The marbled salamander, Ambystoma opacum, is a fascinating amphibian species endemic to North America. Known for its distinctive markings and unique breeding habits, this member of the mole salamander family plays an important role in its ecosystem. This article delves into the marbled salamander's habitat, diet, and life cycle, highlighting its ecological significance and conservation needs.
Identifying Characteristics and Size
The marbled salamander is a short and stocky salamander, with adults typically reaching lengths of 3 1/2 to 5 inches (approximately 9 to 12.7 cm). As with many Ambystomatids, the marbled salamander is a relatively stocky species. They have smooth, dark gray to black skin, or even deep purple above with a gray belly. Light silver to white markings are on their back. They have a stocky body with a short, broad head, and a relatively short tail for a salamander - their tail is 40% of their total length.
One of the most distinguishing features of the marbled salamander is the presence of white or gray crossbands on a dull black body, often forming a “marble” pattern. Band width varies, and bands may merge, form circles on the back, or have gaps. The male has white bands and the female has gray bands. Males are typically smaller than females and, during the breeding season, their silvery-white crossbands become bright white. The larger females have bands that tend to be more silvery-gray than white, although these markings can vary dramatically between individuals. Bands generally do not reach the black underside.
Recently metamorphosed marbled salamanders are gray or brown with pale speckles and have striped toes. The larvae are typically black or dark brown with light spots along the side. Juveniles have white flecks that eventually develop into bands as they reach adulthood.
Marbled salamanders exhibit sexual dimorphism, with males having white dorsal bands and females having silver dorsal bands. Males also have a larger proportion of white dorsal surface area relative to females. Females have been reported to have more asymmetrical dorsal markings, while the males have more symmetrical markings. The coloration and size of the females is considered adaptations for reproductive success and nest brooding. The darker coloration allows them to thermoregulate easier, and the larger size allows them to produce more and larger eggs. These adaptations are not necessary in males.
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Distribution and Habitat
The marbled salamander can be found from southern New Hampshire to northern Florida, and west to southern Illinois, southeast Oklahoma, and east Texas. It is also found around Lake Erie and Lake Michigan and in south west Missouri and along the northern border of Ohio and Indiana. This species is a relatively common resident throughout North Carolina and Alabama, though it is rarely seen because of its nocturnal habits.
Marbled salamanders live in forests and woodlands. Found throughout the entire state, marbled salamanders occur in habitats ranging from moist woodlands to dry, wooded hillsides, but never far from a moist environment. Flood plains and low hammocks are their preferred habitats. They can be found in a variety of habitats, from moist sandy areas to dry hillsides, and they are best found by looking under debris such as logs or rocks. They prefer to reside in damp woodlands that are close to floodplain pools and ponds. They are occasionally spotted on dry hillsides, but rarely stray far from moist environs. Overall, they are more tolerant of dry habitat than many other salamanders, due to their burrowing ability. Riparian areas (land adjacent to water) or swampy areas with slow moving water are the marbled salamander's preferred habitat.
Like the mole, which gives rise to the common name of this family of salamanders, marbled salamanders create burrows and tunnels and spend most of their time underground. The adults are nocturnal, spending the days under logs and leaf litter or in burrows. They spend most of their time in a burrow, in leaf litter or under bark and logs. Marbled salamanders are more tolerant of dry habitats because they create burrows under logs, leaf litter, or underground, a behavior that is uncommon in other salamander species.
Diet and Feeding Habits
Marbled salamanders are effective predators, consuming large amounts of food. Adult marbled salamanders eat invertebrates including earthworms, insects, crickets, ants, snails, slugs, spiders, and centipedes. Marbled salamanders only eat live prey.
The larvae of the marbled salamander are also quite voracious predators. Larvae eat zooplankton. As they grow, they will eat tadpoles, insects and other salamander larvae. As they grow larger, they will eat aquatic insects, isopods, fairy shrimp, snails, worms, and the larvae of other amphibians. The larger larvae will also eat caterpillars and other terrestrial invertebrates that fall into ponds.
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Reproduction and Life Cycle
Marbled salamanders are late summer to early fall breeders. Notably different from salamanders in the same family, the marbled salamander breeds on land in the fall, rather than in water during spring. Breeding in Alabama occurs during October and November. Both males and females typically migrate to the area surrounding a dry vernal pool in September and October. As summer ends and autumn rains begin, Marbled Salamanders migrate from upland habitats down to those dried vernal pools.
Unlike other members of the Family Ambystomatidae, the marbled salamander does not breed in the water. Adults gather in depressions on the forest floor beneath logs, leaf litter or other debris where they engage in courtship and mating. Courtship of this species takes place on land. The males will compete by butting heads and blocking another male's movement with its tail. When courting the female, a male will nudge the vent of a female with its snout, with the intent that the female will respond in kind. This back-and-forth nudging has the appearance of a dance as the two salamanders circle around one another. There is no association between mating success and size of salamander, it depends only on this display. Males court females and produce spermatophores from which the females obtain sperm. Males will deposit sperm packets called spermatophores on the ground. Interested females will pick up the spermatophores with their cloacal lips and inseminate their eggs.
