Amphiuma pholeter

Geographic Range

One-toed amphiumas ( Amphiuma pholeter ) are a native Nearctic species with a narrow range of about 80-120 km inland from the eastern Gulf Coastal Plain of the southeastern United States. Their range extends as far west as southern Mississippi extending continuously along the coast to central Florida, just north of Tampa, and occurring between the Gulf Hammock region and the Yellow River south of Crestview city in the Florida peninsula and panhandle. Their range extends northward in southwest Georgia into Thomas and Brooks counties and the Ochlockonee River drainage. They extend 50 km north into southern Alabama in the steep headwaters in Covington County.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Adult and juvenile one-toed amphiumas inhabit lakes, ponds, wetlands, and swampy floodplains associated with small, permanent, or near permanent streams that have a low to moderate gradient flow. They are prevalent in mixed bottomland hardwoods and cypress ( Taxodium ) environments with deep organic “muck beds”. These muck beds are defined by their composition - mostly hardwood leaf litter and cypress needles, with an organic layer that provides camouflage. One-toed amphiumas are commonly found in deep, organic liquid muck deposits of 30-60 cm deep as they cannot maneuver through fibrous peat. These animals are rarely found in shallow muck less than 15 cm deep. They typically inhabit low-elevation regions primarily 0m above sea level. Amphiumas can create their burrows in peat and can also be found under muck-buried logs. Unlike some amphibians, amphiumas do not undergo long-distance migrations but, they may move short distances in response to seasonal flooding and drying.

Minimum elevation is sea level, or 0 m. Upper limits of elevation are not reported.

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Terrestrial Biomes
• forest forest

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools

• Wetlands
• swamp swamp

Physical Description

Adult one-toed amphiumas are an elongated slender, eel-like amphibians typically ranging from 20 to 33cm in length. Means and Gunzburger Aresco (2020) reported amphiumas from Florida averaged snout-vent lengths of 175 mm (range 98-247mm) in males and 171 mm (range 95-234mm) for females. Tail lengths were typically 48-50mm, but ranged from 27-67mm. The reported average weight from Means and Gunzburger Aresco (2020) for females was 14g (range 8-20g) while males reported an average weight of 13g (range 7-18g). Given this substantial overlap between sexes, there is no apparent sexual dimorphism. One-toed amphiumas possess four small limbs, each with a single toe, reduced eyes, and a pair of gill slits. The tail is slightly flattened laterally, and the head is conical with a rounded snout. They are uniform in color, appearing dark brown to gray with a slightly lighter ventral underside, giving it a “dusky” appearance.

Larvae of amphiuma species are largely unstudied but smaller amphiumas that have been sampled (total length < 10 cm) resemble adults in body shape. They are black with a light gray ventral coloration. Hatchlings possess external white gills that are shed shortly after hatching.

One-toed amphiumas are unique because they are the smallest of the Amphiuma species reaching a maximum length of about 33 cm. Two-toed amphiumas ( Amphiuma means ) are the largest salamanders in North American and reach up to 114 cm while three-toed amphiumas ( Amphiuma tridactylum ) grow to about a total length of 104 cm. They also are differentiated by the number of toes, as the common names suggest.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

The growth and development of one-toed amphiumas remains largely unknown and poorly understood due to their burrowing lifestyle. Like most amphibians, amphiumas exhibit indeterminate growth, continuing to grow throughout their lives. Female one-toed amphiumas have been found with eggs in them, but the gestation and incubation periods are unknown. The incubation period for other amphiumas in the genus is 5-6 months. Larvae have not yet been observed in the wild, so it is uncertain whether they develop fully in the egg before hatching or experience a free swimming larval stage. Lannoo (2005) suggests that newly hatched larvae may have delicate, feathery gills and undergo a brief larval stage before developing into air-breathing juveniles. This assumption is supported by studies of three-toed amphiumas ( Amphiuma tridactylum ), whose larva hatch with gills and reabsorb them within two weeks. Small juvenile one-toed amphiumas held in captivity took at least 2 years to attain adult size. One-toed amphiumas exhibit obligate neoteony, meaning that they continue to exhibit some larval traits into maturity.

• Development - Life Cycle
• neotenic/paedomorphic
• metamorphosis metamorphosis
• indeterminate growth indeterminate growth

Reproduction

Courtship and mating behaviors for one-toed amphiumas remain largely unstudied, but limited information is available for other members of the species, two-toed amphiumas ( Amphiuma means ) and three-toed amphiumas ( Amphiuma tridactylum ). Like other salamanders, amphiumas likely use chemical, visual, and tactile signals in courtship. All three species are known to engage in biting during mating rituals. Studies suggest that courtship occurs in water and internal fertilization has been confirmed for three-toed amphiumas. Courtship of others in the genus have been observed to take place in winter and spring while egg laying occurs in late spring and summer.

