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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Ambystoma Unisexual Salamanders
Ambystoma sp.
Family: Ambystomatidae
COSEWIC status:- Not at Risk (Blue-spotted Salamander population)
- Endangered (Jefferson Salamander dependent population)
- Endangered (Small-mouthed Salamander dependent population)
- No Status (Blue-spotted Salamander population)
- Endangered (Jefferson Salamander dependent population)
- Endangered (Small-mouthed Salamander dependent population)
- Not Assessed
Description
Ambystoma unisexual salamanders are heavy-bodied and can reach up to 20 cm in total length. The back and sides of adults are grey, brown or black, often with varying amounts of blue, grey or white flecks and spots that tend to be concentrated along the sides. The belly ranges from dark grey to black with blue flecks. Terrestrial juveniles have a light grey to brown background colour and smaller, more diffuse blue to yellow spots. Aquatic larvae are generally a mottled grey-brown with feathery gills behind the head, legs (both front and back) and a tail fin.
Similar Species
In many populations Ambystoma unisexual salamanders can be almost indistinguishable from Small-mouthed, Jefferson and Blue-spotted Salamanders, and genetic testing is required to confirm the identification. Ambystoma unisexuals often occur in higher densities than the other Ambystoma salamander species they depend on for successful reproduction (see Biology section). Aquatic larvae of the Ambystoma salamanders are difficult to distinguish from one another.
Distribution
In Canada, Ambystoma unisexual salamanders occur in southern and central Ontario, southern Quebec and as isolated populations in northern New Brunswick and central Nova Scotia. In the United States, the unisexuals have a spotty distribution throughout the Great Lakes region, including parts of Michigan, Ohio, Pennsylvania, Indiana, Illinois, New York, Vermont, New Hampshire, southern New England, New Jersey, Wisconsin, and Maine.
Habitat
Ambystoma unisexual salamanders are usually found in deciduous and mixed forests, typically within close proximity to breeding habitats. Leaf litter and cover objects, such as logs and rocks, are important microhabitats used for foraging and shelter. Individuals are sometimes found beneath wood piles and other debris in back yards. This species breeds in vernal pools (temporary woodland ponds) or fish-free permanent wetlands. These salamanders overwinter underground below the frost line in mammal burrows, root cavities and other underground crevices.
Biology
All individuals are female, with the exception of a small number of apparently sterile males. In Ontario, this salamander is only found in association with Small-mouthed, Jefferson or Blue-spotted Salamanders, from which they obtain sperm for reproduction. The Ambystoma unisexual salamanders migrate to breeding wetlands on rainy nights in early spring, often moving over snow banks and the icy edges of thawing ponds. Adults can migrate several hundred metres between overwintering and breeding sites. Each female will attach several clutches of approximately 30 eggs each as small gelatinous masses to submerged sticks or other vegetation. The eggs hatch into aquatic larvae after about one month, and the larvae transform into terrestrial juveniles by the end of summer. Individuals reach sexual maturity in three or four years and may only breed every few years. There is little information on the longevity of this species, but individuals may live more than 20 years based on studies on other Ambystomatid salamanders. After the breeding season, adults spend most of their time in underground burrows and cavities, making them difficult to find during the summer and fall. Adults and juveniles eat insects, spiders, worms and other terrestrial invertebrates, while larvae prey on immature aquatic insects and microcrustaceans. The taxonomic status for this salamander is not yet fully understood since they do not fit easily into current standards for species designation. In general, most species are diploid, containing two sets of chromosomes, one set inherited from each parent. Most Ambystoma Unisexuals are triploids, containing three sets of chromosomes, but higher ploidy levels can also occur.
Threats
The extensive conversion of natural habitat to agricultural and urban land uses has destroyed and fragmented much of this species’ habitat throughout the southern portion of its range in Canada, especially in Ontario. Ongoing habitat destruction, primarily from urbanization, cottage development and road construction, continues to cause population declines and local extirpation. Road mortality can be a significant threat to this species when roads bisect spring migration routes. Pollution, such as herbicides, agricultural effluent and road salt can be detrimental to salamanders since toxins are easily absorbed though their skin. Climate change and introduced pathogens pose potentially serious future threats to Canadian salamanders.