Necturus lewisiNeuse River Waterdog

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Geographic Range

Populations of Necturus lewisi are endemic to North Carolina in the United States. More specifically, these amphibians reside in parts of Craven, Durham, Franklin, Granville, Johnston, Lenoir, Nash, Orange, Vance, and Wake counties, around 35°N latitude. They reside in the Neuse and Tar-Pamlico river basins and research has been conducted on these animals in the Little River, a tributary of the Neuse River. ("Conservation of the Amphibia of the United States: A Review", 1980; Ashton, 1985; Braswell and Ashton, 1985; Cooper and Ashton, 1985)

Habitat

Necturus lewisi lives in freshwater streams; none have been found in lakes or ponds. Requiring clean, fresh water, populations of this aquatic amphibian are most prevalent in streams that are wider than 15 meters, deeper than 100 cm, and have a flow rate of greater than 10 cm per second. Both juveniles and adults dwell in loose granite rocks and sand or gravel areas as well as under bedrock from the stream banks.

The salamanders develop home retreat areas free of debris and algae. In order to move sand and gravel, they shovel it with their snout and carry it in their mouths.

Preferred habitats vary with the season, temperature, dissolved oxygen content, flow rate of the water, and the precipitation. (Ashton, 1985; Braswell and Ashton, 1985)

  • Aquatic Biomes
  • rivers and streams

Physical Description

Hatchlings have rounded heads, compared to the square, elongated heads of the adults. The mean length of hatchlings is estimated to be 22.8 mm long. They feature dark, well-formed eyes and developed forelimbs. Often on the forelimbs, three of the toes are complete and the fourth, inner toe is only a bud. The hindlimbs may not be fully developed and pressed close to the lower tail fin. They are light brown in color with dark lines from each nostril to the gills, and a white patch (approximately the size of their eye) behind and above the eye. They have melanophores on the gills, upper surfaces of the legs, lower jaw, and parts of the head, with concentrations highest in the area of the tail.

Studies have found that about 48% of the post-hatchling larvae have a dark lateral stripe while the rest have dark, poorly defined sides. Most have a broad, light tan, dorsal stripe from the snout to the tail. Along the dorsal region are small, dark (but poorly defined) spots. The underside of the larvae is white, or has a faint network of lines. After a year, the larvae measure 30 mm in length.

Adults lose the striped pattern; the side melanophores decrease in intensity while the dorsal melanophores increase in intensity and definition. The melanophores are dark, while the rest of the skin is reddish brown. Individuals with a SVL (snout vent length, measured from the tip of the snout to the vent) of 63 mm are considered adults. Adults have a set of bushy, red gills (gills are present in juvenile forms as well), as well as a set of weak lungs. Their tail is laterally compressed and they lack the fins present in the hatchlings. Adults have four toes on each foot. Neuse River waterdogs contain low levels of toxins in their skin to deter predators.

A major difference between the larvae of N. lewisi and other members of the genus Necturus is the difference in pigmentation. Necturus maculosus contains a dark dorsal area bordered by a thin, light, lateral stripe, while Necturus punctatus are uniformly gray with no striping pattern. The difference in the larvae adds to the evidence that N. lewisi is a distinct species. ("Conservation of the Amphibia of the United States: A Review", 1980; Ashton and Braswell, 1979; Gilbert, 1977; Petranka, 1998)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    15.2 to 23 cm
    5.98 to 9.06 in

Development

Neuse River waterdogs hatch from eggs between April and July. Hatchling development lags on their hindlimbs and on a fourth toe on their forelimbs. During the transition from hatchling to larvae, the animals lose their tail fins and tadpole-like belly and develop fully formed hindlimbs. The transition from larvae to adult includes change in distribution of melanophores, and therefore, coloration, as well as an increase in size and length. After 5.5 to 6.5 years, the waterdog is sexually mature and capable of reproduction. Waterdogs can reach a total length of 23 cm and retain the use of their gills as adults. ("Conservation of the Amphibia of the United States: A Review", 1980; Adams, 1926; Ashton and Braswell, 1979)

Reproduction

Courtship between males and females begins near the female's home retreat and lasts for about 1 hour. The male follows the female around, roughly 2 to 4 cm from her tail. When the female stops moving, the male crawls so its snout is behind a hindlimb of the female. At this time, the female's gills flare, while the male's retract. While the female is motionless, the male moves across the female's body and strokes her with his chin. Now, both the male's and female's gills flare and pulsate. The male then circles the female, while maintaining contact with her body, finally lying parallel to the female.

