This mole salamander is the largest land dwelling salamander in North America. It also has the greatest range of any other North American salamander, spreading in range from southeastern Alaska east to the southern part of Labrador, and south throughout all of the United States down to the southern edge of the Mexican Plateau (Indiviglio 1997).

Biogeographic Regions: nearctic (Native )

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

occurs (regularly, as a native taxon) in multiple nations

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Range extends from portions of southern Canada southward through much of the United States and as far south as Puebla, Mexico. Western populations (regarded by some as A. mavortium) and eastern populations (A. tigrinum) meet in the Great Plains region, where their distributions meld. Tiger salamanders are absent from most of the Great Basin, most of the western United States west of the Rocky Mountains, New England, and the Appalachians. They have been introduced in many localities west of the Rocky Mountains. Elevational range extends to about 3,660 meters (12,000 feet).

See Church et al. (2003) for a map of the county distribution of the eastern tiger salamander.

Adult Length 17-33 cm.

The adult tiger salamander is a thick-bodied creature generally with yellow blotches or spots against a black background. Once in a while there will be one with blotches that are tan or olive green in color. The spots or blotches are never in any set shape, size or position. Actually you may even be able to tell its origin by the color and pattern of the background and/or spots (Indiviglio 1997). A. tigrinum has a rather large head and a broad rounded snout. Their eyes are round. The belly is usually yellowish or olive with invading dark pigment. It has about 12-13 coastal grooves (Harding 1997). Males tend to be proportionally longer, with a more compressed tail and longer stalkier hind legs than the females. During the breeding season the males have a swollen vent area. The larvae have a yellowish green or olive body with the dark blotches and a stripe along each side. They also have a whitish belly. As they grow, specimens tend to be grayish or greenish in color, and within a few weeks they start to show yellow or tan spots and gradually merge into the patterns of the adult bodies (Harding 1997).

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Average mass: 9.402 g.

Average basal metabolic rate: 0.00196 W.

Length: 35 cm

The following pertains to metamorphosed adults. Differs from A. MACRODACTYLUM in lacking a distinct dorsal stripe or stripelike row of spots. Differs from A. GRACILE in having distinct dorsal markings and tubercles on the underside of the feet and by lacking parotoid glands and a glandular ridge on the tail. Differs from A. ANNULATUM in lacking a light grayish stripe along the lower side of the body and generally lacking narrow light bands across the body. Differs from A. MACULATUM and A. OPACUM in having large light blotches on the sides. Differs from A. TALPOIDEUM in having sharply defined spots and usually more than 11 costal grooves (vs. 10-11). Differs from all other North American Ambystoma in having tubercles on the soles of the feet. Differs from plethodontid salamanders in lacking a nasolabial groove.

• Terrestrial
• Freshwater

Fully metamorphosed adults lead a terrestrial existance and, depending upon where in the country they are found, some may inhabit forests, grasslands, or marshy areas (Petranka 1998). Tiger salamanders are less dependent on the forest than most other Ambystomids. One general requirement seems to be soil in which they are able to burrow or in which the burrow of other species of other animals might be utilized (Petranka1998). While they are well suited for terrestrial existence in terms of their skin consistency and thickness, they do need to be able to burrow underground in order to seek the proper humidity levels. Another requirement is that they live close enough for permanent access to ponds and othe small waters for their breeding. During dry periods, large numbers of tiger salamanders have been found lying in piles beneath suitable cover or underground (Indiviglio 1997).

Terrestrial Biomes: forest

Comments: Tiger salamanders can be found in virtually any habitat, providing there is a terrestrial substrate suitable for burrowing and a body of water nearby suitable for breeding. Terrestrial adults usually are underground, in self-made burrows or in those made by rodents, shrews, or other animals. In New York, adults on land used wooded areas and avoided grassy areas (Madison and Farrand 1998). At high elevations in the Rocky Mountains, metamorphosed adults commonly occur in ponds throughout the summer. Breeding occurs in a wide range of environments, ranging from clear mountain ponds to temporary, manure-polluted pools in the lowlands, generally in sites where predatory fishes are absent. In the mountains of western Colorado, tiger salamanders are associated with ponds that have silty bottoms, low alkalinity, and no fishes (Geraghty and Willey 1992). In the southeastern U.S., this species breeds in open, grassy, usually temporary, ponds (Jensen et al. 2008). Eggs are attached to submerged objects or pond bottoms.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

