Editing Amphiuma

{{Short description|Genus of amphibians}}
{{Automatic taxobox
| fossil_range = {{fossil range|Paleocene|present}}
| image = Descriptiones et icones amphibiorum (19277946523).jpg
| image_caption = [[Two-toed amphiuma]]
| display_parents = 2
| parent_authority = [[John Edward Gray|Gray]], 1825&nbsp;<ref>{{cite book |author =J. Alan Holman |year=2006 |title=Fossil Salamanders of North America |series=Life of the past |publisher=[[Indiana University Press]] |isbn=978-0-253-34732-9 |page=107 |url=https://books.google.com/books?id=jedqR3axP_MC&pg=PA107}}</ref>
| taxon = Amphiuma
| authority = [[Alexander Garden (naturalist)|Garden]], 1821
| subdivision_ranks = Species
| subdivision = 
''[[Two-toed Amphiuma|Amphiuma means]]''<br />
''[[Amphiuma pholeter]]''<br />
''[[Amphiuma tridactylum]]''
}}

'''''Amphiuma''''' is a [[genus]] of aquatic [[salamander]]s from the United States,<ref name=Frost/> the only [[Extant taxon|extant]] genus within the [[family (biology)|family]] '''Amphiumidae''' {{IPAc-en|æ|m|f|ᵻ|ˈ|juː|m|ᵻ|d|iː}}.<ref name=Frost-Amphiumidae/> They are colloquially known as '''amphiumas'''.<ref name=Frost/> They are also known to fishermen as "[[conger eel]]s" or "Congo snakes", which are [[zoology|zoologically]] incorrect designations or [[misnomer]]s, since amphiumas are actually [[salamander]]s (and thus [[amphibian]]s), and not [[fish]], nor [[reptile]]s and are not from [[Congo Basin|Congo]]. ''Amphiuma'' exhibits one of the largest complements of [[DNA]] in the living world, around 25 times more than a human.<ref>[http://www.scientificblogging.com/genomicron/junk_dna_and_the_onion_test "Junk DNA and the Onion Test"] {{webarchive|url=https://archive.today/20120914055345/http://www.scientificblogging.com/genomicron/junk_dna_and_the_onion_test |date=2012-09-14 }} 1 June 2008.</ref>

== Taxonomy ==
Numerous phylogenetic studies have indicated that amphiumas form a clade with the families [[Torrent salamander|Rhyacotritonidae]] (torrent salamanders) and [[Plethodontidae]] (lungless salamanders), with an especially close relationship to Plethodontidae. Despite this possible relationship, the two families must have still diverged very early on. The genus ''Proamphiuma'' from the Cretaceous is the earliest known member of the family, and closely resembles the modern species aside from less elaborate vertebral structures.<ref>{{cite web|url=http://www.tolweb.org/Amphiumidae|title=Amphiumidae|website=www.tolweb.org|access-date=2018-12-24}}</ref><ref>{{Cite journal|last1=Bonett|first1=Ronald M.|last2=Chippindale|first2=Paul T.|last3=Moler|first3=Paul E.|last4=Van Devender|first4=R. Wayne|last5=Wake|first5=David B.|date=2009-05-20|title=Evolution of Gigantism in Amphiumid Salamanders|journal=PLOS ONE|volume=4|issue=5|pages=e5615|doi=10.1371/journal.pone.0005615|issn=1932-6203|pmc=2680017|pmid=19461997|bibcode=2009PLoSO...4.5615B|doi-access=free}}</ref>

== Description ==
Amphiumas have an elongated body, generally grey-black in color. They do have legs, but they are merely vestigial and very small. While amphiumas can be up to {{convert|116|cm|abbr=on}} long, their legs measure only up to about {{convert|2|cm|abbr=on}}. It is because of this that they are often mistaken for [[eel]]s or snakes. They also lack eyelids and a tongue.<ref name=EoR>{{cite book |editor=Cogger, H.G. |editor2=Zweifel, R.G.|author = Lanza, B.|author2 = Vanni, S.|author3 = Nistri A.|name-list-style = amp|year=1998|title=Encyclopedia of Reptiles and Amphibians|publisher= Academic Press|location=San Diego|page= 72|isbn= 978-0-12-178560-4}}</ref> Amphiumas also have a lateral line visible on the sides of their bodies, which is capable of detecting movement and is used in aid of hunting.{{citation needed|date=August 2022}}

