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Mudpuppy – Necturus maculosus
The common mudpuppy salamander “the waterdog” is known as Necturus maculosus. They are one
of only a few salamanders that make noise. They get their name from the somewhat embellished
notion that their squeaky vocalizations sound like a dog's bark. They are in the Order Caudata, which
along with the Order Anura (frogs & toads) and Order Gymnophiona (caecilians) make up the
Amphibian group. Salamanders, newts, frogs and toads are also known as tetrapods. The word
"Tetrapoda" means "four legs" in Greek. Tetrapods include all land-living vertebrates. Tetrapods are
part of a larger group called Sarcopterygii, which also includes several groups of lobe-finned fish, such
as lungfish and the coelacanth.
Physical Description:
Salamanders and newts are the least specialized amphibians in the body form and location. Their
bodies are elongated and stout, with well-developed axial muscles (head and neck) and muscular tail.
Salamanders use their limbs in combination with the side to side body undulations characteristic of a
fish, and thus probably resemble the earliest land vertebrates in location. Larval salamanders are well
adapted for an aquatic existence. Mudpuppies have a lateral line system consisting of pressure, motion,
and electroreceptor sensory cells triggering fast escape. They have large feathery, external gills at the
back of their heads. The gills have an enormous surface area which allows direct respiratory exchange
between the larvae and the surrounding water. Larval salamanders also have an enlarged, fleshy fin
along the dorsal and ventral surfaces of their tail that enables them to swim more efficiently. Adult
Mudpuppies have flat heads, wide tails, stubby legs, and feet with four distinct toes. Their bodies are
gray or brownish-gray with blue-black spots.
Mudpuppies, like all families of salamanders are neotenic. Neotenic salamanders retain their larval,
filamentous external gills, two pairs of pharyngeal slits and caudal fins as adults. Non-neotenic
amphibians completely loose these juvenile features as they go through the process of metamorphosis
losing their gills and moving completely changing over to pulmonary respiration (lungs). In an aquatic
environment external gills are more efficient at exchanging gases than are internal lungs so selective
pressures have favored those animals that retained their gills through metamorphosis.
Curiously, mudpuppies have lungs but they use them to maintain buoyancy in the water much as a fish
uses its swim bladder. Mudpuppies never lose the large fleshy fins on their tail either. Since the adults
are aquatic, this large fleshy fin fold enables them to swim more efficiently.
Reproduction:
Females lay large clutches of eggs and guard them until they hatch, a unique trait among salamanders.
Mudpuppies mature at four to six years and can live to be more than twenty years old. Mudpuppies
breed once a year. When males are ready to breed, their cloacas become swollen. Males deposit their
sperm in the substratum of the environment. The female will then pick them up with her cloaca and
store them in a small specialized gland, a spermatheca, until the eggs are fertilized. Females store the
sperm until ovulation and internal fertilization take place, usually just prior to deposition in the spring.
Before the eggs are deposited, male mudpuppies leave the nest. Once ready, the female will deposit
the eggs in a safe location, usually on the underside of a rock or log. They can lay anywhere from 20–
200 eggs, usually an average of 60. The eggs are shell-less and have no pigment. The mother will stay
with her eggs during the incubation period (approximately 40 days). Hatchlings are about 2.5 cm and
grow to 3.6 cm before the yolk is completely consumed. After six years of maturing, the mudpuppies
are able to repeat this reproduction cycle.
Habitat, Behaviors & Diet:
Mudpuppies are solitary animals, coming together only to reproduce in the fall. They are active
throughout the year, and do not hibernate. Mudpuppies live on the bottoms of lakes, ponds, rivers, and
streams, and never leave the water. They hide themselves in vegetation and under rocks and logs,
emerging at night to feed on whatever prey. Mudpuppies are nocturnal creatures and only come out
during the day if the water they live in is murky. Mudpuppies are carnivores and will eat a variety of
aquatic organisms. They are opportunistic feeders and will eat whatever they can catch. Crayfish are a
major part of their diet. They also eat insect larvae, small fish, fish eggs, aquatic worms, snails, and
other amphibians are also eaten. They will also eat carrion and are often caught in traps that are baited
with dead fish. Mudpuppies have two rows of teeth that they use to eat their prey. At both sides of
their mouths their lips interlock which allows them to use suction feeding.
Predators:
The mudpuppy has few predators but may include fish, larger crayfish, turtles, and water snakes.
Because fisherman frequently catch and discard them by accident while fishing, humans are considered
to be one of their main predators.
Theories of Neoteny:
There are theories that there is a biological significance to which salamanders are the only amphibians
to do neoteny behavior. Based on many studies neoteny basically enables salamanders to avoid the
terrestrial environment it its conditions are too inhospitable. In the case of predation, if there are a lot
of predators living on the land which feed on a particular salamander species, it would make sense for
the salamanders to spend as much time as possible in an aquatic environment.
Pre-Lab Questions:
1. What is the binomial name of the mudpuppy?
2. What Order of Amphibians do mudpuppies belong to?
3. What does tetrapod mean?
4. Describe the bodies of salamanders and newts.
5. What are the physical characteristics of mudpuppies?
6. What does neoteny mean?
7. Why are mudpuppies neotenic?
8. What do the mudpuppies use their lungs for?
9. How old is the average sexually mature adult?
10. What type of reproduction occurs in mudpuppies? Does this involve actual sex?
a. How is this reproduction different than other animals like reptiles, birds and mammals
that truly have “sex”?
b. Are mudpuppies oviparous, ovoviviparous or viviparous? Where would you find the
eggs?
11. What are mudpuppies social behaviors – during non-mating seasons and during mating seasons?
12. What is the habitat of mudpuppies?
13. Are mudpuppies active during the day or night?
14. Do mudpuppies hibernate during the cold months?
15. What is the typical diet of mudpuppies?
16. What are the common predators of mudpuppies?
17. Why are humans also considered to be predators?
18. What are the theories of why mudpuppies never do complete metamorphosis like other
amphibians, and remain neotenic?