May migrate up to at least a few hundred meters between breeding and nonbreeding habitats. In New York, all movements occurred in areas within 300 m of the nearest breeding pond (Madison and Farrand 1998). Migrations often coincide with rainfall. Migrations in New York were facultative; some did not emigrate from ponds during the year of breeding (Madison and Farrand 1998).

The tiger salamander's food source consists of worms, snails, insects, and slugs in the wild; while captive specimens rely on smaller salamanders, frogs, newborn mice, and baby snakes. Tiger salamanders in the wild also tend to eat the same thing as captives, if opportunity presents itself (Indviviglio 1997). The larvae begin feeding on small crustaceans and insect larvae and once grown, they will feast on tadpoles and smaller salamander larvae and even small fish (Harding 1997).

Comments: Adults eat any small animal that can be captured and swallowed. Larvae eat aquatic invertebrates and vertebrates (especially amphibian larvae) as available.

They are efficient predators in their aqautic and subterranean environment, and their prey includes some insect pests.

Tiger salamanders are eaten by badgers, snakes, bobcats, and owls. Larvae are eaten by aquatic insects, the larvae of other salamanders, and snakes.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: Many occurrences.

>1,000,000 individuals

Comments: Total adult population size is unknown but surely exceeds 1,000,000.

Drying of breeding pond may result in total reproductive failure in some years (Semlitsch 1983). May incur heavy egg predation by eastern newt in some areas. See Worthylake and Hovingh (1989) for information on recurrent mass mortality associated with bacterial infection in mountains of Utah; it was suggested that nitrogen augmentation due in part to sheep grazing may be involved.

In New York, frequent predation occurred in small mammal runways, probably by short-tailed shrews (Madison and Farrand 1998).

Comments: As in most other land-dwelling amphibians, most terrestrial activity occurs during and after rains; freezing weather and drought inhibit activity.

Eggs are laid in small pools and hatch within a time period of 19 to 50 days. The larvae remain in the pond until they turn into adults at 2.5 to 5 months of age. Sometimes, adult tiger salamanders remain in the aquatic larval form for their entire lives.

Development - Life Cycle: metamorphosis

Aquatic adult tiger salamanders live up to 25 years in captivity. Normal adults have reached ages of 16 years.

Range lifespan

Status: captivity: 25 (high) years.

Average lifespan

Status: captivity: 25.0 years.

Average lifespan

Status: captivity: 10.3 years.

Ambystoma tigrinum migrates to the breeding ponds in late winter or early spring, usually after a warm rain that thaws out the ground's surface. Males tend to arrive earlier than the females, probably due to the fact that they live closer to the ponds during the winter months. Courtship happens during the night where the males nudge and bump other salamanders. Upon coming across a female, the male will nudge her with his snout to get her away from the other males (Harding 1997). Once away from the other males, the male walks under the females chin, leading her forward and then she nudges his tail and vent area. This behavior stimulates the male to deposit a spermatophore. The female moves her body so that the spermatophore contacts her vent, thus allowing her to take sperm into her cloaca. This behavioral movement continues and produces more spermatophores. The competition for breeding is great in this species and sometimes other males may interupt the courting pairs and replaces the spermatophores with its own. The laying of eggs occurs a night, usually 24-48 hours after the courtship and insemination. They lay the eggs and attach them with twigs, grass stems and leaves that have decayed on the bottom floor of the pond. Each mass can obtain up to 100 eggs (Harding 1997). When large enough, the masses can resemble that of a spotted salamander but the mass of a tiger salamander is less firm and is very fragile if handled. Each female produces anything from 100 to 1000 eggs per season (Harding 1997).

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous

Average time to hatching: 28 days.

Average number of offspring: 37.

Average age at sexual or reproductive maturity (male)

Sex: male: 1460 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 1460 days.

