Salamanders are a group of amphibians typically characterized by a lizard-like
appearance, with slender bodies, blunt snouts, short limbs projecting at right
angles to the body, and the presence of a tail in both larvae and adults. All
present-day salamander families are grouped together under the scientific
name Urodela. Salamander diversity is most abundant in the Northern
Hemisphere and most species are found in the Holarctic ecozone, with some species present in the Neotropical zone.
Salamanders never have more than four toes on their front
legs and five on their rear legs, but some species have fewer digits and others
lack hind limbs. Their permeable skin usually makes them reliant on habitats in
or near water or other cool, damp places. Some salamander species are fully
aquatic throughout their lives, some take to the water intermittently, and
others are entirely terrestrial as adults. Unique among vertebrates, they are capable of regenerating lost limbs, as well as other damaged parts of their
bodies. Researchers hope to reverse engineer the remarkable regenerative
processes for potential human medical applications, such as brain and spinal
cord injury treatment or preventing harmful scarring during heart surgery
recovery. Members of the family Salamandridae are mostly known as newts and
lack the costal
grooves along the sides of their bodies
typical of other groups. The skin of some species contains the powerful
poison tetrodotoxin; these salamanders tend to be slow-moving and have
bright warning
coloration to advertise their toxicity.
Salamanders typically lay eggs in water and have aquatic larvae, but great
variation occurs in their lifecycles. Some species in harsh environments reproduce while
still in the larval state.
In literature and legend, the salamander is associated
with fire, being supposedly unharmed by the flames, while clothes made from its
skins or 'wool' were believed to be incombustible. More plausibly, salamanders
were said to be intensely poisonous. Despite this, salamander brandy, a drink
prepared by dunking live salamanders in fermenting fruit juices, is reputed to
have hallucinogenic and aphrodisiac properties.
The skin lacks scales and is moist and smooth to the
touch, except in newts of the Salamandridae, which may have velvety or
warty skin, wet to the touch. The skin may be drab or brightly colored,
exhibiting various patterns of stripes, bars, spots, blotches, or dots. Male
newts become dramatically colored during the breeding season. Cave species
dwelling in darkness lack pigmentation and have a translucent pink or
pearlescent appearance.
Salamanders range in size from the minute salamanders, with a total length of 2.7 cm (1.1 in),
including the tail, to the Chinese giant
salamander which reaches 1.8 m
(5.9 ft) and weighs up to 65 kg (143 lb). Most, however, are
between 10 and 20 cm (3.9 and 7.9 in) in length.
Trunk, limbs and tail
An adult salamander generally resembles a small lizard,
having a basal tetrapod body form with a cylindrical trunk, four limbs, and
a long tail. Except in the family Salamandridae, the head, body, and tail have
a number of vertical depressions in the surface which run from the mid-dorsal
region to the ventral area and are known as costal grooves. Their function seems to be to help keep the skin moist
by channeling water over the surface of the body.
Some aquatic species, such as sirens and amphiumas, have reduced or absent hind limbs, giving them an eel-like
appearance, but in most species, the front and rear limbs are about the same
length and project sidewards, barely raising the trunk off the ground. The feet
are broad with short digits, usually four on the front feet and five on the
rear. Salamanders do not have claws, and the shape of the foot varies according
to the animal's habitat. Climbing species have elongated, square-tipped toes,
while rock-dwellers have larger feet with short, blunt toes. The tree-climbing salamander (Bolitoglossa sp.) has plate-like webbed feet which adhere to
smooth surfaces by suction, while the rock-climbing Hydromantes species from California have feet with fleshy webs
and short digits and use their tails as an extra limb. When ascending, the tail
props up the rear of the body, while one hind foot moves forward and then
swings to the other side to provide support as the other hind foot advances.
In larvae and aquatic salamanders, the tail is laterally
flattened, has dorsal and ventral fins, and undulates from side to side to
propel the animal through the water. In the families Ambystomatidae and Salamandridae, the male's tail, which is larger
than that of the female, is used during the amplexus embrace to propel the mating couple to a secluded location.