Female amphiumas lay their [[egg (biology)|eggs]] in wet mud, and then remain coiled around them for about five months, until they hatch. The larvae have external gills, but after about four months these external gills disappear and the lungs begin to work. One pair of [[gill slit]]s is retained and never disappears, so the [[metamorphosis (biology)|metamorphosis]] remains incomplete.<ref name=EoR/><ref>[https://books.google.com/books?id=6mczKwsGNAgC&dq=no+urodele+has+internal+gills+Amphiuma+pair+gill+slits&pg=PA174 Amphibian Development]</ref>

=== Species ===
There are three extant amphiuma species,<ref name=Frost/> distinguished by the number of toes:<ref name="Vitt and Caldwell 2014"/>

==== Extant ====
{| class="wikitable"
|-
! Image !! Common Name !! Scientific name !! Distribution
|-
|[[File:Amphiuma tridactylum.jpg|120px]]||[[Amphiuma tridactylum|Three-toed amphiuma]]||''Amphiuma tridactylum''|| Southeastern United States
|-
|[[File:Amphiuma (two-toed).jpg|120px]]||[[Two-toed amphiuma]]||''Amphiuma means''|| Southeastern United States
|-
|[[File:One-toed Amphiuma.jpg|frameless|119x119px]]
|[[Amphiuma pholeter|One-toed amphiuma]]||''Amphiuma pholeter''|| Central Florida, Florida panhandle, extreme southern Georgia, and southern Alabama
|}

==== Extinct ====

* †''[[Amphiuma jepseni]]'' ([[Paleocene]] of [[Wyoming]])
* †''[[Amphiuma antica]]'' ([[Miocene]] of [[Texas]])

== Distribution ==
Amphiumas inhabit the southeastern part of the [[United States]].<ref name=Frost/> They share much of the same distribution with the [[siren (amphibian)|sirens]], although they are not closely related.

In the past, amphiumas had a wider geographic range throughout North America, ranging all the way north to [[Wyoming]].<ref name=fossilworks/>

== Behavior ==
During the day, amphiumas hide in vegetation, and at night they become active hunters. Their prey includes [[frog]]s, [[snake]]s, [[fish]], [[crustacean]]s, [[insect]]s and even other amphiumas. Hunting and eating habits have been observed to be very similar to that of the [[axolotl]], including the sucking in of food by their stomachs with vacuum force. If provoked, they can become aggressive. They can be found in most wetlands in the coastal plain of the southeastern U.S., even ones which periodically dry out, as they are able to [[estivate]] in the moist mud below drained marshland and other [[ephemeral]] wetlands. Amphiumas are rarely encountered on land.

It is the female that courts the male before mating. When a pair is formed they wrap their bodies around each other, and the male will transfer a spermatophore directly into the female cloaca (cloacal apposition).<ref>[https://lucec.loyno.edu/natural-history-writings/amphiuma-or-congo-eel Amphiuma, or Congo Eel]</ref>