In general, breeding occurs in spring in the north and at high elevations, in winter in the southern U.S., in late winter/spring and/or summer in the Southwest, and in late winter-early spring in the mid-Atlantic states. Typically the female oviposits within two days after picking up a spermatophore. Individual female deposit up to 1,000 eggs. Eggs hatch in about 2-5 weeks, depending on the temperature. Larvae metamorphose in their first or second summer, or they may not metamorphose at all (become sexually mature as gilled larvae). Reproductive success may be highly dependent on seasonal patterns of rainfall and temperature (Mitchell 1991). In South Carolina, reproductive success varied greatly in different years; little or no recruitment occurred during drought periods (Pechmann et al. 1991). Breeding aggregations may include a few or up to several hundred adults.

Populations in the southeastern U.S. have been affected by deforestation and loss of wetland habitats and appear to be declining in many areas. According to studies in the Colorado Rockies done by Harte and Hoffman, acid rain may be responsible for this. Other studies indicate that it might not have anything to do with it (Petranka 1998). Other threats for these salamanders are being hit by cars and polluting of their ponds and habitats.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: NNR - Unranked

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: T5 - Secure

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Intrinsic Vulnerability: Moderately vulnerable

Comments: Populations can recover from drastic declines over a period of a few years, with high recruitment of juveniles. Given normal dispersal distances (see occurrence specifications), recolonization of habitats from which extirpated may be slow to absent if nearby populations within about 0.5-1 km are also extirpated.

Environmental Specificity: Narrow to moderate.

Comments: Species is a generalist with respect to terrestrial habitats, but reproduction is largely dependent on fishless bodies of water.

Global Short Term Trend: Relatively stable to decline of 30%

Comments: Populations in the southeastern United States appear to be declining as a result of deforestation and loss of wetland habitats (Petranka 1998), though quantitative information on recent trends is unavailable. See Collins et al. (1988) for information on status of the subspecies STEBBINSI.

Global Long Term Trend: Increase of 10-25% to decline of 50%

Comments: Quantitative information is not available for most areas, but the long-term trend in most areas likely is of relative stability in population attributes. Significant declines likely have occurred mostly in the extensively cultivated regions of the Great Plains and in the southeastern United States where intensive deforestation and drainage of wetlands have occurred.

This species tends to breed from November to May, and migrates to breeding ponds on rainy nights. Breeding ponds range from vernal pools to clear montane water bodies to temporary, manure-laden lowland pools. Eggs are deposited en masse and are attached to the pond bottom or to submerged objects. Larvae hatch in 10-21 days. Adults can live up to 20 years in captivity but are thought to survive only 1-3 years in the wild (BCRS 2008).

A cannibalistic larval morph exists but is rare and appears to be constrained by pathogen density; cannibalistic larvae prey on sick conspecifics and thus appear to have an enhanced risk of disease in lakes with periodic bacterial blooms (Pfennig et al. 1991; Bolker et al. 2008).

Aquatic larvae live in shallow water, with bright light, while terrestrial adults usually shelter underground in burrows, either self-constructed or made by rodents or other burrowing animals. Larvae have five different types of photoreceptors (two rod types and three cone types, with cones being sensitive to red, blue or UV light); blue cone photoreceptors are lost during metamorphosis, probably an adaptation to the dim light experienced in the terrestrial phase (Chen et al. 2008).

A. tigrinum has been introduced to central California, where it has been found to hybridize with native A. californiense (Riley et al. 2003; Storfer et al. 2004; Fitpatrick et al. 2010).

Comments: Most remaining populations are exposed to low level threats from habitat loss and degradation, though quantitative information is lacking.