In terrestrial species, the tail moves to counterbalance the animal as it runs,
while in the arboreal salamander and other tree-climbing species, it is prehensile. The tail is also used by certain plethodontid
salamanders that can jump, to help launch
themselves into the air. The tail is used in courtship and as a storage organ for proteins and lipids. It
also functions as a defense against predation, when it may be lashed at the
attacker or autotomised when grabbed. Unlike frogs, an adult salamander is
able to regenerate limbs and its tail when these are lost.
Skin
The skin of salamanders, in common with other amphibians,
is thin, permeable to water, serves as a respiratory membrane, and is
well-supplied with glands. It has highly cornified outer layers, renewed periodically through a skin shedding process controlled by hormones from the pituitary and thyroid glands. During moulting, the skin initially breaks around the
mouth, and the animal moves forwards through the gap to shed the skin. When the
front limbs have been worked clear, a series of body ripples pushes the skin
towards the rear. The hind limbs are extracted and push the skin farther back,
before it is eventually freed by friction as the salamander moves forward with
the tail pressed against the ground. The animal often then eats the
resulting sloughed skin.
Glands in the skin discharge mucus which
keeps the skin moist, an important factor in skin respiration and
thermoregulation. The sticky layer helps protect against bacterial infections
and molds, reduces friction when swimming, and makes the animal slippery and
more difficult for predators to catch. Granular glands scattered on the upper
surface, particularly the head, back, and tail, produce repellent or toxic
secretions. Some salamander toxins are particularly potent. The rough-skinned newt (Taricha
granulosa) produces the neurotoxin tetrodotoxin, the most toxic nonprotein substance known. Handling the
newts does no harm, but ingestion of even a minute fragment of skin is deadly.
In feeding trials, fish, frogs, reptiles, birds, and mammals were all found to
be susceptible.
Mature adults of some salamander species have
"nuptial" glandular tissue in their cloacae, at the base of their
tails, on their heads or under their chins. Some females release chemical substances, possibly from the ventral cloacal gland, to attract
males, but males do not seem to use pheromones for this purpose.[9] In
some plethodonts, males have conspicuous mental glands on the chin which
are pressed against the females' nostrils during the courtship ritual. They may
function to speed up the mating process, reducing the risk of its being
disrupted by a predator or rival male. The gland at the base of the tail
in Plethodon cinereusis
used to mark fecal
pellets to proclaim territorial ownership.
Senses
Olfaction in salamanders plays a role in territory
maintenance, the recognition of predators, and courtship rituals, but is
probably secondary to sight during prey selection and feeding. Salamanders have
two types of sensory areas that respond to the chemistry of the environment.
Olfactory epithelium in the nasal cavity picks up airborne and aquatic odors,
while adjoining vomeronasal organs detect nonvolatile chemical cues, such as tastes in
the mouth. In plethodonts, the sensory epithelium of the vomeronasal organs
extends to the nasolabial grooves, which stretch from the nostrils to the corners of the
mouth. These extended areas seem to be associated with the identification of
prey items, the recognition of conspecifics, and the identification of individuals.
The eyes of most salamanders are adapted primarily for
vision at night. In some permanently aquatic species, they are reduced in size
and have a simplified retinal structure, and in cave dwellers such as the Georgia blind
salamander, they are absent or covered with a
layer of skin. In amphibious species, the eyes are a compromise and are nearsighted in air and farsighted in water. Fully terrestrial species such as
the fire
salamander have a flatter lens which can
focus over a much wider range of distances. To find their prey,
salamanders use trichromatic color vision extending into the ultraviolet range, based on three photoreceptor types that are maximally sensitive around 450, 500,
and 570 nm. The larvae, and the adults of some highly aquatic
species, also have a lateral line organ, similar to that of fish, which can detect
changes in water pressure.
All salamanders lack middle ear cavity, eardrum and eustachian tube, but have an opercularis system like frogs, and are
still able to detect airborne sound. The opercularis system consists of
two ossicles: the columella (equivalent to the stapes of higher vertebrates) which is fused to the skull, and the operculum. An
opercularis muscle connects the latter to the pectoral girdle, and is kept
under tension when the animal is alert. The system seems able to detect
low-frequency vibrations (500–600 Hz), which may be picked up from the
ground by the fore limbs and transmitted to the inner ear. These may serve to
warn the animal of an approaching predator.