=== Food habits ===
The amphiuma's predatory behaviors and food selection are very calculated and variable depending on abundance of food. In addition to eating [[frog]]s, [[snake]]s, [[fish]], [[crustacean]]s, [[insect]]s, and other amphiuma, amphiuma have been found to eat [[annelid]]s, [[vegetable]]s, [[arachnid]]s, [[mollusca]], and [[larva]]e.<ref name="Taylor and Ludlam 2013">{{Cite journal |last1=Taylor |first1=Harrison |last2=Ludlam |first2=John P. |date=2013 |title=The role of size preference in prey selection of ''Amphiuma means'' |journal=BIOS |volume=84 |issue=1 |pages=8–13|doi=10.1893/0005-3155-84.1.8 |jstor=23595338 |s2cid=97908296 }}</ref> Amphiuma seem to have a preference for eating [[crawfish]]. It has been documented that amphiuma will pass on smaller crawfish in order to consume larger ones.<ref>{{Cite journal |last=Chaney |first=Allan H. |date=1951 |title=The food habits of the salamander ''Amphiuma tridactylum'' |jstor=1438050 |journal=Copeia |volume=1951 |issue=1 |pages=45–49 |doi=10.2307/1438050}}</ref> It is suggested that this limits wasting energy in pursuing prey with less caloric density. In captivity, the predatory behavior amphiuma display depends on the presence or lack of food. Amphiuma will remain inactive when food is absent, and will become more active once food has been introduced into their habitat.<ref name="Taylor and Ludlam 2013"/> This shows that the amphiuma, although ancestral to many [[amphibia]], has developed a deductive approach to its predation.{{Citation needed|date=December 2024}}

== Anatomy ==

=== Jaw muscles ===
[[File:Musculature_of_upper_and_lower_Jaw_in_Amphiuma.jpg|thumb|Musculature of upper and lower Jaw in Amphiuma. Specimen from the Pacific Lutheran University Natural History collection, dissection and photos by Misty Lang and Nina Thach]]

Amphiuma are primarily carnivorous amphibians that consume crayfish, insects, and other small invertebrates. Similar to many [[salamander]]s, the amphiuma has two distinct forms of suction feeding procedures: stationary and strike.<ref name=":0">{{Cite thesis |last=Erdman |first=Susan E. |date=1983 |title=Form and function of the feeding apparatus of ''Amphiuma tridactylum'' |url=https://preserve.lehigh.edu/cgi/viewcontent.cgi?article=3330&context=etd |type=MSc thesis |publisher=Lehigh University }}</ref> Stationary suction feeding involve little to no movement where it opens the mouth with buccal expansion but no forward movement of the body.<ref name=":0" /> strike suction is rapid motion where the mouth opens and buccal expansion occurs synchronously leading to a quick attack.<ref name=":0" /> These two feeding habits give the amphiuma the ability to have a larger variety of food (live or dead). amphiuma's ability to displace its jaw to feed means they can consume a large variety of organisms as well. But amphiuma's narrow jaw makes it harder for them to fully consume large prey such as crayfish or mice. In these cases, they will use one of the forms of suction feeding and then rip the prey into pieces until fully consumed.<ref name=":0" /> Small prey will be pulled completely into the mouth before being eaten. Structure of the teeth within the jaw tend to be arched caudal on the head.<ref>{{Cite journal |last=Hilton |first=William |date=1951 |title=Teeth of salamanders |jstor=27669689 |journal=Herpetologica |volume=7 |issue=3 |pages=133–136}}</ref> The muscles of the jaw give them the ability to grab and hold on to prey as well as create a negative pressure to suck in the prey and displace the jaw. Muscles of note in the amphiuma include: the levator mandibulae anterior and levator mandibulae externus, which elevate the lower jaw of the amphiuma while the depressor mandibulae depresses the lower jaw.<ref name=":7">{{Cite book|title=Laboratory Anatomy of Necturus|last=Chiasson|first=Robert|publisher=University of Arizona|year=1973|isbn=978-0-697-04605-5|location=Arizona|pages=14–19}}</ref> The intermandubularis works by tensing the mouth floor. The branchiohyoideus and geniohyoideus draws the hyoid arch which causes the suction and displacement.<ref name=":7" />