Males and females mate during fall and winter. During mating season, the male's vent inflames. Males contain two papillae that enable the deposition of spermatophores into the female's spermathecae, which hold the sperm until the following spring. After eggs are laid, both parents guard the nest. (Ashton, 1985; Pudney, et al., 1985)

Neuse waterdogs reach sexual maturity at around 5.5 to 6.5 years or at a SVL (snout vent length, measured from the tip of the snout to the vent) of 102 mm for males and 100 mm for females. Breeding once per year, males and females mate during fall and winter and spawn in the spring. After displays of courtship, males deposit a packet of sperm, which the female then places into her vent. Egg fertilization occurs internally and during the spring, females will lay a clutch of eggs and both the male and female will guard the nest. Females lay between 25 and 90 eggs. (Adams, 1926; Cooper and Ashton, 1985; Pudney, et al., 1985)

  • Breeding interval
    Neuse River waterdogs breed once yearly.
  • Breeding season
    Mating occurs during the fall and winter; egg depositation occurs in May or June.
  • Range number of offspring
    25 to 90
  • Average number of offspring
    75
  • Range age at sexual or reproductive maturity (female)
    5.5 to 6.5 years
  • Range age at sexual or reproductive maturity (male)
    5.5 to 6.5 years

After displays of courtship during the mating period, females allow males into their home retreat area. During the spring, when the pair creates a nest for the eggs, both sexes guard the nest until the young hatch. Because of the large clutch size, gamete production is the most significant parental investment. (Adams, 1926; Ashton, 1985; Pudney, et al., 1985)

Lifespan/Longevity

Research has not been conducted on the longevity of Necturus lewisi. However, its relative Necturus maculosus, which resides in the Central United States and Canada, may live for 30 or more years. (McDaniel, et al., 2009)

Behavior

Home retreat areas are developed by waterdogs within 24 hours of exposure to a new environment. They push and carry gravel around to create an oval shaped area, usually with a diameter two-thirds the size of the animal. The opening of the area is often on the downstream side of the rock or covering.

In a study in 1985, waterdogs were presented with algae covered rocks, which were cleaned within 48 hours and converted into a home retreat area.

Nuese River waterdogs are active at night, and leave their retreats in search of food. There is no evidence of migrational movements in this species. (Ashton, 1985)

  • Range territory size
    17 to 73 m^2

Home Range

Home ranges of waterdogs often overlap, regardless of the sex or season. Males have a significantly larger home range than females; 73 square meters for males compared with 17 square meters for females. (Ashton, 1985)

Communication and Perception

Waterdogs defend their territories from intruders by flaring their gills. If an intruder advances, the flared gills pulsate and the waterdog curls its upper lip. During a confrontation, false attacks are displayed before actual contact is made. Bites serve as warnings which usually cause little damage to the intruder. Seventy-five percent of bites occur at the base of the tail.

Olfactory cues also protect territory. Areas with the scent of another animal, even if the animal is not physically present, are strongly avoided by intruders.

Stalking prey involves both visual and olfactory senses.

The observation that males rub the females with their chins during courtship suggest that pheromones may play a role in communication during breeding. (Ashton, 1985; Braswell and Ashton, 1985; Pudney, et al., 1985)

Food Habits

Animals from the genus Necturus eat crayfish, insect larvae and nymphs, crustaceans, mollusks, plant remains, and worms.

Seventy-four percent of the diet of adult Necturus lewisi consists of arthropods. The waterdogs also eat mollusks, crayfish, shrimp, earthworms, Plecoptera nymphs, Odonata naiads, and some small fish including darters and pirate perch. On one occasion, scientists discovered an adult worm snake (Carphophis amoenus) inside the salamander. However, scientists noted that only the tail showed signs of digestion.

The larvae, which are often not large enough to consume some aquatic organisms, eat arthropods (approximately 99% of their diet), including ostracods and copepods.

The lack of Ceratopogonidae in the larvae N. lewisi diet distinguish N. lewisi from N. punctatus, its close relative. The adult N. punctatus do not eat vertebrates while the adult N. lewisi do.