Salamanders are usually considered to have no voice and
do not use sound for communication in the way that frogs do; however, some
species can make quiet ticking or popping noises, perhaps by the opening and
closing of valves in the nose. The California
giant salamander can produce a bark or
rattle, and a few species can squeak by contracting muscles in the throat. The
arboreal salamander can squeak using a different mechanism; it retracts its
eyes into its head, forcing air out of its mouth. The ensatina salamander occasionally makes a hissing sound, while the sirens sometimes produce quiet clicks, and can resort to
faint shrieks if attacked. Vocalization in salamanders has been little studied
and the purpose of these sounds is presumed to be the startling of predators.
Respiration
Respiration differs among the different species of salamanders,
and can involve gills, lungs, skin, and the membranes of mouth and throat.
Larval salamanders breathe primarily by means of gills,
which are usually external and feathery in appearance. Water is drawn in
through the mouth and flows out through the gill slits. Some neotenic species such as the mudpuppy (Necturus
maculosus) retain their gills throughout
their lives, but most species lose them at metamorphosis. The embryos of
some terrestrial lungless salamanders, such as Ensatina,
that undergo direct development, have large gills that lie close to the egg's
surface.
When present in adult salamanders, lungs vary greatly
among different species in size and structure. In aquatic, cold-water species
like the southern
torrent salamander (Rhyacotriton variegatus), the lungs are very small with smooth walls, while
species living in warm water with little dissolved oxygen, such as the lesser siren (Siren
intermedia), have large lungs with
convoluted surfaces. In the terrestrial lungless salamanders (family Plethodontidae), no lungs or gills are present,
and gas
exchange mostly takes place through the
skin, supplemented by the tissues lining the mouth. To facilitate this, these
salamanders have a dense network of blood vessels just under the skin and in
the mouth.
In the Amphiumas, metamorphosis is
incomplete, and they retain one pair of gill slits as adults, with fully functioning internal
gills. Some species that lack lungs respire through gills. In most cases,
these are external gills, visible as tufts on either side of the head. Some
terrestrial salamanders have lungs used in respiration, although these are
simple and sac-like, unlike the more complex organs found in mammals.
Many species, such as the olm,
have both lungs and gills as adults.
In the Necturus, external gills
begin to form as a means of combating hypoxia in the egg as egg yolk is
converted into metabolically active tissue. However, molecular changes in the
mudpuppy during post-embryonic development primarily due to the thyroid gland prevent the internalization of the external gills
as seen in most salamanders that undergo metamorphosis. The external gills seen
in salamanders differs greatly from that of amphibians with internalized gills.
Unlike amphibians with internalized gills which typically rely on the changing
of pressures within the buccal and pharyngeal cavities to ensure diffusion of
oxygen onto the gill curtain, neotenic salamanders such as Necturus use
specified musculature, such as the levatores arcuum, to move external gills to
keep the respiratory surfaces constantly in contact with new oxygenated water.
Feeding and diet
Salamanders are opportunistic predators. They are generally not restricted to specific foods,
but feed on almost any organism of a reasonable size. Large species such
as the Japanese giant
salamander (Andrias japonicus) eat
crabs, fish, small mammals, amphibians, and aquatic insects. In a study of
smaller dusky
salamanders (Desmognathus) in the Appalachian
Mountains, their diet includes earthworms, flies, beetles, beetle larvae, leafhoppers, springtails, moths, spiders, grasshoppers, and mites. Cannibalism sometimes takes place, especially when resources
are short or time is limited. Tiger salamander tadpoles in ephemeral pools
sometimes resort to eating each other, and are seemingly able to target
unrelated individuals. Adult blackbelly
salamanders (Desmognathus quadramaculatus) prey on adults and young of other species of
salamanders, while their larvae sometimes cannibalise smaller larvae.
Most species of salamander have small teeth in both their
upper and lower jaws. Unlike frogs,
even the larvae of salamanders possess these teeth. Although larval teeth
are shaped like pointed cones, the teeth of adults are adapted to enable them
to readily grasp prey. The crown, which has two cusps (bicuspid), is attached to a
pedicel by collagenous fibers. The joint formed between the bicuspid and
the pedicel is partially flexible, as it can bend inward, but not outward. When
struggling prey is advanced into the salamander's mouth, the teeth tips relax
and bend in the same direction, encouraging movement toward the throat, and
resisting the prey's escape. Many salamanders have patches of teeth
attached to the vomer and the palatine bones in the roof of the mouth, and these help to retain
prey. All types of teeth are resorbed and replaced at intervals throughout the
animal's life.
