Amphiuma tridactylum
Three-toed Amphiuma

Amphiuma tridactylum is native to the south central United States. Their geographic range spans from south eastern Missouri to the eastern coast of Texas, through the gulf states to the shore of the Gulf of Mexico. They are also found in Arkansas and western Tennessee. Amphiuma tridactylum is most commonly associated with Mississippi River flood plains. ("Amphiuma Tridactylum", 2010; Dundee, 2004; Hammerson, 2004)

Three-toe amphiumas prefer swampy habitat and are often found in alluvial swamps, ditches, streams, lakes and calcareous swamps throughout their geographic range. They are sympatric with many species of crayfish and often seek shelter in abandoned crayfish burrows. These salamanders can live in ditches and temporary pools and are sometimes found in ditches of more developed urban areas. They are most often found in the murky waters of swamps and marshes. ("Amphiuma Tridactylum", 2010; Cochran and Goin, 1970; Dundee, 2004)

Amphiuma tridactylum is among the largest salamanders recorded. It has long cylindrically shaped body with four vestigial legs, and feet containing three toes. The hind legs are shorter than the front legs. The dorsum is dark brown to black in coloration and the venter tends is significantly lighter in comparison. The underside of the neck tends to be dark in coloration. Males are heavier than females of equivalent body length and often have wider, heavier heads than females. Adults have a maximum body length of 117 cm. Hatchlings range from 4.3 to 6.4 cm and newly metamorphosed individuals range in size from 6.1 cm. In general, Amphiuma species have two rows of teeth on their upper jaw; one which is located on the vomeropallatine, the other on the premaxillary. Amphiuma have teeth on their mandible as well. Amphiuma tridactylum is peadimorphic. It maintains gill arches and a laterally compressed tail throughout adulthood and also possess a lateral line system throughout its life as well. It also has lungs, and reduced, lidless eyes. Presumably as a form of defense, it secretes copious amounts of mucus, which makes it difficult to grasp ahold of. (Cagle, 1948; Dundee, 2004; Fontenot and Seigel, 2008; Glorioso, et al., 2010; Pough, et al., 2008; Thomas, 1996)

Amphiuma tridactylum metamorphoses in to adulthood but is paedimorphic and maintains larval features such as a laterally flattened tail and vestigial gill arches throughout its life. Most individuals are reproductively mature by 3 to 4 years of age, and females are considered sexually mature when they are 27 to 33 cm in length from snout to vent. There is no information available regarding sexual determination during development. (Cagle, 1948; Fontenot Jr., 1999)

Amphiuma tridactylum is polygynandrous, and mating occurs between January and April. Males court females by rubbing their snout on the female’s body. If the female is receptive, she returns the gesture and coils under the male to make their cloaca touch. During aquatic courtship, males swim rapidly in a circle and flap their tails above the surface of the water and slap the water’s surface. Female respond by swimming below the male and making their claoca touch. Females compete for mates, however, there no evidence to suggest that males compete for mates as well. Eggs are internally fertilized, as males deposit a spermatophore into the female's cloaca. Heavy rain has been shown to stimulate mating in this species. (Cagle, 1948; Fontenot Jr., 1999)

As the breeding season approaches, the cloaca of Amphiuma tridactylum males becomes swollen. Spermatogenesis takes place between October and May, peaking from December to March, and vitellogenesis,yolk formation in the eggs, takes place from September to May. Females mate biennially, and males mate annually. Females retain sperm in the spermatheca for up to 7 months and exhibit delayed fertilization. Amphiuma tridactylum lays its eggs under logs, on fallen branches and most commonly in its burrow near the water’s edge. Eggs are laid in strands like pearls on a string, and are of a jelly like consistency. Most egg masses consist of 50 to 200 eggs. Upon dissection, once specimen was found to have 354 developing follicles in her coelom. Eggs are opaque and are 10 mm in diameter on average. Eggs are deposited from January to September and have and require of 4 to 5 months to develop. Habitat conditions are a major determinant in how often a female reproduces. Females reproduce more often in permanent wetlands with abundant resources than in vernal habitats with limited resources. (Cagle, 1948; Dundee, 2004; Fontenot Jr., 1999)

