The spotted salamander (Ambystoma maculatum), also known commonly as the yellow-spotted salamander, is a species of mole salamander in the family Ambystomatidae. The species is native to the eastern United States and Canada. It is the state amphibian of Ohio and South Carolina. The species ranges from Nova Scotia, to Lake Superior, to southern Georgia and Texas. Its embryos have been found to have symbiotic algae, Chlorococcum amblystomatis, living in and around them, the only known example of vertebrate cells hosting an endosymbiont microbe (unless mitochondria are considered).
Description
The spotted salamander is about 15–25 cm (5.9–9.8 in) long (tail included), with females generally being larger than males. It is stout, like most mole salamanders, and has a wide snout. The spotted salamander's main color is black, but can sometimes be a bluish-black, dark gray, dark green, or even dark brown. Two uneven rows of yellowish-orange spots run from the top of the head (near the eyes) to the tip of the tail (dorso-lateral ranging). The spotted salamander's spots near the top of its head are more orange, while the spots on the rest of its body are more yellow. The underside of the spotted salamander is slate gray and pink. Sexual dimorphism (physical differences between males and females) is displayed in the form of larger-bodied females having brighter-coloured spots. Males will have a larger portion of the dorsal surface covered in spots that are less bright. There is also a correlation between body condition and spots having lower chroma. The scientific name Ambystoma maculatum comes from Ambystoma – amblys (Greek) for blunt; -stoma (Greek) meaning mouth; or anabystoma (New Latin) meaning "to cram into the mouth"; maculatum – macula (Latin) for spot; maculosus (Latin) for spotted. A. maculatum develops a larger tail fin and body to compete with other predators. It typically lives around 20 years, but some have lived up to 30 years.
Habitat and dispersal The spotted salamander usually lives in mature forests with ponds or ephemeral vernal pools for breeding sites. Vernal pools are suitable breeding sites for these amphibians as they dry often enough to exclude fish that eat the salamander eggs and larvae, while retaining water long enough to allow amphibian larvae to complete development and metamorphose into terrestrial adults. A study showed larger pools (as opposed to smaller pools) had more egg masses, higher occupancy, and higher larval survival rates for spotted salamanders. Outside of the breeding season, these salamanders spend their time in forests with well-drained soils that contain many burrows dug by small mammals. They have also been known to be absent from landscapes and forest with canopy cover below 30%. Juveniles are the main source of population dispersion. They prefer forest over successional forest over fields. They can detect forest from 10 m away. Early successional forest could be an ecological trap. Salamander populations from nearby pools form genetically-distinct metapopulations. Subpopulations within 4.8 kilometers share a higher proportion of genes, while populations greater than 4.8 kilometers share a smaller proportion of genes. Inter-population dispersal is likely mediated by both species-specific behaviors and natural limitations. Spotted salamanders have significant variation in length and body mass both within and between populations. Variation within a population is typically greater than variation between populations leading to the theory that variation is due to microhabitat and level of heterogeneity rather than genetic distinction.
Behavior The spotted salamander is fossorial. It rarely comes above ground, except after a rain or for foraging and breeding. During the winter, it brumates underground, and is not seen again until breeding season in early March–May. In North Amherst, Massachusetts, United States, spotted salamanders cross the street to get from their overwintering sites in the wooded area east of the roadway to their breeding sites to the west. Local officials built amphibian and reptile tunnels called the Henry Street salamander tunnels to help the salamanders cross the road to get to vernal pools. In the spring after rain and when temperatures rise above 40 °F (4 °C), salamanders emerge from underground. They cross Henry Street to get to their breeding grounds, vernal pools which form on the other side of the road, an event common among amphibians and known as the Big Night. A. maculatum has several methods of defense, including hiding in burrows or leaf litter, autotomy of the tail, and a toxic milky liquid it excretes when perturbed. This secretion comes from large poison glands around the back and neck. The spotted salamander, like other salamanders, shows great regenerative abilities: if a predator manages to dismember a part of a leg, tail, or even parts of the brain, head, or organs, the salamander can grow back a new one, although this takes a massive amount of energy. As juveniles, they spend most of their time under the leaf litter near the bottom of the pools where their eggs were laid. The larvae tend to occupy refuges in vegetation, and lower their activity in the presence of predators. A. maculatum tend to follow the same path in their migration to and from their burrows and breeding pools. They accomplish their journey in conditions that lack visual cues, since it is usually during periods of cloud cover. Some studies show evidence of landmark learning and use of geotaxis in spotted salamanders. Researchers found that spotted salamanders can associate visual landmarks with food. Thus spotted salamanders may learn landmarks in their habitat that are reliable indicators of resource locations or provide orientation clues for migration to and from breeding ponds. Male salamanders come out earlier than females due to different responses in temperature than females. According to a study there is a correlation between the salamander's spot coloration and body condition. Salamanders in lower body condition had less color and those with a better body score had brighter colored spots.
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