Not much is known about gestation or incubation period of one-toed amphiumas. Female amphiumas will lay eggs in moist terrestrial environments. Observations of two-toed amphiuma ( Amphiuma means ) nests suggest that they are typically found in damp areas near bodies of water or within drying pond basins. During the winter and spring, females will deposit long strings of 20-200 eggs under logs, rocks, roots, or other natural debris. The incubation period for other amphiumas in the genus is 5-6 months. It is assumed that internal fertilization takes place underwater. One-toed amphiumas are a gonochoric species, meaning each individual is either male or female. Like all amphibians, they are iteroparous, meaning they reproduce more than once in their lives.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Due to their burrowing lifestyle, parental care has not been observed for one-toed amphiumas. Two-toed amphiuma ( Amphiuma means ) nests have been found with the female attending to the eggs. The female amphiumas do not flee when nests are uncovered, suggesting that they are the ones to defend the eggs. It is assumed that similar to two-toed amphiumas, one-toed amphiuma females will coil around eggs to provide protection until they hatch. Gravid female amphiumas have been found co-occuring with other adult and juveniles. One-toed amphiuma nests or hatchlings have not been found, but it is assumed that males provide no paternal investment beyond the act of mating.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Lifespan for one-toed amphiumas in the wild is unknown and unreported for all members of the genus. One anecdotal report state that one-toed amphiumas raised entirely in captivity lived 5 years, but died “accidentally.” Therefore, it’s suggested that this is neither a maximum or expected lifespan in captivity; these animals could have survived for a long time block. Other species in the genus lived in captivity for 14 to 27 years in zoos.

Behavior

One-toed amphiumas are a motile species, meaning they arecapable of movement and travel through their environment. Amphiumas are fossorial, adapted for burrowing underground to create shelters or navigate their habitat. One-toed amphiumas are assumed to be natatorial or specialized for swimming, due to reproduction likely taking place underwater. Bite marks observed from male-male aggression suggest that male amphiumas are territorial and they defend small territories within their home range. They are also thought to be nocturnal.

Courtship and mating behavior in one-toed amphiumas remain largely unstudied. However, two-toed amphiuma ( Amphiuma means ) females are known to lay eggs in moist terrestrial environments, under logs, rocks, or natural debris.

Communication and perception in one-toed amphiumas rely largely on chemical, visual, and tactile cues. Chemical signals are used to identify conspecifics and recognize mates, and reproductive status. Like most salamanders, amphiumas detect signals through vomeronasal cues, using their tongue or sensory receptors. Because of their small lidless eyes, visual communication is limited. Amphiumas use tactile interactions like rubbing or nudging to aid in navigation and interspecies communication. From November to March, unearthed individuals are in a state suggesting brumation. Other individuals may migrate short distances to slightly warmer microhabitats like the root systems of wetland shrubs.

• Key Behaviors
• fossorial fossorial
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• hibernation hibernation
• territorial territorial

Home Range

Home range has not been reported for one-toed amphiumas. Two-toed amphiumas ( Amphiuma means ) maintain a small home range of about 12.4 m^2 and juveniles are presumed to have a smaller range than adults. Male amphiumas have been observed with bite-mark scars from male-male aggression, suggesting that they defend small territories within their home range.

Communication and Perception

One-toed amphiumas rely on chemical, visual, and tactile cues to communicate and perceive their environment. Like most salamanders, one-toed amphiumas depend primarily on chemicals, particularly for finding mates and courtship. They leave behind pheromone trails through excretion to distinguish between species and to identify the sex and reproductive status of other amphiumas. Most salamanders detect chemical signals through vomeronasal cues. They pick up odor chemicals with either their tongue or through sensory receptors on the surface of their heads and then are transported to nasal sacs. In addition to chemical communication, amphiumas use visual cues. One-toed amphiumas like other species of ampiumas are not dependent on sight; their small lidless eyes suggest that vision is limited and plays a secondary role in communication. This aligns with their nocturnal and burrowing lifestyle where vision is limited due to their habitat. Salamanders also engage in tactile behaviors such as nudging, rubbing, or butting their bodies against each other. These survival behaviors include burrowing, allowing them to navigate their environment, locating food, and communicating with potential mates. One-toed amphiumas perception is largely reliant on their ability to detect various sensory cues in their environment. Amphiumas also possess the lateral line system. This is visible as slits on the snout and pores on the body, which enable them to detect vibrations in the water.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