Tiger salamanders occur throughout their historical range in the Rocky Mountains and Great Plains of Colorado and adjacent states. They remain easy to find and locally abundant in suitable habitat statewide. Ponds often contain up to several thousand larvae. Recent surveys found no evidence of significant declines in distribution or abundance (Corn, Stoltzberg, and Bury 1989; Hammerson 1989a, 1992; Corn, Jennings, and Muths 1997). In the Rocky Mountains, a local decline in numbers over several years, reported by Harte and Hoffman (1989), turned out to be a temporary fluctuation from which the population subsequently recovered (Wissinger and Whiteman 1992). Hovingh (1986) reported that tiger salamanders remain quite common in aquatic systems in glaciated portions of the Uinta Mountains in northeastern Utah. The widespread creation of small, fishless artificial bodies of water has provided much suitable habitat where previously there was little, and these salamanders have been quick to colonize it (Norris 1973; pers. obs.).

Many mountain lakes formerly inhabited by tiger salamanders now have few or none of these amphibians due to the stocking of trout, which easily consume and deplete the larval populations (e.g., Blair 1951; pers. obs.). Geraghty and Willey (1992) found that fish absence was the most important factor influencing tiger salamander presence in Gunnison County and vicinity, and Corn, Jennings, and Muths (1997) reported that trout and tiger salamanders rarely occur together in Rocky Mountain National Park. Trout and tiger salamanders do coexist in some lakes (Dartt 1879; Blair 1951), especially where vegetated shallows provide habitat not easily accessible to the fishes. Levi and Levi (1955) surmised that trout may conflict with paedomorphic salamanders but not with metamorphosing populations.

Some have suggested that breeding-pond acidification related to atmospheric pollution may cause periodic failure of tiger salamander reproduction in the mountains of Colorado (Harte and Hoffman 1989, 1994). Low pH, even if not fatal to salamander larvae, may result in reduced growth rates and ultimately could diminish salamander populations through decreased survival or feeding success (Kiesecker 1996). However, recent water chemistry data, together with information on acid tolerances of salamander larvae, suggest that eggs and embryos in the wild do not experience harmful levels of acidification (Corn, Stoltzenburg, and Bury 1989; Corn and Vertucci 1992; Wissinger and Whiteman 1992; Vertucci and Corn 1994).

Under certain conditions, larval populations may be vulnerable to bacterial infections associated with livestock grazing. In the mountains of Utah, Worthylake and Hovingh (1989) observed recurrent mass mortality of larvae associated a bacterial infection and suggested that increased nitrogen levels due in part to sheep grazing may have been involved. Bryant (1995) observed a mass mortality event in the summer of 1993 that appeared to be associated with an opportunistically pathogenic bacterium. In Arizona, similar die-offs, apparently associated with bacterial pathogens, have been reported (Pfennig, Loeb, and Collins 1991). Cannibal morphs seemed particularly vulnerable, probably due to their feeding on diseased larvae. Again, fecal contamination of ponds by introduced livestock was suggested as a possible cause of the fatal outbreaks. In contrast to these reports, larvae sometimes do thrive in large numbers in manure-laden ponds in Colorado (Hammerson 1999). Nevertheless, die-offs of larvae, apparently associated with pathogenic bacteria, have been observed in Colorado (Hammerson 1999).

Infection by chytrid fungus, which has been associated with amphibian declines in several areas, has been observed in southern Arizona. Observations and experiments with salamanders and frogs indicated that chytridiomycosis does not always lead to mortality, individuals within a species vary in susceptibility to infection, animals appear to recover from the infection, and syntopic salamanders and frogs may act as reciprocal pathogen reservoirs for chytrid infections (Davidson et al. 2003).

Populations in the southeastern United States have been detrimentally affected by deforestation and loss of wetland habitats (Petranka 1998). Similarly, populations in the Great Plains have declined in the extensively cultivated portions of the Great Plains.

Local populations commonly incur massive mortality of adults on roads near breeding sites (Clevenger et al. 2001).

This species appears to be relatively stable in numbers. A. tigrinum is an adaptable species and can be found in many different habitat types so long as there is a suitable body of water for breeding and a terrestrial substrate that lends itself to burrowing (Hammerson et al. 2008).

Disease is a threat, with salamanders serving as both hosts and reservoirs of pathogens. Recent research has focused on transmission of Bd and ranaviruses (family Iridoviridae) via movement of Ambystoma tigrinum captured for the bait trade (Jancovich et al. 2005; Picco and Collins 2008). A. tigrinum appears to be a carrier of the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd), as it can be infected by Bd but does not appear to suffer mortality (Davidson et al. 2003).

