Barred Tiger Salamander
Ambystoma mavortium Baird, 1850
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 populations have resulted from its introduction from its 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 in some environments. The Arizona Tiger Salamander, Ambystoma mavortium nebulosum Hallowell, 1852 is distributed on the Mogollon Plateau, its vicinity, and nearby outlying ranges of central Arizona and adjacent 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. The known populations are mostly positioned between these two rivers, and the salamanders 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 proper; only A. t. stebbinsi is known to occur in the southern section of the drainage into the Gila River.
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 speckle. 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 upperparts that are uniformly gray, brownish, or brownish-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 lives 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). 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). The distribution of A. mavortium stebbinsi in Mexico has been and remains uncertain since it was first described from Arizona. However, Hossack et al. (2016) documented the presence of 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 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 common 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 of the seven sampled stock tanks. To avoid damaging fragile habitat, they did not seine the ciénega where a salamander was collected in 1990. They collected larvae and adult animals in the stock tanks No salamanders seemed sick at any of the other tanks sampled.Sonora Tiger Salamanders have not been collected from non–human-modified habitats, but A. t. stebbinsi presumably occupied natural cienegas (marshes) that were undisturbed prior to European settlement (Jones et al., 1988, 1995). In this now anthropogenically dominated by cattle ranching and the salamander survives only in cattle tanks.Note that Ambystoma mavortium utahensis Lowe is no longer considered valid however it still appears on some faunal lists for Grand Canyon National Park. This is probably due to Lowe’s (1955:247) 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.
Reproduction occurs after winter rains trigger a migration of terrestrial adults from overwintering sites to breeding ponds. Sonoran Tiger salamanders deposit gelatinous-coated eggs laid in water. Sonora Tiger Salamanders begin breeding 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 under water, and like other ambystomid salamanders the male deposits spermatophores (capsules of sperm) and the female picks them up and inserts them into her reproductive track using her rear legs. After fertilization, the female lays a clutch of 200–2000 eggs and attaches them to submergent vegetation, or some other submerged substrate. The eggs may be laid individually or in gelatinous masses of up to 50 eggs. 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 and between 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).Following hatching, Sonoran Tiger Salamander larvae 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 in the absence of 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 items including zooplankton, ostracods, aquatic insect larvae and adults, mollusks, annelids (oligochaetes, leeches), and crayfish, as well as anuran tadpoles, small fishes, and conspecifics (Little and Keller 1937; Gehlbach 1965; Black 1969b; Buchli 1969; Dodson 1970; Dodson and Dodson 1971; Wilbur 1972; Rose and Armentrout 1976; Sever and Dineen 1978; Brophy 1980; Zaret 1980; Collins and Holomuzki,1984; Lannoo and Bachmann 1984a; Leff and Bachmann 1986; Holomuzki and Collins 1987; Zerba and Collins 1992; Brunkow and Collins 1996). Smaller larvae eat smaller prey, larger larvae eat larger prey. 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 to feed on pelagic zooplankton (Rose and Armentrout, 1976; Lannoo and Bachmann, 1984b) and other smaller prey (Lee and Franz 1974; Brophy 1980; Tyler and Buscher 1980). The kinematics of prey capture by Ambystoma larvae were described by Hoff et al. (1985), Shaffer and Lauder (1985), and Reilly et al. (1992). Cannibal morph larvae occur ln tiger salamanders. Cannibal morphs tend to eat larger prey than typical morphs. In populations of Barred Tiger Salamanders, cannibal morphs may prefer to prey on conspecifics (Rose and Armentrout 1976; Collins and Holomuzki 1984; Holomuzki and Collins 1987; Pfennig et al. 1994). Large typical larvae may also be cannibalistic (Crump 1983; Lannoo et al. 1989). The diets of neotenic adults generally resemble that of large larvae (Sprules,1972; Norris 1989).