Amphioma tridactylum females tend to their nests, and during dry periods aestivate in their burrows while wrapped in their eggs. Females also defend their eggs but do not prevent them from floating away. There is no information available regarding paternal care in this species. (Cagle, 1948; Fontenot Jr., 1999)

There is no information available concerning the average lifespan of Amphiuma tridactylum in the wild. Average lifespan of captive individuals is between 13 and 19 years. A close relative of A. tridactylum, Amphiuma means, reached a maximum age of 27 years in captivity. (Oliver, 1964)

Amphiuma tridactylum is nocturnal, and although most activity occurs between dusk and dawn, this species is most active around midnight. Amphiuma tridactylum aestivates in subterranean burrows during the dry season in vernal wetlands. In some regions of its geographic range (e.g., Louisiana, Mississippi, and Alabama) it is sympatric with Amphiuma means. It is non-migratory and occupies a small home range, which encompasses the burrow site and expands during breeding season. Amphiuma tridactylum has been shown to travel nearly 400 m at any one time. In general, members of Amphiuma move via lateral undulations of the body both on land and in the water, and their vestigial limbs are useless while in terrestrial habitats. This species is often found covered in bite marks, regardless of sex or age. These markings are through to be the result of its foraging behavior and not a result of predation or competition for mates. (Cagle, 1948; Fontenot and Seigel, 2008; Glorioso, et al., 2010; Karlin and Means, 1994)

There is no information available regarding the average home range size of Amphiuma tridactylum. Although Amphiuma tridactylum is capable of moving on land, is often not found more than a few meters from the water’s edge. It is more active and motile after a heavy rain or in areas where the ground is saturated. It spends most of the day in its burrow and emerges at night to feed. It does not travel great distances to forage. (Cagle, 1948; Dundee, 2004)

In general, members of Amphiuma have reduced lidless eyes and must rely on olfaction and their lateral line system to detect prey and potential predators. One report suggests that Amphiuma tridactylum can emit a high pitched whine when preyed upon. Although solitary throughout most of the year, males and females attract potential mates via chemical cues and communicate their willingness to mate via physical contact. (Cagle, 1948; Dundee, 2004; Harper, 1935; Thomas, 1996)

Amphiuma tridactylum is a generalist carnivore. Although preferred prey consists of crayfish, it is also known to feed on insects, worms, snails, small fish, small reptiles, and other amphibians. Cannibalism has been observed on occasion. Amphiuma tridactylum is an ambush predators and remains in its burrow with only its head protruding. It may also stalk prey until it is within striking distance. When attacking prey, it bites and tears while turning and thrashing in a manner similar to the death roll performed by members of Crocodylidae. (Cagle, 1948; Dundee, 2004; Oliver, 1964)

Other than a few species of snake, Amphiuma tridactylum has few natural predators. Mud snakes, king snakes, and water moccasins are all known to prey on A. tridactylum. This species cryptic coloration, burrowing tendencies, and ability to secrete copious amounts of mucus likely help reduce risk of predation. (Cagle, 1948; Harper, 1935)

Amphiuma tridactylum is a major predator of crayfish and other small aquatic vertebrates and invertebrates throughout its geographic range. It also preys on various species of insect and their aquatic larvae, potentially helping control insect pest populations. They are the dominant prey item for mud snakes and are also preyed upon by other species of snake as well. There is no information available concerning parasites specific to this species. (Cagle, 1948; Cochran and Goin, 1970; Dundee, 2004; Harper, 1935; Oliver, 1964)

Amphiuma tridactylum is consumed by humans in some parts of its geographic range and is kept as a pet by amphibian enthusiast. Amphiuma tridactylum has the largest red blood cells of any animal is often used as the model organisms in various biomedical research efforts as a result. (Dundee, 2004; Garrison, 1949)

Other than its painful, non-venomous bite, there are no known adverse effects of Amphiuma tridactylum on humans. (Cagle, 1948; Dundee, 2004; Harper, 1935)

Although precise populations estimates are unknown, Amphiuma tridactylum is classified as a species of least concern on the IUCN's Red List of Threatened Species. Despite this, amphibian populations across the globe are in steady decline due to habitat destruction, novel diseases and pollution. Fortunately, A. tridactylum faces no major threats at present and does not require specific conservation and management strategies to ensure its longterm survival. ("Amphiuma Tridactylum", 2010)