The ranavirus ATV has been shown to be responsible for epizootics in tiger salamanders in the western cordillera of North America, from Canada (Saskatchewan and Manitoba) to North Dakota, Utah Colorado, and Arizona in the United States (Jancovich et al. 1997, 2005; for map see Storfer et al. 2007). In Canada, mass mortality events in both larval and adult A. tigrinum were observed in four separate ponds in Regina, southern Saskatchewan, in 1997; these die-offs were shown to be due to a highly infectious and virulent iridovirus (Bollinger et al. 1999). Concurrently a die-off at a more distant site 200 km north of Regina was also shown to be due to an iridovirus (Bollinger et al. 1999). In the United States,A. tigrinum die-offs were observed in Utah, Arizona, and Colorado populations, and these die-offs were initially thought to be due to bacterial infections (Worthylake and Hovingh 1989; Pfennig et al. 1991; Hammerson 1999). Arizona populations of A. tigrinum stebbinsi periodically suffered mass mortality events, beginning in 1985, which were also initially ascribed to bacterial infections (Collins et al. 1998). However, examination of dead and dying individuals from an Arizona die-off in 1995 found that a new, highly virulent iridovirus was the cause, and it was named ATV (for "Ambystoma tigrinum virus") (Jancovich et al. 1997). Phylogenetic analysis suggests that the ATV virus is endemic to Arizona populations of A. tigrinum, with strains of higher virulence present in commercially available bait shop larval salamander populations and then transferred into wild salamander populations as infected animals are moved and released (Storfer et al. 2007). Although larvae suffer the greatest mortality, metamorphosed individuals are also susceptible to infection, with juveniles and adults harboring sublethal infections for five months or more and thus capable of transmitting the virus to uninfected salamanders (Brunner et al. 2004; Collins et al. 2004). Exposure to pesticide can increase susceptibility to iridovirus infection in A. tigrinum larvae; the herbicide atrazine both significantly reduced the number of peripheral leukocytes and significantly increased infection rates (Forson and Storfer 2006; Kerby and Storfer 2009). Recent surveys of Arizona populations (Kaibab Plateau) of A. tigrinum found high prevalence of ATV (up to 57% of individuals were infected). The high prevalence of infection without corresponding disease symptoms suggests that either survivors may have evolved tolerance or the virus may have been reduced in virulence (Greer et al. 2009).

Threats other than disease include deforestation and habitat loss and fragmentation in wetland and other areas, as well as pollution of breeding habitat, introduction of predatory fish, and road mortality from vehicles. Habitat loss may cause local extirpations, particularly in eastern populations, which are patchily distributed, small in size, and variably declining (Zappalorti 1994; Semlitsch et al. 1996; Petranka 1998; Church 2003; Hammerson et al. 2008). Threats to aquatic habitat include draining and infilling of ponds and wetlands and water level reduction due to diversion for irrigation, and pollution from pesticides (BCRS 2008). Wetland desiccation, likely due to climate change, has led to decline of this species and other amphibians in Yellowstone National Park (McMenamin et al. 2008). Introduction of predatory fish can be an important cause of declines (see Blair 1951; Corn et al. 1997; Zeiber et al. 2008); trout and tiger salamanders generally do not co-exist unless there are well-vegetated shallows providing refuge from fish, and mosquitofish prey on tiger salamander larvae. Road mortality is a seasonal threat in localities where salamanders must cross busy roads to reach breeding habitat. Mortality may be moderate to severe (Richardson et al. 1998; Clevenger et al. 2001).

Although A. tigrinum is sometimes found in the international pet trade, current pet trade levels do not appear to pose a major threat (Hammerson et al. 2008).

In British Columbia, Canada, its range overlaps with at least two protected areas: South Okanagan Grasslands Provincial Park, White Lake Grasslands Provincial Park (BCRS 2008).

Preserve Selection and Design Considerations: Effective protection of breeding populations should include the aquatic fishless breeding site and a terrestrial buffer of at least a couple hundred meters.

