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.
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.
Anti-predator Adaptations: cryptic
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.
Range length: 15.2 to 23 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; poisonous
Sexual Dimorphism: sexes alike
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.
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.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: rivers and streams
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.
Biogeographic Regions: nearctic (Native )
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.
Animal Foods: amphibians; fish; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms
Primary Diet: carnivore (Eats non-insect arthropods)
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.
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.
Positive Impacts: research and education
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.
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.
Development - Life Cycle: neotenic/paedomorphic; metamorphosis
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.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: near threatened
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.
Communication Channels: visual ; tactile ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; chemical
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.
Mating System: monogamous
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.
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.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization
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.
Parental Investment: male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female)
The Neuse River waterdog (Necturus lewisi) is a medium-sized waterdog, family Proteidae, found in two rivers of North Carolina.
The range of the Neuse River waterdog is limited to the Neuse and Tar-Pamlico River basins in the eastern Piedmont and Coastal Plain of North Carolina.
N. lewisi has a rusty-brown dorsal side with many large, bluish-black spots. The ventral side is dark brown to grey and also spotted. The snout is compressed dorsally and truncated. The tail is compressed laterally and ridged. Each hind limb has four toes, and the gills are dull red and bushy. Sexually active males have sowled cloacae and two enlarged cloacal papillae that point to the rear. Males and females are of a similar size. Adults measure 16.5–28.0 cm from the tip of snout to tip of tail. The young possess a dorsal stripe along their length along with a dark lateral stripe.
Males and females become sexually mature after reaching 102 mm and 100 mm, respectively, measured from tip of the snout to the posterior end of the cloaca. This size is reached at 5.5 years in males and 6.5 years in females.
Neuse River waterdogs prefer streams with a flow>10 cm/s and streams which are>15 m wide, and 1 m deep, in areas with a hard clay or soil bottom, as well as areas covered with leaf bed. Larvae are found in leaf beds of quieter waters which provide cover and foraging sites. Males have a greater range than females, and both males and females increase their range after moderate rains, but decrease it after large rains (>40 mm). During winter, adults mostly reside in burrows in banks or under granite rocks. During the spring, the adults move to large bedrock outcrops or beneath large boulders in relatively fast current where nesting occurs. Home ranges contain animal burrows or rock overhangs, large flat rocks on sand gravel substrates, and slack-water areas with detritus mats of leaves.
Adults create retreats by shoveling sand and gravel with their snouts, forming a cavity beneath cover objects. Sometimes, gravel is picked up in the mouth and moved to the periphery of the retreat. Entrances to these retreats face downstream. Females, and to a lesser extent males, actively defend their retreats from intruders. Threat displays include flaring and pulsating the gills and curling the upper lip. Intruders which do not flee after this display are attacked and bitten, usually on the end of the tail.
Males have sperm in the vasa deferentia from November through May, and females have been found with this sperm from December through May. Females move to nesting sites beneath fast-moving current during the spring. Oviposition occurs in April and May, corresponding to the time when ovarian eggs reach their maximum size. Eggs are 8–9 mm in diameter and attach to the substrate by a blunt stalk.
A pair of Neuse River waterdogs crawl slowly, with the male trailing the female by 2–4 cm. The male positions his snout behind the rear legs of the female when she stops. The female has her gills flared, while the male has his close to the neck. The male then moves across her body at the base of her tail. Once parallel, the male begins to stroke the female with his chin. This stroking begins at the top of the head, moves roughly halfway down the female and back to the head. The female then raises her head each time the male's chin contacts her neck or head. This sequence repeats many times over a period of roughly 18 minutes. The male then circles the female in a clockwise direction while maintaining contact with her. After several slow circles are made, the males moves parallel to the female and places his limbs over her back. The pair remains in this position for 30 minutes and retreats.
Adults feed from the mouths of their retreats or move about in search of prey at night. Olfaction and sight play important roles in locating food. Animals are active away from cover at night, and also during raised water levels and increased turbidity. Individuals are inactive when stream temperatures exceed 18 °C.
Adults mainly prey on snails, earthworms, isopods, amphipods, mayflies, stoneflies, caddisflies, true flies, and fish. Other prey include: slugs, leeches, spiders, crayfish, centipedes, millipedes, odonates, hellgrammites, beetles, caterpillars, and salamanders. Prey of larvae are mainly ostracods, copepods, mayflies, true flies, and beetles. Other prey items of larva include: earthworms, caldocerans, isopods, amphipods, collembolans, odonates, and stoneflies along with other insects.
Mainly preyed on by fish, Neuse River waterdogs produce chemical defenses to ward off these predators.
The Neuse River waterdog (Necturus lewisi) is a medium-sized waterdog, family Proteidae, found in two rivers of North Carolina.
.jpg)
