Tiger salamander (Ambystoma tigrinum)
|Size||Length: up to 35 cm (2) (3)|
- The tiger salamander is the largest and most widespread terrestrial salamander in North America.
- The tiger salamander is named for its yellow, tiger-like spots and streaks.
- Occasionally, tiger salamander larvae develop into a ‘cannibal’ morph which has a larger head and longer teeth, enabling it to feast on other larvae.
- Some adult tiger salamanders do not undergo metamorphosis into a terrestrial form, instead remaining aquatic and retaining their gills.
The tiger salamander is classified as Least Concern (LC) on the IUCN Red List (1).
The largest terrestrial salamander in North America (4), the tiger salamander (Ambystoma tigrinum) is a brightly coloured amphibian named for its yellowish, tiger-like patterning. This large, stout-bodied salamander has well-developed limbs, a large head, a broad, rounded snout and relatively small eyes (3) (5) (6) (7) (8). The tiger salamander’s tail is long, flattened from side to side, and has a ridge along the top (8).
The tiger salamander’s large, irregular, yellow to yellow-brown spots and streaks contrast with its otherwise dark brown to grey or black body. The underside of the body may be marked with patches of pale yellow, usually on a darker or greyish background, or may be yellowish with dark mottling (3) (5) (6) (7).
Male tiger salamanders can be distinguished from the females by their longer, more flattened tails and longer hind legs, and also have a swollen vent during the breeding season (3) (6) (8). In addition, the male tiger salamander is generally slightly smaller than the female (2) (3).
The aquatic larvae of the tiger salamander are usually olive-green or yellowish-green (5) (6) with darker blotches along the back and a whitish belly (6). There is also usually a light stripe along each side of the body (3) (6). The larvae have large, rounded heads and long, feathery gills (3) (5) (6) (7) (8).
Occasionally, perhaps in response to overcrowding, some tiger salamander larvae develop into a ‘cannibal’ morph. This morph has a larger head, more flattened snout and larger teeth, enabling it to feast on other salamander larvae, including those of its own species (2) (3) (6) (7) (9).
Newly metamorphosed tiger salamanders are greyish to brown, with lighter mottling, and gradually gain their yellow patterning over a few weeks (6). In some tiger salamander populations, individuals do not transform into the terrestrial adult form and instead remain aquatic, retaining their gills. However, these ‘neotenic’ individuals are still able to reproduce (2) (3) (4) (6) (7), and if the pond dries up they may be able to undergo metamorphosis and become terrestrial (2).
Around six to seven subspecies of the tiger salamander are generally recognised (2) (3) (7), although the status of some of these has been debated (2) (3). The tiger salamander can be distinguished from the similar-looking spotted salamander (Ambystoma maculatum) by its irregular yellow spots, streaks and blotches rather than regular rows of yellow spots (6) (8).
The tiger salamander is the most widespread salamander species in North America (2) (5), occurring from southern Canada, through the United States to northern Mexico. Although it occurs throughout much of the United States, this species is absent from the Great Basin, New England and the Appalachian Mountains (1) (5) (7). However, it has been introduced into some areas outside of its natural range, such as in central California (1) (5).
The tiger salamander is found in a wide range of habitats, from woodlands to more open areas such as grassland, marshes, fields and even deserts (2) (5) (6) (8). However, it generally requires areas with soil that is suitable for burrowing and with a nearby water body for breeding (1) (6) (7) (8).
This species has been recorded at elevations of up to 3,660 metres (1) (5).
Adult tiger salamanders are usually terrestrial and spend most of their lives underground, either in a burrow they have dug themselves or in the burrow of another animal (1) (2) (3) (5) (6) (8). Individuals of this species have been found up to two metres below the soil surface (2). Members of the family to which the tiger salamander belongs, the Ambystomatidae, are commonly known as ‘mole salamanders’ due to this predominantly underground existence (3) (4).
On rainy nights between late winter and early spring, the adult tiger salamander migrates from its burrow to its breeding ponds (2) (5) (6) (7) (8). These ponds normally lack fish, which may prey on the salamander’s eggs and larvae, and range from clear mountain pools to temporary lowland ponds, farm ponds, gravel pits, ditches and ornamental ponds (1) (2) (5) (6) (7).
Male tiger salamanders typically arrive at the breeding grounds a few days before the females (2) (3) (6) (7). Courtship takes place at night and involves the male nudging the female with his snout, possibly to move her away from other males, before leading her forward. The male then deposits a package of sperm known as a spermatophore, which the female picks up in her cloaca (6).
