Common mudpuppy Temporal range: Paleocene - Recent[1]
Conservation status
Least Concern  (IUCN 3.1)[2]
Secure  (NatureServe)[3]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Urodela
Family:	Proteidae
Genus:	Necturus
Species:	N. maculosus
Binomial name
Necturus maculosus (Rafinesque, 1818)
Range of N. maculosus
Synonyms
Sirena maculosa Rafinesque, 1818

The common mudpuppy (Necturus maculosus) is a species of salamander in the family Proteidae.^[4] It lives an entirely aquatic lifestyle in parts of North America in lakes, rivers, and ponds. It goes through paedomorphosis and retains its external gills.^[5] Because skin and lung respiration alone is not sufficient for gas exchange, the common mudpuppy must rely on external gills as its primary means of gas exchange.^[6] It is usually a rusty brown color^[7] and can grow to an average total length (including tail) of 13 in (330 mm).^[8] It is a nocturnal creature, and is active during the day only if the water in which it lives is murky.^[4] Its diet consists of almost anything it can get into its mouth, including insects, mollusks, and earthworms (as well as other annelids).^[7] Once a female common mudpuppy reaches sexual maturity at six years of age, she can lay an average of 60 eggs.^[7] In the wild, the average lifespan of a common mudpuppy is 11 years.^[9]

The common mudpuppy can be a rusty brown color with gray and black and usually has blackish-blue spots, but some albino adults have been reported in Arkansas.^[7] In clear, light water, their skin gets darker, likewise in darker water, their skin gets lighter in color.^[6] At sexual maturity, mudpuppies can be 20 cm (8 in) long and continue to grow to an average length of 33 cm (13 in), though specimens up to 43.5 cm (17.1 in) have been reported.^[8] Their external gills resemble ostrich plumes and their size depends on the oxygen levels present in the water. In stagnant water, mudpuppies have larger gills, whereas in running streams where oxygen is more prevalent, they have smaller gills.^[5] The distal portions of the gills are very filamentous and contain many capillaries.^[8] Mudpuppies also have small, flattened limbs which can be used for slowly walking on the bottoms of streams or ponds, or they can be flattened against the body during short swimming spurts.^[8] They have mucous glands which provide a slimy protective coating ^[5]

Mudpuppies are one of many species of salamanders that fail to undergo metamorphosis. Most hypotheses surrounding the origin of Necturus's lack of metamorphosis concern the effectiveness of the thyroid gland. The thyroid gland in some salamanders, like the axolotl, produce normal thyroid hormones (THs), but cells in the organism express thyroid hormone receptors (TR) that are mutated, and do not bond correctly with thyroid hormones, leading to some salamanders in a state of perpetual juvenile-hood.^[10] In contrast to axolotls, in mudpuppies, these THs are normally expressed. However, it is believed that instead of having TH-insensitive tissues that block the effects of THs, some mudpuppy tissues, such as the external gills, have lost the ability to be regulated by TH over time.^[11] This selective insensitivity to THs suggests a normal level of activity in the hypothalamo-pituitary-thyroid axis in developing mudpuppies, unlike other salamander species.

The common mudpuppy also does not have a parathyroid gland.^[12] The majority of salamanders with parathyroid glands rely on them to help with hypercalcemic regulation; hypercalcemic regulation in mudpuppies is primarily done by the pituitary gland instead.^[12] In common mudpuppies, the purpose of the absence of a parathyroid gland is poorly understood. One reason for the absence might be the lack of variability in the climate of mudpuppies, as the parathyroid glands of salamanders vary greatly depending on seasonal changes, or whether the organism hibernates.^[13]

Necturus maculosus specimens live in streams, lakes, and ponds in the eastern part of North America.^[5] They appear in the southern section of Canada, as far south as Georgia, and from the Midwest United States to North Carolina. Behaviorally, they hide under cover such as rocks and logs during the day and become more active at night.^[8] However, in muddy waters, the mudpuppy may become active during the day.^[4] Mudpuppies can even live under the ice when lakes freeze.^[4] There is an introduced population in Maine.^[14]

Mudpuppies use rows of teeth to eat their prey.^[6] Salamanders have three different sets of teeth: dentary, premaxillary, and vomerine teeth, which are named due to their location in the mouth.^[15] All the teeth, despite their different locations, are very similar. They are small and conical, meaning mudpuppies are homodonts due to their similar shape.^[16][17] The common mudpuppy never leaves its aquatic environment and therefore does not undergo morphogenesis; however, many salamanders do and develop differentiated teeth.^[18] Aquatic salamander teeth are used to hinder escape of the prey from the salamander; they do not have a crushing function.^[18] This aids the salamander when feeding. When the salamander performs the "suck and gape" feeding style, the prey is pulled into the mouth, and the teeth function to hold the prey inside the mouth and prevent the prey from escaping.^[15] At both sides of their mouths, their lips interlock, which allows them to use suction feeding.^[8] They are carnivorous creatures and will eat almost anything they can get into their mouths. Typically, they prey upon such animals as insects and their larvae, mollusks, annelids, crayfish, small fish, amphibians, earthworms, and spiders.^[19][20] The jaw of a mudpuppy also plays a significant role in its diet. The mudpuppy jaw is considered metaautostyly, like most amphibians, meaning the jaw is more stable and that the salamander has a dentary.^[16] This affects their diet by limiting the flexibility of the jaw to take in larger prey. The mudpuppy has few predators which may include fish, crayfish, turtles, and water snakes. Fishermen also frequently catch and discard them.^[7]