A terrestrial salamander catches its prey by flicking out
its sticky tongue in an action that takes less than half a second. In
some species, the tongue is attached anteriorly to the floor of the mouth,
while in others, it is mounted on a pedicel. It is rendered sticky by
secretions of mucus from glands in its tip and on the roof of the
mouth. High-speed cinematography shows how the tiger salamander (Ambystoma
tigrinum) positions itself with its snout
close to its prey. Its mouth then gapes widely, the lower jaw remains
stationary, and the tongue bulges and changes shape as it shoots forward. The
protruded tongue has a central depression, and the rim of this collapses inward
as the target is struck, trapping the prey in a mucus-laden trough. Here it is
held while the animal's neck is flexed, the tongue retracted and jaws closed.
Large or resistant prey is retained by the teeth while repeated protrusions and
retractions of the tongue draw it in. Swallowing involves alternate contraction
and relaxation of muscles in the throat, assisted by depression of the eyeballs
into the roof of the mouth. Many lungless salamanders of the family
Plethodontidae have more elaborate feeding methods. Muscles surrounding
the hyoid bone contract to store elastic energy in springy
connective tissue, and actually "shoot" the hyoid bone out of the
mouth, thus elongating the tongue. Muscles that originate in the pelvic
region and insert in the tongue are used to reel the tongue and the hyoid back
to their original positions.
An
aquatic salamander lacks muscles in the tongue, and captures its prey in an
entirely different manner. It grabs the food item, grasps it with its teeth,
and adopts a kind of inertial feeding. This involves tossing its head about,
drawing water sharply in and out of its mouth, and snapping its jaws, all of
which tend to tear and macerate the prey, which is then swallowed.
Though frequently feeding on slow-moving animals
like snails, shrimps and worms, sirenids are unique among salamanders for having developed
speciations towards herbivory, such as beak-like jaw ends and extensive
intestines. They feed on algae and other soft-plants in the wild, and easily
eat offered lettuce.
Defense
Salamanders
have thin skins and soft bodies, and move rather slowly, and at first sight
might appear to be vulnerable to opportunistic predation. However, they have
several effective lines of defense. Mucus coating on damp skin makes them
difficult to grasp, and the slimy coating may have an offensive taste or be
toxic. When attacked by a predator, a salamander may position itself to make
the main poison glands face the aggressor. Often, these are on the tail, which
may be waggled or turned up and arched over the animal's back. The sacrifice of
the tail may be a worthwhile strategy, if the salamander escapes with its life
and the predator learns to avoid that species of salamander in future.
Aposematism
Skin
secretions of the tiger salamander (Ambystoma
tigrinum) fed to rats have been shown to produce aversion to the flavor,
and the rats avoided the presentational medium when it was offered to them
again. The fire salamander (Salamandra
salamandra) has a ridge of large granular glands down its spine which
are able to squirt a fine jet of toxic fluid at its attacker. By angling its
body appropriately, it can accurately direct the spray for a distance of up to
80 cm (31 in).
The Iberian ribbed newt (Pleurodeles
waltl) has another method of deterring
aggressors. Its skin exudes a poisonous, viscous fluid and at the same time,
the newt rotates its sharply pointed ribs through an angle between 27 and 92°,
and adopts an inflated posture. This action causes the ribs to puncture the
body wall, each rib protruding through an orange wart arranged in a lateral
row. This may provide an aposematicsignal that makes the spines more visible. When the
danger has passed, the ribs retract and the skin heals.