Since the diet varies from season to season, based on prey availability, Neuse River waterdogs are an opportunistic feeder. Hunting for their prey requires both sight and olfactory senses, which they use to discern movement from a meter away. When hunting, which usually occurs at night, waterdogs stalk the prey, then stop within striking distance (approximately 2 to 3 cm). If the prey moves, the waterdog attacks and swallows the prey. Larger prey are sometimes regurgitated and then re-swallowed. All prey are ingested whole. ("Conservation of the Amphibia of the United States: A Review", 1980; Adams, 1926; Braswell and Ashton, 1985)

  • Primary Diet
  • carnivore
    • eats non-insect arthropods
  • Animal Foods
  • amphibians
  • fish
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms

Predation

While waterdogs eat small fish, larger fish prey on waterdogs. In order to avoid predators, waterdogs avoid hunting and leaving the cover of their home retreat area until nightfall. They also have toxins in their skin to deter predators. Their cryptic coloration likely aids in avoiding predators as well. (Brandon and Huheey, 1985; Brandon and Huheey, 1985; Brandon and Huheey, 1985)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Neuse River waterdogs are predators on many organisms including mollusks, crayfish, shrimp, earthworms, insects, and some small fish. The prey are found in a variety of areas, including flowing water, slack water, leaf beds, under logs and rocks, and in sand and gravel.

To avoid predators, such as fish, the waterdogs hunt for food at night.

Studies have shown that when Necturus punctatus occupies the same tank as N. lewisi, N. lewisi will attack and eat its smaller relative. (Ashton, 1985; Brandon and Huheey, 1985; Braswell and Ashton, 1985)

Economic Importance for Humans: Positive

Small and easy to care for, the genus Necturus is often used in research and education. Since it represents a rather simple tetrapod, it is often used for teaching anatomy. It is also a textbook example of paedomorphosis. Waterdog ancestors probably had well-developed lungs; now they require gills to respire. (Adams, 1926)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no documented adverse effects of Necturus lewisi on humans.

Neuse River waterdogs do contain toxins within their skin, however, levels of the toxin are not enough to affect humans. Some believe Neuse River waterdogs bring bad luck. (Brandon and Huheey, 1985; Braswell and Ashton, 1985)

Conservation Status

Because they require clean, flowing water and larger streams, Neuse River waterdogs are listed as a species of "special concern" in North Carolina. Destruction of its habitat through the creation of dams and pollution of the rivers threaten this species. ("Conservation of the Amphibia of the United States: A Review", 1980)

Other Comments

Necturus lewisi was first recognized as a distinct subspecies in 1924 by C.S. Brimley. He named the animal after Frank B. Lewis, who provided him with many specimens. (Cooper, 1979)

Contributors

Cynthia Lai (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

poisonous

an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

References

United States Department of the Interior Fish and Wildlife Service. Conservation of the Amphibia of the United States: A Review. 134. Washington D.C.: United States, Fish and Wildlife Services. 1980. Accessed April 03, 2010 at http://www.nwhc.usgs.gov/disease_information/amphibian_malformation_and_decline/amphibian_conservation_1980.pdf.

Adams, L. 1926. Necturus: A Laboratory Manual. New York: J. J. Little and Ives Company.

Ashton, R. 1985. Field and Laboratory Observations on Microhabitat Selection, Movements, and Home Range of Necturus lewisi (Brimley). Brimleyana, 10: 83-106.

Ashton, R., A. Braswell. 1979. Nest and Larbae of the Neuse River Waterdog, Necturus lewisi (Brimley) (Amphibia: Proetidae). Brimleyana, 1: 15-22.

Brandon, R., J. Huheey. 1985. Salamander Skin Toxins, With Special Reference to Necturus lewisi. Brimleyana, 10: 75-82.

Braswell, A., R. Ashton. 1985. Distribution, Ecology, and Feeding Habits of Necturus-Lewisi (Brimley). Brimleyana, 10: 13-36.

Cooper, J., R. Ashton. 1985. The Necturus lewisi Study: Introduction, Selected Literature Review, and Comments on the Hydrologic Units and Their Faunas. Brimleyana, 10: 1-12.

Cooper, J. 1979. The Brothers Brimley; North Carolina Naturalists. Brimleyana, 1: 1-14.

Gilbert, S. 1977. Pictorial Anatomy of the Necturus. Seattle: University of Washington Press.

McDaniel, T., P. Martin, G. Barrett, K. Hughes, A. Gendron, L. Shirose, C. Bishop. 2009. Relative Abundance, Age Structure, and Body Size in Mudpuppy Populations in Southwestern Ontario. Journal of Great Lakes Research, 35 (2): 182-189.

Petranka, J. 1998. Salamanders of the United States and Canada. Washington: Smithsonian Institute Press.

Pudney, J., J. Canick, G. Callard. 1985. The Testis and Reproduction in Male Necturus, with Emphasis on N. lewisi (Brimley). Brimleyana, 10: 53-74.