The female constructs a nest under moss, leaves or cover objects in a dry area of the pool basin and deposits 50-200 small transparent eggs, one at a time, in a depression under a log or in a clump of vegetation that will fill with water when it rains. The female lays 50 to 200 individual eggs, often remaining with them until the nest floods. Females will lay 50 to 200 individual eggs in protected areas within the depressions. The female usually curls her body around the eggs to keep them moist and waits for rain to fill the depression. Females usually curl themselves around the eggs to keep them moist and guard them until rains flood the nest sites. One fairly unique parental care behavioral characteristic of Marbled Salamanders is that when the mothers stay with their eggs, wrapping their bodies around the eggs to form a bowl shape to collect water over the eggs. Water must make extended contact with the eggs in order for them to begin hatching. The females lay eggs in a dried up depression, pool or pond then guard them until the depression fills with water. Nest site selection can be important to reproductive success. The females select a point between the shallowest and deepest area of the ponds. Then they lay their eggs one at a time in a shallow depression under vegetation, encircling the eggs until the depression fills with water from spring rains. This behavior is called brooding the eggs.
Larvae develop within the egg and hatch when the eggs are flooded in the fall. If the eggs are covered with water in the fall, they will develop and hatch before winter. The larvae hatch a few days after being covered by water. If there is not enough autumn and winter rain, the larvae may not hatch until spring! Newborn salamanders, called larvae, will feed on a variety of prey after hatching, starting with zooplankton and diversifying to worms, larvae, aquatic insects and isopods as they mature. Larvae eat zooplankton, small invertebrates, and other salamander larvae.
Marbled salamander larvae are carnivorous and feed throughout the winter, under the ice, on zooplankton and available small invertebrates. As they grow, they feed on larger prey, eventually consuming most anything they can get in their mouths. By spring, they are able to feed on the hatching larvae of wood frogs and other species of mole salamander.
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The larvae transform into the land-dwelling form in May and June. Upon metamorphosis, they have a grayish-blue spotted pattern on a purplish-black body. Young are generally brown to black with light spots or mottling dorsally (on top) and laterally (on sides). Marbled salamanders darken as they mature.
Their lifespan is about four years.
Threats and Conservation
Marbled salamanders exhibit strong fidelity to their breeding ponds. The primary threats facing marbled salamanders in New Jersey are the loss, alteration, and degradation of quality habitat. Specialized habitat requirements and strong fidelity to breeding ponds render these salamanders vulnerable to habitat loss. In addition, restricted range and isolated populations hinder their ability to recover from localized extirpations or declines. They have suffered from degraded water quality in these ponds.
An expanding network of roads fragmenting forests may impede salamander movements to breeding ponds or result in road mortality of migrating adults and dispersing juveniles. Unfortunately, roads often transect the upland habitats and vernal pools that Marbled Salamanders have to migrate to and from. A road is no place for most animals, and thousands of Marbled Salamanders are killed by vehicles every year. Luckily, several organizations (Heritage Conservancy included) have made efforts to assist this species in its dangerous treks across roads. Salamander crossings, made possible by volunteers, have helped hundreds of Marbled Salamanders off the road so they can successfully breed and make it back to their overwintering grounds.
Worldwide, many amphibian populations are declining or have disappeared completely. There are many possible causes for this decline - acid rain, herbicides, insecticides, fertilizers, industrial waste, habitat destruction, introduced species, bacteria, ozone depletion, and global warming. It could be a combination of any or several of these suspected causes, however much study is needed to solve the mystery, saving marbled salamanders and other amphibians.
Marbled salamander locales, including breeding ponds and terrestrial habitats, should be protected from development, habitat degradation, and the reduction of water quality. The continued success and diversity of salamanders in North Carolina depends on public advocacy and action to conserve ephemeral pool habitats and their adjacent upland forests.
Defensive Mechanisms
When A. opacum is under attack by a predator, they often exhibit tail lashing, head-butting, body coiling, or potentially becoming immobile. These defensive moves are thought to draw attention to the tail, which has granular glands that produce noxious secretions to protect themselves. While some predators have learned to eat the body of Marbled Salamanders and leave the tail, this is still a deterrent for many predators.
Conservation Status and Regulations
The marbled salamander is classified as a nongame species with no open season.
Marbled Salamanders as State Symbols
The marbled salamander is North Carolina’s State Salamander, thanks, in part, to efforts by the N.C. Herpetological Society, which helped lead the effort to designate state amphibians. The designation became official on June 26, 2013.
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