Boeckman and Whiteman (2018) investigate the role of Tiger Salamander larvae in aquatic ecosystems to determine if they replace the role of the Colorado River Cutthroat Trout a top predator that has been extirpated from much of its range as the result of human disturbance. In western US beaver ponds, the Arizona Tiger Salamander (Ambystoma mavortium nebulosum) often become the top aquatic predator in the absence of fish. Field data for tiger salamanders and published accounts of various salmonid species both species are characterized by size-structured populations with ontogenetic shifts in a generalist diet, the trophic position of A. m. nebulosum is lower than reported values for large salmonids. This lower trophic positioning suggests that salamanders are likely to be functionally complementary with only the smallest size classes of salmonids.
Age at sexual maturity is influenced by temperature, food supply, water conditions, crowding, and subspecies. Time to maturation can be as short as five months in ephemeral pools or three years in subalpine lakes. The events that trigger breeding in branchiate adults are poorly known. Different subspecies have different breeding seasons. Time to hatching is temperature dependent. Eggs laid in cold water take longer to develop. Egg mortality may result from freezing, desiccation, predation by adult salamanders, fish, or aquatic invertebrates. The aquatic larvae hatch and grow with gills, and then mature as one of several morphs: gilled aquatic adults (branchiate adults), neotenes, paedomorphs or they metamorphose into terrestrial salamanders without gills.
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 experimentally exposed and tested 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, and its future survival is dependent 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 to 1999, half of the 53 populations now known were discovered.Prior to the 20th century human influence on the landscape, the San Raphael Valley contained many more cienegas and vernal pools than it does at present. 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 are now dependent on humans to maintain the habitat. Cattle ponds may also require occasional excavation because they fill in with silt, and pond dams require occasional maintenance. Cattle pond habitats are also vulnerable to extreme weather conditions such as long-term drought and if ponds remained dry for several years, a lack of breeding could lead to extirpation of the salamander population. Cattle ponds can also wash out during storms or floods and may result in 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. The state of Arizona made the collection of tiger salamanders in south central Arizona illegal because of the difficulty in identification of the three subspecies known from the state and for the potential genetic damage to the native Sonoran Tiger Salamander. The Sonoran Tiger Salamander is listed as endangered under the Endangered Species Act (US Fish and Wildlife Service 2002).Fossil Record. Mead (2005) summarized the fossil record of the tiger salamander is a late Holocene record for Bida Cave, Grand Canyon, Arizona. Specimens from Show Low are not precisely dated; however, they were recovered with 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 greater than 172,000 yr B.P.Taxonomy. This species has had a long, confusing, and difficult taxonomic history. It has been described twelve times and has at least 22 different combinations of names. Shaffer and McKnight (1996:430) recognizing a broad zone of hybridization between mavortium and tigrinum noting that away from the hybrid zone, each maintains its historical integrity. 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 (1967) considered the holotype as uncertain, suggesting that USNM 3990 could be the holotype and that it was collected by LeConte. 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).The distribution is mostly restricted to the Colorado River Basin, it does not occur in the tributary Gila River Basin and its status in the Little Colorado system is uncertain. In Arizona it is primarily in drainages which flow directly into the Colorado River without entering the Little Colorado or Gila Rivers, such as tributaries to the San Juan River of southern Utah and Tapeats Creek of southern Utah and northern Arizona. Hence there appears to be rather clear-cut though not complete segregation of A. t. utahense and A. t. nebulosum in the basin of the Colorado River in Arizona.
Three subspecies of Barred Tiger Salamanders occur in Arizona (A. m. mavortium, A. m. nebulosus, and A. m. stebbinsi, but only the last one is likely native to the state, and a second appears to be a hybrid between the native populations and individuals introduced from one or more localities outside of the state. The Sonoran Tiger Salamander, Ambystoma mavortium stebbinsi (Lowe, 1954) occurs only in the San Raphael Valley between the Huachuca and Patagonia Mountains of southeast Arizona. The Sonoran Tiger Salamander, A. m. stebbinsi, is considered a distinct subspecies in much of the historic literature. However, it is likely a product of hybridization between the introduced Barred Tiger Salamander and the Sonoran Tiger Salamander.