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Necturus punctatus (Gibbes, 1850)
Harold A. Dundee1
1. Historical versus Current Distribution. Dwarf waterdogs (Necturus punctatus) are found in Atlantic Coastal Plain streams from the Chowan River in southeastern Virginia through North Carolina, South Carolina, and Georgia to the Ocmulgee–Altamaha River systems in southeastern Georgia (Bishop, 1943; Seyle, 1985c; Dundee, 1998; Petranka, 1998). Dundee (1998) mentions two small gaps within the distribution: in the lower reaches of the Pee Dee River in South Carolina and in several streams in the southeastern corner of South Carolina. These may be true absences or reflect a lack of collecting effort. Dwarf waterdogs typically occur in small streams and relatively shallow water, whereas the lower reaches of streams normally are deep.
2. Historical versus Current Abundance. Unknown. Populations probably persist in most areas of the historical range. Recent records from several Virginia counties (Tobey, 1985; Roble et al., 1999) suggest that the species occupies areas that probably have long harbored dwarf waterdogs. Despite stream pollution, they occur widely throughout their range, which also suggests that they occur where earliest records were noted. Traditional collecting methods of seining, dip netting, hook and line fishing, and minnow trapping have been augmented by the use of rotenone and electroshocking, thus allowing a more comprehensive discovery of distribution and habitat.
3. Life History Features.
A. Breeding. Reproduction presumably is aquatic because that is the typical pattern for Necturus spp., and all dwarf waterdogs have been found in aquatic habitats. Oocyte number increases with size (Meffe and Sheldon, 1987). Mid-autumn ovaries contained yolked and unyolked oocytes; males showed signs of sexual activity—large, firm, yellow testes with heavy dark pigmentation, involuted vasa deferentia, and swollen cloacal glands (Meffe and Sheldon, 1987). Bishop (1943) suggests a long breeding season, but likely most hatching takes place in winter. Neill (1963) found that dwarf waterdogs are most active during the winter when water is cold and streams are swollen.
i. Breeding migrations. Little is known of breeding in dwarf waterdogs; nests have not been discovered and no study has been made of tagged individuals.
ii. Breeding habitat. Unknown, but surely in water.
i. Egg deposition sites. Nests have not been discovered. Females likely attach their eggs to the undersides of logs and other objects lying in the water.
ii. Clutch size. Gravid females contain 15–55 ova (most between 20 and 40), and ova number is positively correlated with female size. Folkerts (1971) reported a gravid female collected on 12 April with 33 ovarian eggs; average egg diameter was 4.2 mm (other females in this sample had previously oviposited). Meffe and Sheldon (1987) found a single female on 20 February that had ovarian eggs averaging about 4 mm diameter. From these data, mating presumably occurs during the winter (Meffe and Sheldon, 1987; Petranka, 1998).
i. Length of larval stage. At least 2 yr (Bishop, 1943). The smallest known larva was 28 mm TL and was collected on 30 November; 40 mm TL larvae, presumably young of the year, were also collected at that time (Bishop, 1943).
ii. Larval requirements. Shallow water and leaf beds and a suitable source of food.
a. Food. Oligochaetes, aquatic Crustacea, especially ostracods (24.6%), various Insecta, particularly the dipterans Simuliidae (12.3%), Ceratopogonidae (24.6%), and beetles (Dytiscidae, 12.3%; Braswell and Ashton, 1985). Similarly, Folkerts (1971) examined six immature specimens and found they had eaten annelids, millepedes, amphipods, and insects, especially caddisfly larvae.
b. Cover. Larvae live in both shallow and deeper waters (Brimley, 1924) and will burrow in silt (Martof et al., 1980).
iii. Larval polymorphisms. Most larvae are brown but gradually change to gray when they are 40–50 mm SVL (Folkerts, 1971).
iv. Features of metamorphosis. Metamorphosis does not occur; only maturation of the reproductive system signifies change from larva to adult.
v. Post-metamorphic migrations. Unknown.
vi. Neoteny. Dwarf waterdogs have a larval structure, but no experiments have checked their response to metamorphic stimulating hormones. Thyroxin will cause reduction of gill and fin size in mudpuppies (Necturus maculosus); although these salamanders produce substantial amounts of thyroxin, they are essentially immune to this metamorphic agent and are thus permanently neotenic. The same likely applies to dwarf waterdogs.
D. Juvenile Habitat. Juveniles apparently prefer shallower water than adults (Folkerts, 1971) and are most common in mats of leaves.