Mudpuppies take six years to reach sexual maturity.^[8] Mating typically takes place in autumn, though eggs are not laid till much later.^[5] When males are ready to breed, their cloacae become swollen. Males deposit their spermatophores 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.^[7] Females store the sperm until ovulation and internal fertilization take place, usually just prior to deposition in the spring.^[8] Before the eggs are deposited, male mudpuppies leave the nest.^[7] Once ready, the female deposits the eggs in a safe location, usually on the underside of a rock or log.^[8] They can lay from 20 to 200 eggs,^[5] usually an average of 60.^[7] The eggs are not pigmented and are about 5–6 mm (0.20–0.24 in) mm in diameter. The female stays with her eggs during the incubation period (around 40 days). Hatchlings are about 2.5 cm (0.98 in) long and grow to 3.6 cm (1.4 in) before the yolk is completely consumed.^[8]

The mudpuppy is a member of the genus Necturus, which is tentatively grouped with Proteus in the family Proteidae. A 1965 study done by Kezer et al.^[21] proposed that while these two genera were thought to exhibit parallel evolution, it is more likely that they both evolved from a common ancestor. Both have the same chromosome number, n=19, leading scholars to believe that they must be ancestors of an organism with a haploid number of 19 chromosomes. However, this grouping is a tentative inference favored by some scholars and opposed by others, as more recent studies of mitochondrial DNA sequences indicate that they are like distant relatives with shared morphology.

Drawing on allozymic data (information about enzymes that correspond to different alleles of a locus) and cytological data (information about the cells), Larson, Weisrock, and Kozak developed a phylogeny for the genus Necturus.^[22] Necturus maculosus, the common mudpuppy, is in a group with N. alabamensis and N. beyeri. Their group is sister to N. punctatus, and N. lewisi is the sister lineage of both these groups. They do note that the allozymic data slightly favors a sister grouping of N. alabamensis and N. beyeri relative to N. maculosus, while the cytological data groups N. beyeri and N. maculosus relative to N. alabamensis; because of this discrepancy, they approximate a three-way split. Also, they draw on an immunological data study (information about the immune bodies and system) by Maxson et al. (1988)^[23] to note that all living species of Necturus are estimated to share a common ancestor in the Pliocene.

Though this outline serves as a generally accepted model for the common mudpuppy's taxonomy, there have been several studies which pose new material and alterations. The taxonomy was refined most recently after a 2022 study discussing the discovery of a new proteid salamander species, Euronecturus grogu, that preceded N. maculosus. The findings challenge long-standing assumptions about the genus, particularly the belief that all Eurasian members originated from a single lineage that diverged from their North American relatives before the Oligocene.^[24] This gives insight into the geographic origins of the common mudpuppy species as perhaps a lineage developed in North America from an originally Eurasian salamander. In their taxonomy, Euronecturus grogu is sister to N. maculosus. This might be the common ancestor that Larson, Weisrock, and Kozak estimated all species of Necturus to share, though it estimated that Euronecturus grogu is from the miocene and they expected an ancestor from the pliocene. Despite time discrepancies, this recent study seems to indicate that their predictions were accurate to a significant degree.

Using mitochondrial DNA sequence data, K. Greenwald et al. analyzed the phylogeography of Necturus maculosus, determining its geographic origins for evolutionary analysis.^[25] They identified a significant split between eastern and western lineages in the regions of northern USA and southern Canada where mudpuppies are native, suggesting that the Mississippi River was a determinant factor in species distribution following the postglacial Pleistocene. Mudpuppies might have originated in the southern Mississippian region at some point after the glacial era, migrating and dispersing north to areas such as the Great Lakes using the river after northern glaciers had melted. The two populations that developed each have a single widespread and common haplotype, or group of genes inherited from a single parent, distinguishing them as definite lineages. This haplotype is also accompanied by several low-frequency yet closely related haplotypes, a phenomenon that occurs in many species that experience bottleneck events in formerly glaciated regions. There is sufficient data to support a distinction of mudpuppies in the Great Lakes basin as their own species.

Further evidence for species diversity within Necturus emerged in a 2017 study by Chabarria et al.,^[26] which examined mitochondrial DNA (ND2 gene) and head morphology. This research identified two distinct mitochondrial lineages within N. maculosus, consistent with earlier findings of geographic structuring. However, the study also highlighted subtle but significant variation in cranial shape between these lineages, suggesting that the taxon may be paraphyletic—that is, the current definition of N. maculosus may not encompass all descendants of a common ancestor. These results challenge the traditional understanding of the species' boundaries and support the hypothesis that N. maculosus comprises multiple distinct evolutionary lineages. The findings underscore the need for further morphological and genomic analysis to determine whether taxonomic revisions are warranted.

More insight into species diversity within Necturus emerged in a 2017 study suggesting that a new Necturus species was occurring in the Tennessee Valley, a region where the common mudpuppy was thought to be the only native Necturus.^[27] Prior to this, the common mudpuppy was not known to co-occur with any other congeners, or essentially exist alongside any closely related taxonomic relatives. The new species was distinct and not just a color-variant within the population based on concordance between the factors of color pattern, mitochondrial DNA, and four nuclear loci.

Three subspecies are recognized as being valid, including the nominotypical subspecies.

• Necturus maculosus louisianensis Viosca, 1937 (Red River mudpuppy)
• Necturus maculosus maculosus (Rafinesque, 1818) (common mudpuppy)
• Necturus maculosus stictus Bishop, 1941 (Lake Winnebago mudpuppy)

Nota bene: A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Necturus.

• Rafinesque CS (1818). "Further Account of Discoveries in Natural History, in the Western States". American Monthly Magazine and Critical Review 4: 39–42. (Sirena maculosa, new species, p. 41).

Media related to Necturus maculosus at Wikimedia Commons

• Mudpuppy (Necturus maculosus), Natural Resources Canada