One-toed amphiumas of all age classes and both sexes feed year-round on a variety of small invertebrates. Their diet primarily includes aquatic crustaceans like crayfish, mollusks such as snails and clams (Family Sphaeriidae), aquatic earthworms, spiders, and various insects and their larvae. Notable insect larvae in their diet include beetles (Order Coleoptera) mayflies (Order Ephemeroptera), a number of fly families in the Order Diptera (Tipulidae, Chironomidae, Culicidae, Tabanidae), stoneflies (Order Plecoptera), and megalopterans (Order Megaloptera). While adults can consume reptiles like lizards and water snakes Nerodia , as well as other amphibians, including small frogs and tadpoles. Jensen t al. (2008) examined the stomach contents of 100 amphiumas found no evidence of dragonfly naiads, salamander larvae, frog tadpoles, or small fish, despite these taxa coexisting with amphiumas.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • insectivore insectivore
  • eats non-insect arthropods
  • vermivore

• Animal Foods
• insects
• terrestrial non-insect arthropods
• mollusks
• terrestrial worms
• aquatic or marine worms
• aquatic crustaceans
• other marine invertebrates

Predation

One-toed amphiumas’ main predators are adult mud snakes ( Farancia abacura ) and rainbow snakes ( Farancia erytrogramma ). Other animals like cottonmouth snakes ( Agkistrodon piscivorus ), kingsnakes ( Lampropeltis ), plain-bellied watersnakes ( Nerodia erythrogaster ), American alligators ( Alligator mississippiensis ) and North American river otters ( Lontra canadensis ) will also prey on them. One-toed amphiumas living in drying ponds or lakes are often killed by feral hogs ( Sus scrofa ) that dig around in the mud. Sandhill cranes ( Antigone canadensis ) have been known to feed on two-toed amphiumas ( Amphiuma means ). Two-toed amphiumas have also been reported to feed on conspecifics living in the same range.

One-toed amphiumas’ major anti-predator mechanism is their cryptic behavior. Their nocturnal behavior and burrowing lifestyle provide them with the most protection because they’re harder to see or detect. Amphiumas have a strong bite that can inflict serious wounds on potential predators and may whistle when agitated. One-toed amphiumas can produce slimy mucus that makes them difficult to grasp. This mucus has also been observed to have a bitter taste and a slight numbing effect.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

In the food web, one-toed amphiumas prey on a variety of small amphibians and invertebrates while serving as a food source for larger predators like alligators, snakes, and wading birds. Means et al. (2020) studied the gastrointestinal tracts of 96 wild-caught one-toed amphiumas. They reported that nematodes in the digestive tract were the most common parasite. Less commonly, they discovered trematodes, cestodes, and acanthocephalans. They did not identify the parasites beyond these wide categories. One-toed amphiumas impact their ecosystem by burrowing, which aerates the soil allowing air and water to percolate into the soil.

• Ecosystem Impact
• soil aeration soil aeration

Economic Importance for Humans: Positive

One-toed amphiumas have no reported positive economic impact on humans.

Economic Importance for Humans: Negative

One-toed amphiumas have no reported negative economic impact on humans.

Conservation Status

One-toed amphiumas were listed as a species of “Near Threatened” on the IUCN Red List in 2020, but as of 2021 they are now listed as “Least Concern”. They have no special status on the US Federal List, CITES, and are not included on the State of Michigan List. One-toed amphiumas are listed as “Critically Imperiled” in Mississippi, Alabama, and Georgia and “Vulnerable” in Florida.

One-toed amphiumas are experiencing a decreasing population trend due to numerous human activities. Residential and commercial development, along with mining, and logging contribute significantly to environment degradation. Water quality is also threatened by pollution from silviculture, agriculture, industry, and urban sources. One-toed amphiumas are at risk due to habitat loss caused by groundwater disturbance and power plant waste dumping.

One-toed amphiumas inhabit several preserved areas. Their distribution overlaps with many protected lands such as state parks, national wildlife refuges, wildlife management areas, conservation areas, and nature preserves. To maintain amphiuma populations, conservation should focus on the preservation of drainage basins and wetlands where they reside. Due to their burrowing and nocturnal habits, surveys are helpful to determine one-toed amphiumas presence and the current condition of their habitat on these preserved lands. Identifying potential territories can help focus conservation efforts in these areas. Preventing habitat pollution such as runoff from agriculture, industry, and urban areas, is essential to protecting their environment.

Additional Links

AmphibiaWeb

Encyclopedia of Life

Contributors

Alana Williams (author), Radford University, Natalie May (editor), Radford University, Alexander McVicker (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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