E. Adult Habitat. Permanently aquatic and apparently only in streams. Bishop (1943) reported that they are usually found in the slower regions of streams, including side ditches, having mud or sandy banks/bottoms. These streams are usually small to medium sized. Dwarf waterdogs are most common in deeper sections with reduced flows and an accumulation of mud, silt, and leaves (Folkerts, 1971; Meffe and Sheldon, 1987). Individuals are rarely found in the main channels of the Neuse and Tar rivers (Braswell and Ashton, 1985; Petranka, 1998). A univariate analysis of habitat use based on water depth, water velocity, stream width, and substrates is presented in Meffe and Sheldon (1987).
F. Home Range Size. Unknown.
G. Territories. Unknown, but the numbers collected at given sites and habitats suggest that territorial behavior is not exhibited.
H. Aestivation/Avoiding Dessication. Unknown, but most animals reported were taken in the cooler months of October–April.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). Adults are active during wintertime and will aggregate in leaf beds (Brimley, 1924; Martof et al., 1980).
K. Interspecific Associations/Exclusions. Dwarf waterdogs and Neuse River waterdogs (Necturus lewisi) exhibit a strong dietary overlap and likely compete with each other for food resources in North Carolina in areas where they are syntopic (Braswell and Ashton, 1985) . Other associates include lesser sirens (Siren intermedia), many-lined salamanders (Stereochilus marginatus), several species of fishes, and flattened nymphs of the dragonfly Hagenius brevistylus (Folkerts, 1971).
L. Age/Size at Reproductive Maturity. Dwarf waterdogs reach sexual maturity between 65–70 mm SVL (Hecht, 1958). Folkerts (1971) suggests most individuals become sexually mature during their fifth year.
M. Longevity. A wild-caught animal lived for a little over 5 yr, 8 mo at the Cincinnati Zoo (Snider and Bowler, 1991). If the animal was adult when caught, then Folkerts' estimate of sexual maturity at 5 yr would indicate a longevity in excess of 10 yr.
N. Feeding Behavior. Braswell and Ashton (1985) showed that in sites sympatric with Neuse River waterdogs, adult dwarf waterdogs consumed gastropods (15%), pelecypods, oligochaetes, arachnids, isopods especially (22.2%), plus cladocerans, ostracods, copepods, amphipods, chilopods, and various insect families and orders, especially Trichoptera (22.2%). Prey of adults generally includes other species of salamanders, annelids, crayfish, and insects such as mayflies and chironomids (Brode, 1969; Fedak, 1971; Folkerts, 1971; Meffe and Sheldon, 1987; Gibbons and Semlitsch, 1991). Plant material was also present, although this could have been ingested incidentally (Meffe and Sheldon, 1987). During the breeding season, 54% of adults had empty stomachs, suggesting that some adults either cease feeding or reduce their feeding activity at this time (Meffe and Sheldon, 1987). In March–April many stomachs were empty, suggesting dwarf waterdogs do not feed during the breeding season (Folkerts, 1971). A high percentage of stomachs were empty in mid October to mid November, perhaps as a prelude to the breeding season (Meffe and Sheldon, 1987). Folkerts (1971) suggested that feeding may be nocturnal and digestion completed before the daytime collecting. He also suggested that larvae may feed throughout the year. A partially digested, unidentifiable salamander found in one stomach suggests cannibalism (Meffe and Sheldon, 1987).
Prey of juveniles includes annelids (especially earthworms), amphipods, millipedes, and insects such as caddisfly larvae (Folkerts, 1971).
O. Predators. According to Petranka (1998), predators have not been identified but likely include fishes. Unless dwarf waterdogs produce toxic skin secretions, the animals associated with their habitat that are predatory, hence enemies, could include predaceous aquatic insects, crayfish, water snakes, and large salamanders such as Sirens, Amphiumas, and Neuse River waterdogs. In captivity, Neuse river waterdogs are aggressive towards dwarf waterdogs and will viciously bite them (Petranka, 1998).
P. Anti-Predator Mechanisms. Unknown. Neuse River waterdogs are suspected to produce noxious secretions (Brandon and Huheey, 1985), but this has not been studied in dwarf waterdogs. Escape to hiding places in undercut stream banks or amid debris would seem to be likely ways to avoid predators.
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. Populations likely persist in most areas of the historical range. Recent records suggest that the species occupies areas that probably have long harbored dwarf waterdogs (Tobey, 1985; Roble et al., 1999). Despite stream pollution, they occur widely throughout their range, which also suggests that they occur where earliest records were obtained.
1Harold A. Dundee
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 24 Feb 2017.
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