Management Requirements: Needed measures include basic habitat protection and policies/regulations that discourage/prohibit the introduction of predatory fishes into habitats where they are not native.

Biological Research Needs: Further research on phylogeographic patterns and taxonomic status of major population segments is needed.

Global Protection: Very many (>40) occurrences appropriately protected and managed

Comments: Many occurrences currently are adequately managed, but long-term protection is not assurred. This species is protected under the category Pr (Special protection) by the Government of Mexico.

Needs: Needed measures include basic habitat protection and policies/regulations that discourage/prohibit the introduction of predatory fishes into habitats where they are not native.

The larvae are sometimes considered a nuisance in fish hatcheries. Large larvae will feed on very small fish, but their main effect might be to act as competitors with the fish. As the fish grow larger they can turn the tables and feed on the salamander larvae.

In some places Ambystoma tigrinum are captured and sold for fish bait (Harding 1997).

Comments: MtDNA data indicate that a vicariant event during the Pleistocene separated tiger salamanders to the east and west of the Apalachicola River (Church et al. 2003). East of the Applachians, there appear to be multiple Pleistocene refugia; populations along the Atlantic Coastal Plain likely were isolated in a coastal plain refugium in the Carolinas (Church et al. 2003). A second refugium may have been in the Blue Ridge Mountains in western Virginia; the now disjunct population in that area may be a relict of a warmer, more widespread fauna that is now restricted to the Coastal Plain (Church et al. 2003).

Comments: Ambystoma californiense formerly was regarded as a subspecies of A. tigrinum, but most evidence (morphology, allozymes, mtDNA) supports recognition as a distinct species (see Shaffer and McKnight 1996). See Kraus (1988), Shaffer et al. (1991), and Jones et al. (1993) for phylogenetic analyses of North American Ambystoma; californiense was treated as a full species in these analyses.

Pierce and Mitton (1980) reported substantial changes in allelic composition across a contact zone between subspecies mavortium and nebulosum in Colorado. Collins et al. (1980) speculated that A. tigrinum might actually be a multispecies conglomerate. Jones and Collins (1992) examined variation in polymorphic loci and found no obvious impediments to gene flow within a contact zone between these subspecies in west-central New Mexico.

A range-wide phylogenetic analysis of A. tigrinum and Mexican ambystomatids based on mtDNA data by Shaffer and McKnight (1996) revealed eight "reasonably" well-defined clades from the United States and Mexico; their data suggested that "species boundaries for several U.S. and Mexican species need to be altered and that the concept of a continentally distributed, polytypic tiger salamander is not valid." Irschick and Shaffer (1997) examined morphological variation in larvae of 60 populations of four subspecies of A. tigrinum, plus A. californiense and A. velasci, and tentatively concluded, despite relatively slight phenotypic differentiation among these populations, that subspecies tigrinum may be a valid taxon at the species level (separate from mavortium), though they acknowledged the problem of a broad zone of intergradation between subspecies tigrinum and mavortium, describing the classification of the intergrade populations as a "vexing and largely unresolved issue." Irschick and Shaffer also found that subspecies mavortium, nebulosum, and melanostictum are almost indistinguishable from one another on the basis on larval morphology. Subsequently, mavortium and tigrinum have not gained wide acceptance as distinct species. Petranka (1998), Hammerson (1999), and Crother et al. (2000, 2003) listed mavortium as a subspecies of A. tigrinum. Crother (2008) listed tigrinum and mavortium as distinct species but did not cite any new evidence supporting this and acknowledged that certain other recent publications regarded these taxa as conspecific.

There is good evidence that subspecies stebbinsi is the result of a past "hybridization" event between subspecies mavortium and nebulosum (see Jones et al. 1988, 1995).

See Fernandez and Collins (1988) for information on color pattern variation in subspecies nebulosum. See Kraus (1985) and Kraus et al. (1991) for information on the involvement of tigrinum in hybridization with other Ambystoma in Michigan. See Lowcock et al. (1987) for a discussion of the nomenclature treatment of hybrids.