=== Lungs ===
Amphiuma possess relatively ancestral forms of lungs compared to some of the other groups of [[salamander]]s that live terrestrially today.<ref name=":33">{{Cite journal |last1=Toews|first1=Daniel P.|last2=McRae|first2=Ann|date=1974|title=Respiratory mechanisms in the aquatic salamander, ''Amphiuma tridactylum'' |jstor=1442591|journal=Copeia|volume=1974|issue=4|pages=917–920|doi=10.2307/1442591}}</ref><ref name=":44">{{Cite journal|last1=Martin|first1=Karen M.|last2=Hutchison|first2=Victor H.|date=1979|title=Ventilatory activity in ''Amphiuma tridactylum'' and ''Siren lacertina'' (Amphibia, Caudata)|jstor=1563477|journal=Journal of Herpetology|volume=13|issue=4|pages=427–434|doi=10.2307/1563477}}</ref> Their lungs are long organs, extending over half of the body length, with dense capillary networks and large surface area that suggest the utilization of the entire lung for respiration while the animal is in water or on land.<ref name=":44"/> Although it is common for amphibia to respire out of their skin, also known as [[cutaneous respiration]], it was found that amphiuma primarily respire through their lungs, despite their aquatic lifestyle.<ref name=":5">{{Cite journal|last=Szarski|first=Henryk|date=1964|title=The structure of respiratory organs in relation to body size in Amphibia |jstor=2406426|journal=Evolution|volume=18|issue=1|pages=118–126|doi=10.2307/2406426}}</ref> This is suggested by the high lung to respiratory capillary density compared to the relatively low skin to respiratory capillary density.<ref name=":44"/><ref name=":5" />
[[File:Zoomed in and Annotated Amphiuma Lung with Body Orientation.jpg|thumb|Amphiuma lung with a magnified portion of the lung to show the amphiuma vascular tissue.]]

==== Respiration ====
Pressure gradients for respiration occur in two different locations, the buccal cavity/nares (mouth and nostril) region, and in the lungs of the amphiuma. The first system for respiration occurs in the buccal cavity/nares through a two-cycle pressure-induced buccal cavity/nares process.<ref name=":33"/><ref name=":62">{{Cite journal |last1=Brainerd |first1=Elizabeth |last2=Ditelberg |first2=Jeremy |date=1993 |title=Lung ventilation in salamanders and the evolution of vertebrate air-breathing mechanisms |doi=10.1006/bijl.1993.1028 |journal=Biological Journal of the Linnean Society|volume=49|issue=2 |pages=163–183|doi-access= }}</ref><ref name=":44"/> In the first system, the amphiuma performs one full cycle of body expansion and compression in order to inhale and another full cycle to exhale, a unique process that utilizes both the [[Mouth|buccal cavity]] and the nares (openings of nostrils).<ref name=":33" /><ref name=":62" /> The buccal cavity creates pressure that aids in driving the cycles of expansion and compression required for respiration, although it was found that the buccal pressure gradient alone was not enough to drive respiration in the ''[[Amphiuma tridactylum]]''.<ref name=":33" /> Rather, the buccal cavity allows for small pressure changes that are thought to have an [[Olfaction|olfactory]] purpose.<ref name=":33" />  This buccal cavity/nares component to the amphiuma respiratory process supplements the contribution performed by the lung. It is the pressure control performed in the lungs that drive the inhalation and exhalation forces through the flexing of [[Smooth muscle tissue|smooth muscle]] in the lung.<ref name=":44" /> In order to exhale, amphiuma push air from their lungs into their buccal cavity, distending the cavity, before releasing the air. Without inhaling, amphiuma repeat the process, exhaling a second volume of air that allows them to completely empty their lungs.<ref name=":44" /> Only after both exhales can they then inhale, using a negative pressure gradient made by the smooth muscles in their lungs to take in air.<ref name=":44" /> [[File:Amphiumadig.jpg|thumb|Amphiuma digestive tract. Specimen from the Pacific Lutheran University Natural History collection, dissection and photos by Misty Lang and Nina Thach.]]