The female tiger salamander lays rows or clusters of eggs on submerged vegetation or on the bottom of the pond (2) (5) (6) (7). Each egg mass contains up to 100 or so eggs (3) (6) (8), and each female may potentially produce several thousand eggs in a breeding season (2) (7). The tiger salamander’s eggs hatch in about two to six weeks, depending on the water temperature (6) (7) (8).
The larvae of this species measure around 1.3 to 1.7 centimetres in length on hatching (6), but grow rapidly, sometimes reaching 10 to 15 centimetres in length before they metamorphose (2) (3) (6) (7). Tiger salamander larvae can undergo metamorphosis at around ten weeks old (2), but many take much longer, sometimes even overwintering in the pond and transforming the following spring (2) (6). After metamorphosis, the newly transformed adult salamanders usually migrate away from the water (2). The tiger salamander may be able to breed at a year old (3) (6) (7).
Adult tiger salamanders feed on a variety of insects, worms, snails, slugs, and even small vertebrates, such as mice, frogs and lizards. The larvae of the tiger salamander eat any prey which can fit into their mouths, including small crustaceans, insect larvae, molluscs, leeches, frog tadpoles, other salamander larvae, and even small fish (2) (3) (6) (7) (8). ‘Neotenic’ adults, which remain aquatic, have a similar diet to the larvae (2).
The tiger salamander’s eggs and larvae are vulnerable to a wide range of predators, including aquatic insects, newts, larger salamander larvae, birds, snakes and fish, and only a small number reach adulthood. Adult tiger salamanders may be taken by snakes, birds and mammals (2) (6) (7) (8), but those that survive can potentially be quite long-lived (5) (6), with individuals in captivity reaching over 20 years old or more (2) (5) (6). To deter potential predators, the adult tiger salamander produces noxious secretions from glands on the upper surface of its tail, and may raise and lash its tail if threatened (2) (6) (8).
As it is a widespread and adaptable species which is able to occupy a range of habitats, the tiger salamander is not currently believed to be at risk of extinction. It is one of the most abundant Ambystoma species, and in some areas it has benefitted from the creation of small, artificial water bodies lacking fish (1) (6).
However, despite being locally common, the tiger salamander faces a number of threats. Some populations are small and patchily distributed, and may be in decline (1), while others have been lost entirely (1) (2). One of the main threats to the tiger salamander is the introduction of fish to its breeding ponds, as the fish prey on its eggs and tadpoles. Deforestation and the loss of wetlands are a problem in some areas (1) (2) (3) (5) (6), and many adult tiger salamanders are killed crossing roads while migrating to and from their breeding pools (5) (6) (8).
Other potential threats to the tiger salamander include disease (1) (5) and the acidification of its breeding ponds, which could affect its reproductive success (1) (2) (7). This colourful amphibian is sometimes seen in the international pet trade, although not at significant levels (1) (2). However, the larvae of the tiger salamander, sometimes referred to as ‘waterdogs’, are commonly caught and sold as fish bait. As a result, thousands of larvae have been moved to different parts of the United States, resulting in the introduction of the tiger salamander to new areas (2) (7) (10). Where this occurs, it has sometimes resulted in the tiger salamander hybridising with native species such as the California tiger salamander (Ambystoma californiense) (2) (10), and it may also exacerbate the spread of disease (10).
There are no specific conservation measures currently known to be in place for the tiger salamander, but its range does include some protected areas (5) and the species is legally protected in Mexico (1). Recommended actions for this large amphibian include increased protection of its habitat, including regulations which discourage the introduction of predatory fish into its breeding ponds (1). The building of ‘walkways’ beneath busy roads may help protect tiger salamanders as they move to and from their breeding pools (8).
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- Cloaca: a common cavity into which the reproductive, digestive and urinary systems open in birds, reptiles, amphibians, most fish and some primitive mammals.
- Crustaceans: diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
- Gland (glands): an organ that makes and secretes substances used by the body.
- Hybridisation (hybridising): cross-breeding between two different species or subspecies.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Metamorphosis (metamorphose, metamorphosed): an abrupt physical change from the larval to the adult form.
- Molluscs: a diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
- Morph: one of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).
- Spermatophore: a capsule or mass of sperm transferred from a male to a female during mating, for example in certain insects, arthropods and cephalopods (octopuses and squids).
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Vertebrates: animals with a backbone, including mammals, birds, reptiles, amphibians and fish.
IUCN Red List (August, 2013)
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AmphibiaWeb - Ambystoma tigrinum (August, 2013)
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