Camouflage and mimicry
Although many salamanders have cryptic colors so as to be unnoticeable, others signal their toxicity by their vivid coloring. Yellow, orange, and red are the colors generally used,
often with black for greater contrast. Sometimes, the animal postures if
attacked, revealing a flash of warning hue on its underside. The red eft, the
brightly colored terrestrial juvenile form of the eastern newt (Notophthalmus
viridescens), is highly poisonous. It is
avoided by birds and snakes, and can survive for up to 30 minutes after being
swallowed (later being regurgitated). The red salamander (Pseudotriton
ruber) is a palatable species with a similar
coloring to the red eft. Predators that previously fed on it have been shown to
avoid it after encountering red efts, an example of Batesian mimicry. Other species exhibit similar mimicry. In
California, the palatable yellow-eyed salamander (Ensatina eschscholtzii) closely resembles the toxic California newt (Taricha
torosa) and the rough-skinned newt (Taricha granulosa), whereas in other parts of its range, it is cryptically
colored. A correlation exists between the toxicity of Californian
salamander species and diurnal habits: relatively harmless species like the California
slender salamander (Batrachoseps attenuatus) are nocturnal and are eaten by snakes, while the California newt
has many large poison glands in its skin, is diurnal, and is avoided by snakes.
Autotomy
Some salamander species use tail autotomy to escape
predators. The tail drops off and wriggles around for a while after an attack,
and the salamander either runs away or stays still enough not to be noticed
while the predator is distracted. The tail regrows with time, and salamanders
routinely regenerate other complex tissues, including the lens or retina of
the eye. Within only a few weeks of losing a piece of a limb, a salamander
perfectly reforms the missing structure.
Distribution and habitat
Salamanders split off from the other amphibians during
the mid- to late Permian, and initially were similar to modern members of
the Cryptobranchoidea. Their resemblance to lizardsis
the result of symplesiomorphy, their common retention of the primitive tetrapod body
plan, and they are no more closely related to lizards than they are to mammals.
Their nearest relatives are the frogs and toads, within Batrachia. The earliest known salamander fossils have been found
in geological deposits in China and Kazakhstan, dated to the middle Jurassic period around 164 million years ago.
Salamanders are found only in the Holarctic and Neotropical regions, not reaching south of the Mediterranean Basin, the Himalayas, or in South America the Amazon Basin. They do not extend north of the Arctic tree line, with the northernmost Asian species, Salamandrella keyserlingii occurring in the Siberian larch forests of Sakha and the most northerly species in North
America, Ambystoma laterale,
reaching no farther north than Labrador and Taricha granulosa not
beyond the Alaska
Panhandle. They had an exclusively Laurasian distribution until Bolitoglossa invaded South America from Central America,
probably by the start of the Early Miocene, about 23 million years ago. They also lived on
the Caribbean
Islands during the early Miocene epoch, confirmed by the discovery of Palaeoplethodon hispaniolae[49], found trapped in amber in
the Dominican
Republic. However, possible salamander fossils
have been found on the Australian sites of Riversleigh and Murgon.
There are about 655 living species of
salamander. One-third of the known salamander species are found in North
America. The highest concentration of these is found in the Appalachian
Mountains region, where the Plethodontidae are thought to have originated in
mountain streams. Here, vegetation zones and proximity to water are of greater
importance than altitude. Only species that adopted a more terrestrial mode of
life have been able to disperse to other localities. The northern slimy
salamander (Plethodon glutinosus)
has a wide range and occupies a habitat similar to that of the southern
gray-cheeked salamander (Plethodon metcalfi). The latter is restricted to the slightly cooler and
wetter conditions in north-facing cove forests in the southern Appalachians, and to higher
elevations above 900 m (3,000 ft), while the former is more adaptable, and
would be perfectly able to inhabit these locations, but some unknown factor
seems to prevent the two species from co-existing.
Reproduction and development
Salamanders are not vocal and in most species the sexes
look alike, so they use olfactory and tactile cues to identify potential mates,
and sexual
selection does occur. Pheromones play an
important part in the process and may be produced by the abdominal gland in
males and by the cloacal glands and skin in both sexes. Males are sometimes to
be seen investigating potential mates with their snouts. In Old World
newts, Triturus spp.,
the males are sexually dimorphic and display in front of the females. Visual cues
are also thought to be important in some Plethodont species.
In about 90% of all species, fertilisation is internal.
The male typically deposits a spermatophore on the ground or in the water according to species,
and the female picks this up with her vent. The spermatophore has a packet of
sperm supported on a conical gelatinous base, and often an elaborate courtship
behavior is involved in its deposition and collection. Once inside the cloaca,
the spermatozoa move to the spermatheca, one or more chambers in the roof of the cloaca, where
they are
stored for sometimes lengthy periods until
the eggs are laid. In the most primitive salamanders, such as the Asiatic salamanders and the giant salamanders, external fertilization occurs, instead. In these
species, the male releases sperm onto the egg mass in a reproductive process
similar to that of typical frogs.
