Top carnivore

Tiger Salamander

The Tiger Salamander (Ambystoma tigrinum) is a species of Mole Salamander. The proper common name is the Eastern Tiger Salamander, as to differentiate from other closely related species.

Description

Eastern tiger salamanders are large, with a typical length of 6-8 inches. They can reach up to 13 inches in length, particularly neotenic individuals. Adults are usually blotched with grey, green, or black, and have large, lidded eyes. They have short snouts, thick necks, sturdy legs, and long tails. Their diet consists largely of small insects and worms, though it is not rare for an adult to consume small frogs and baby mice.

Adults are rarely seen in the open and often live in burrows. Tiger salamanders are almost entirely terrestrial as adults, and usually only return to the water to breed. Like all ambystomatids, they are extremely loyal to their birthplace, and will travel distances to reach it. However, a single tiger salamander has only a 50% chance of breeding more than once in its lifetime. Males nudge a willing female to initiate mating, and then deposit a spermatophore on the lake bottom. The female picks up the packet and deposits the now-fertilized eggs on vegetation. Large-scale captive breeding of Tiger salamanders has not been accomplished, for unknown reasons.

The larvae are entirely aquatic, and are characterized by large external gills and a prominent caudal fin that originates just behind the head. Limbs are fully developed within a short time of hatching. Larvae come in two types - cannibalistic and non-cannibalistic. High larvae density is said to trigger the cannibalistic phenotype, which has a much larger head than normal. Some larvae, especially in seasonal pools and in the north, may metamorphose as soon as feasible. These are known as small morph adults. Other larvae, especially in ancestral pools and warmer climates, may not metamorphose until fully adult size. These large larvae are usually known as waterdogs, and are used extensively in the fishing bait and pet trade. Some populations may not metamorphose at all, and become sexually mature while in their larval form. These are the neotenes, and are particularly common where terrestrial conditions are bad.

Conservation status

While remaining locally common in many regions, Tiger Salamander numbers have declined compared with historical levels. One of the largest threats to Tiger Salamander populations is wetland destruction and alteration through aquaculture activities. Since they tend to breed in semipermanent wetlands, larval Tiger Salamanders often experience mass mortality in association with pond drying. Introduced fishes have also been known to reduce, and sometimes eliminate, populations since Tiger Salamanders generally require a habitat where they are the top carnivore. Deforestation is also a problem, although most prevalent in Southeastern and Midwestern populations. Northeast populations tend to be most affected by acid deposition. Adult Tiger Salamanders avoid waters with a low pH. At a pH of 4.2, 50% of embryos suffer mortality. In addition, at these low pH levels they also experience reduced growth and longer larval periods. The effect of agricultural pesticides in endocrine disruption has also been researched. All of these issues have collectively influenced Tiger Salamander populations. However, Tiger Salamanders are only listed as endangered in Delaware, New York, New Jersey and Maryland; protected in Arizona; and of special concern in both North and South Carolina. (http://www.amphibiaweb.org) In November 2001, the Canadian Species at Risk Act listed the Great Lakes population of the Tiger Salamander as being extirpated, and the Southern Mountain population in British Columbia's Okanagan as endangered in Canada.

Tiger salamander adults are also often sold as pets, or used in research. Nearly all such salamanders are wild-caught.

Relative species

The California Tiger Salamander (Ambystoma californiense), the Barred Tiger Salamander (Ambystoma mavortium), and the Mexican Tiger Salamander (Ambystoma velasci), were all once subspecies of A. tigrinum, but are now considered separate species. Genetic studies made it necessary to break up the original A. tigrinum population, even though there is some hybridization between groups.

Trivia

In 2005, Illinois voters chose the Eastern Tiger Salamander as their State Amphibian.

References

External links

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