== Sexual dimorphism ==
Amphiuma demonstrate [[sexual dimorphism]] in relation to the size of their bodies and the size of their heads.<ref name=":1">{{Cite journal|last1=Fontenot|first1=Clifford L.|last2=Seigel|first2=Richard A.|title=Sexual dimorphism in the three-toed amphiuma, ''Amphiuma tridactylum'': sexual selection or ecological causes |journal=Copeia|language=en-US|volume=2008|issue=1|pages=39–42|doi=10.1643/cg-06-060|year=2008|s2cid=30731154}}</ref> Generally, males have been found to possess larger bodies and longer heads compared to the female sex, which normally is indicative of male-male combat observed within the population.<ref name=":1" /><ref name=":2">{{Cite journal|last=Shine|first=Richard|date=1979|title=Sexual selection and sexual dimorphism in the Amphibia |jstor=1443418|journal=Copeia|volume=1979|issue=2|pages=297–306|doi=10.2307/1443418}}</ref> There has been, however, no other physical indicating factors for male-male combat as in other species of amphibians, such as horns or spines.<ref name=":2" /> Some populations do not show these sexual dimorphic traits, and in certain locations female and male bodies do not exhibit any traits with significant differences.<ref name=":02">{{Cite journal|last=Cagle|first=Fred R.|date=1948|title=Observations on a population of the salamander, ''Amphiuma tridactylum'' Cuvier |jstor=1932640|journal=Ecology|volume=29|issue=4|pages=479–491|doi=10.2307/1932640}}</ref>

Amphiumas may be sexed as male or female based on the pigmentation of the cloacal opening.<ref name=":4">{{Cite journal|last=Fontenot|first=Clifford L.|title=Reproductive Biology of the Aquatic Salamander Amphiuma Tridactylum in Louisiana|journal=Journal of Herpetology|language=en-US|volume=33|issue=1|pages=100–105|doi=10.2307/1565548|year=1999|jstor=1565548}}</ref> Males exhibit white or pink coloration while females exhibit dark pigmentation. Occasionally, males may demonstrate partial pigmentation, but never have full dark coloration like that of females.

==References==
{{Reflist|30em|refs=
<ref name=fossilworks>{{cite web |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=37367 |title=''Amphiuma'' Garden 1821 |work=Paleobiology Database |publisher=Fossilworks |access-date=17 December 2021}}</ref>

<ref name=Frost>{{cite web |url=http://research.amnh.org/vz/herpetology/amphibia/Amphibia/Caudata/Amphiumidae/Amphiuma |title=''Amphiuma'' Garden, 1821 |author=Frost, Darrel R. |year=2018 |work=Amphibian Species of the World: an Online Reference. Version 6.0 |publisher=American Museum of Natural History |access-date=11 September 2018}}</ref>

<ref name=Frost-Amphiumidae>{{cite web |url=http://research.amnh.org/vz/herpetology/amphibia/Amphibia/Caudata/Amphiumidae |title=Amphiumidae Gray, 1825 |author=Frost, Darrel R. |year=2018 |work=Amphibian Species of the World: an Online Reference. Version 6.0 |publisher=American Museum of Natural History |access-date=11 September 2018}}</ref>

<ref name="Vitt and Caldwell 2014">{{cite book|title=Herpetology: An Introductory Biology of Amphibians and Reptiles |edition=4th |first1=Laurie J. |last1=Vitt |first2=Janalee P. |last2=Caldwell |name-list-style=amp |publisher=Academic Press |year=2014 |page=466}}</ref>
}}

==External links==
* {{Wikispecies-inline|Amphiuma|''Amphiuma''}}
* [http://tolweb.org/Amphiumidae/15440 Tree of Life: Amphiumidae]
*[http://www.amphiumas.org amphiumas.org]

{{Caudata}}
{{Taxonbar|from=Q300923}}
{{Authority control}}

[[Category:Salamandroidea]]
[[Category:Extant Pleistocene first appearances]]
[[Category:Amphibian genera]]
[[Category:Endemic amphibians of the United States]]
[[Category:Taxa named by Alexander Garden (naturalist)]]