Three different types of egg deposition occur. Ambystoma and Taricha spp. spawn large numbers of small eggs in quiet
ponds where many large predators are unlikely. Most dusky salamanders (Desmognathus) and Pacific giant
salamanders (Dicamptodon) lay smaller batches of medium-sized eggs in a concealed
site in flowing water, and these are usually guarded by an adult, normally the
female. Many of the tropical climbing salamanders (Bolitoglossa) and lungless salamanders (Plethodontinae) lay a small
number of large eggs on land in a well-hidden spot, where they are also guarded
by the mother. Some species such as the fire salamanders (Salamandra) are ovoviviparous, with the female retaining the eggs inside her body
until they hatch, either into larvae to be deposited in a water body, or into
fully formed juveniles.
In temperate regions, reproduction is usually seasonal
and salamanders may migrate to breeding grounds. Males usually arrive first and
in some instances set up territories. Typically, a larval stage follows in which the organism
is fully aquatic. The tadpole has three pairs of external gills, no eyelids, a
long body, a laterally flattened tail with dorsal and ventral fins and in some
species limb-buds or limbs. Pond-type larvae may have a pair of rod-like
balancers on either side of the head, long gill filaments and broad fins.
Stream-type larvae are more slender with short gill filaments, narrower fins
and no balancers, but instead have hind limbs already developed when they
hatch. The tadpoles are carnivorous and the larval stage may last from days to years,
depending on species. Sometimes this stage is completely bypassed, and the eggs
of most lungless salamanders (Plethodontidae) develop directly into miniature
versions of the adult without an intervening larval stage.
By the end of the larval stage, the tadpoles already have
limbs and metamorphosis takes place normally. In salamanders, this occurs
over a short period of time and involves the closing of the gill slits and the
loss of structures such as gills and tail fins that are not required as adults.
At the same time, eyelids develop, the mouth becomes wider, a tongue appears,
and teeth are formed. The aqueous larva emerges onto land as a terrestrial
adult.
Not all species of salamanders follow this path. Neoteny, also known as paedomorphosis, has been observed in all salamander
families, and may be universally possible in all salamander species. In this
state, an individual may retain gills or other juvenile features while
attaining reproductive maturity. The changes that take place at metamorphosis
are under the control of thyroid hormones and in obligate neotenes such as the axolotl (Ambystoma
mexicanum), the tissues are seemingly
unresponsive to the hormones. In other species, the changes may not be
triggered because of underactivity of the hypothalamus-pituitary-thyroid
mechanism which may occur when conditions in the terrestrial environment are
too inhospitable. This may be due to cold or wildly fluctuating
temperatures, aridity, lack of food, lack of cover, or insufficient iodine for
the formation of thyroid hormones. Genetics may also play a part. The larvae of
tiger salamanders (Ambystoma
tigrinum), for example, develop limbs soon
after hatching and in seasonal pools promptly undergo metamorphosis. Other
larvae, especially in permanent pools and warmer climates, may not undergo
metamorphosis until fully adult in size. Other populations in colder climates
may not metamorphose at all, and become sexually mature while in their larval
forms. Neoteny allows the species to survive even when the terrestrial
environment is too harsh for the adults to thrive on land.
Conservation
A general decline in living amphibian species has been
linked with the fungal disease chytridiomycosis. A higher proportion of salamander species than of frogs
or caecilians are in one of the at-risk categories established by the IUCN.
Salamanders showed a significant diminution in numbers in the last few decades
of the 20th century, although no direct link between the fungus and the
population decline has yet been found. The IUCN made further efforts in
2005 as they established the Amphibian Conservation Action Plan (ACAP), which
was subsequently followed by Amphibian Ark (AArk), Amphibian Specialist Group
(ASG), and finally the umbrella organization known as the Amphibian Survival
Alliance (ASA). Researchers also cite deforestation, resulting in fragmentation of suitable habitats,
and climate
change as possible contributory factors.
