988 were extirpated. However, between 1994 and 1999, half of the 53 populations were discovered.
Before the 20th century human influence on the landscape, the San Raphael Valley contained many more cienegas and vernal pools than it does now. Erosion and arroyo cutting in the late 19th and early 20th centuries resulted in a lower water table and the disappearance of natural standing bodies of water (Hendrickson and Minckley 1984, Hadley and Sheridan 1995). Simultaneously cattle ponds were constructed and the remaining springs and cienegas impounded. Today the small standing water habitats that remain are cattle ponds. Sonoran Tiger Salamanders breed almost exclusively in these cattle tanks instead of natural habitats. This does not necessarily threaten the populations. Sonora Tiger Salamanders have successfully bred in cattle ponds for decades, but the salamanders depend now entirely on humans to maintain their habitat. Cattle ponds may also require occasional excavation because they fill in with silt, and pond dams require periodic maintenance. Cattle pond habitats are also vulnerable to extreme weather conditions such as long-term drought, and if ponds remain dry for several years, a lack of breeding could extirpate the salamander population. Cattle ponds can also wash out during storms or floods and may cause the loss of parts of the small populations.
Other possible threats to the species include disease, predation by introduced non-native fish and bullfrogs, illegal collection for bait by anglers, habitat destruction, reduced fitness due to inbreeding, and increased probability of random extirpation characteristic of small populations. Arizona made the collection of tiger salamanders in south-central Arizona illegal because of the difficulty in identifying the three subspecies known from the state and for the potential genetic damage to the native Sonoran Tiger Salamander. The Sonoran Tiger Salamander is endangered under the Endangered Species Act (US Fish and Wildlife Service 2002).
Fossil Record. The fossil record of the tiger salamander consists of a late Holocene record from Bida Cave, Grand Canyon, Arizona. Specimens from Show Low are not precisely dated; however, they were recovered with a typical Pleistocene fauna such as the extinct peccary, Platygonus. Ambystoma vertebrae and limb bones were common in various units within Papago Springs Cave in southeastern Arizona, including a layer dating to over 172,000 YBP (Mead 2005).
Taxonomy. This species has had a long, confusing, and difficult taxonomic history. It has been described twelve timesand hasat least 22 combinations of names. Shaffer and McKnight (1996:430) recognize a broad zone of hybridization between mavortium and tigrinum noting that each maintains its historical integrity away from the hybrid zone. They wrote, “…and we have no reason to suspect that they will fail to do so in the future. Thus, we support the phylogenetic view (Cracraft 1989) that these are best considered separate species even though they can hybridize.”
Baird (1850:249) (dated 1849) described Ambystoma mavortia based upon the holotype USNM 3990, according to Yarrow, (1882:149). Gehlbach (1967a) considered the holotype uncertain, suggesting that USNM 3990 could be the holotype and that LeConte collected it. Hallowell, (1853:209) described Ambystoma nebulosum based upon syntypes that included USNM 4702a (according to Cochran, 1961:7); ANSP 1294 and USNM 4702a.
Lowe (1954:243) described Ambystoma tigrinum stebbinsi based upon the holotype UAZ 665, from the type locality of J.A. Jones Ranch, in Parker Canyon, southwest side of the Huachuca Mountains, ca. 5,000 feet, Santa Cruz County, Arizona. Lowe (1955:247) gave the distribution as extreme northern Arizona, including part of the south rim area of the Grand Canyon, northwestern New Mexico, western Colorado, extreme southwestern Wyoming, and the Interior Basin and Colorado Plateau in Utah, approximately as mapped by Stebbins (1951: 496).