Species such as Pseudoeurycea brunnata and Pseudoeurycea goebeli that had been abundant in the cloud forests of Guatemala and Mexico during the 1970s were found
by 2009 to be rare. However, few data have been gathered on population
sizes over the years, and by intensive surveying of historic and suitable new
locations, it has been possible to locate individuals of other species such
as Parvimolge townsendi, which had been thought to be extinct. Currently, the major lines of defense for the
conservation of Salamanders includes both in situ and ex situ conservation methods.There are efforts in place for
certain members of the Salamander family to be conserved under a conservation
breeding program (CBP) but it is important to note that there should be
research done ahead of time to determine if the Salamander species is actually
going to value from the CBP, as researchers have noted that some species of
amphibians completely fail in this environment.
Various conservation initiatives are being attempted
around the world. The Chinese giant
salamander, at 1.8 m (6 ft) the
largest amphibian in the world, is critically
endangered, as it is collected for food and for
use in traditional
Chinese medicine. An environmental education
programme is being undertaken to encourage sustainable management of wild
populations in the Qinling Mountains and captive breeding programmes have been set
up. The hellbender is another large, long-lived species with dwindling
numbers and fewer juveniles reaching maturity than previously. Another
alarming finding is the increase in abnormalities in up to 90% of the
hellbender population in the Spring River watershed in Arkansas. Habitat loss, silting
of streams, pollution and disease have all been implicated in the decline and a
captive breeding programme at Saint Louis Zoo has been successfully established. Of the 20
species of minute salamanders (Thorius spp.) in Mexico,
half are believed to have become extinct and most of the others are critically
endangered. Specific reasons for the decline may include climate change,
chytridiomycosis, or volcanic activity, but the main threat is habitat destruction
as logging, agricultural activities, and human settlement reduce their often
tiny, fragmented ranges. Survey work is being undertaken to assess the status
of these salamanders, and to better understand the factors involved in their
population declines, with a view to taking action.
Ambystoma mexicanum, an aquatic salamander, is a species protected under the
Mexican UMA (Unit for Management and conservation of wildlife) as of April
1994. However, there are a number of factors that work against their
preservation and conservation methods. The most profound factors are that the
waters in which they are endemic are severely polluted and that even if they
were found in the wild again they would be fished up for either research or
exotic animal sells on the black market. Another detrimental factor is
that the axolotl lost their role as a top predator since the introduction of
locally exotic species such as Nile tilapia and carp. Tilapia and carp directly
compete with axolotls by consuming their eggs, larvae, and juveniles. Climate
change has also immensely affected axolotls and their populations throughout
the southern Mexico area. Due to its proximity to Mexico City, officials are
currently working on programs at Lake Xochimilco to bring in tourism and
educate the local population on the restoration of the natural habitat of these
creatures. This proximity is a large factor that has impacted the survival
of the axolotl, as the city has expanded to take over the Xochimilco region in
order to make use of its resources for water and provision and
sewage. However, the axolotl has the benefit of being raised in farms for
the purpose of research facilities. So there is still a chance that they may be
able to return to their natural habitat. The recent decline in population has
substantially impacted genetic diversity among populations of axolotl, making
it difficult to further progress scientifically. It is important to note that
although there is a level of limited genetic diversity due
to Ambystoma populations, such as the axolotl, being paedeomorphic
species, it does not account for the overall lack of diversity. There is
evidence that points towards a historical bottlenecking
of Ambystoma that contributes to the variation issues. Unfortunately,
there is no large genetic pool for the species to pull from unlike in
historical times.Thus there is severe concern for inbreeding due to lack of
gene flow. One way researchers are looking into maintaining genetic
diversity within the population is via cryopreservation of the spermatophores
from the male axolotl. It is a safe and non-invasive method that requires the
collection of the spermatophores and places them into a deep freeze for
preservation. Most importantly, they have found that there in only limited
damage done to the spermatophores upon thawing and thus it is a viable option.
As of 2013, it is a method that is being used to save not only the axolotl but
also numerous other members of the salamander family.
Research is being done on the environmental cues that
have to be replicated before captive animals can be persuaded to breed. Common
species such as the tiger salamander and the mudpuppy are being given hormones
to stimulate the production of sperm and eggs, and the role of arginine vasotocin in courtship behaviour is being investigated.
Another line of research is artificial
insemination, either in
vitro or by inserting
spermatophores into the cloacae of females. The results of this research may be
used in captive-breeding programmes for endangered species.