HOME

TheInfoList



OR:

Plethodontidae, or lungless salamanders, are a family of
salamander Salamanders are a group of amphibians typically characterized by their 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 ten ...
s. Most species are native to the Western Hemisphere, from British Columbia to Brazil, although a few species are found in
Sardinia Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label=Algherese and Catalan) is the second-largest island in the Mediterranean Sea, after ...
, Europe south of the Alps, and South Korea. In terms of number of species, they are by far the largest group of salamanders.


Biology

Adult lungless salamanders have four limbs, with four toes on the fore limbs, and usually with five on the hind limbs. Within many species, mating and reproduction occur solely on land. Accordingly, many species also lack an aquatic larval stage, a phenomenon known as direct development in which the offspring hatch as fully-formed, miniature adults. Direct development is correlated with changes in the developmental characteristics of plethodontids compared to other families of salamanders including increases in egg size and duration of embryonic development. Additionally, the evolutionary loss of the aquatic larval stage is related to a diminishing dependence on aquatic habitats for reproduction. The lift of this constraint allowed widespread colonization and diversification within a broad number of terrestrial habitats which is a testament to the high success and proliferation of Plethodontidae. Many species have a projectile tongue and hyoid apparatus, which they can fire almost a body length at high speed to capture prey. Measured in individual numbers, they are very successful animals where they occur. In some places, they make up the dominant biomass of vertebrates. An estimated 1.88 billion individuals of the southern redback salamander inhabit just one district of
Mark Twain National Forest Mark Twain National Forest (MTNF) is a U.S. United States National Forest, National Forest located in the southern half of Missouri. MTNF was established on September 11, 1939. It is named for author Mark Twain, a Missouri native. The MTNF cover ...
alone, about 1,400 tons of biomass. Due to their modest size and low metabolism, they are able to feed on prey such as
springtails Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ent ...
, which are usually too small for other terrestrial vertebrates. This gives them access to a whole ecological niche with minimal competition from other groups.


Courtship and Mating

Plethodontids exhibit highly stereotyped and complex mating behaviors and courtship rituals that are not present in any other salamander family. Mating behavior tends to be uniform among all plethodontids and typically involves a tail-straddle walk in which the female orients her head at the base of the male's tail while also straddling the tail with her body. The male will twist his body around and deposit a sperm capsule, known as the spermatophore, on the substrate in front of the female's snout. As the male leads the female over the spermatophore with his tail, the female lowers her
cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
onto the spermatophore and lodges the sperm mass inside while leaving the base of the spermatophore on the ground. Within many species of plethodontidae, the courtship ritual is often accompanied by transfer of male
pheromones A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
during the tail-straddling walk. During the breeding period, males will grow enlarged anterior teeth used to scratch the female's skin on her head as a part of the courtship ritual. Subsequently, the male will rub pheromones onto the abraded spot which are secreted from a pad of tissue called the mental gland located underneath the male's chin. Courtship pheromones greatly increase male mating success for a variety of reasons. Overall, the pheromone secretions increase female receptivity to courtship and sperm transfer. This not only increases the likelihood of successful mating with a specific female, but also shortens the duration of courtship which is important because it minimizes the chance of the male being interrupted by other competing males. In scientific literature discussing the variations between the mental glands of plethodontid salamanders, it was discovered that male plethodontids had minor variations in height  and diameter of the simple tubular glands, and major variation was found in the diameter of the secretory granules. This is attributed to the fact that males can mate throughout all months of the year, while females oviposit seasonally.


Respiration

A number of features distinguish the plethodontids from other salamanders. Most significantly, they lack
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
s, conducting respiration through their skin, and the tissues lining their mouths.


Chemoreception

Another distinctive feature is the presence of a vertical slit between the nostril and upper lip, known as the "nasolabial groove". The groove is lined with glands, and enhances the salamander's
chemoreception A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...
which is correlated with a higher degree of olfactory lobe and nasal mucous membrane development in plethodontids. The presence of this specialized structure is likely related to the absence of lungs in these salamanders. Though some lunged salamanders do exhibit similar structures, they are reduced in size and are not arranged near the nostrils (i.e. nares) in the same fashion as plethodontids. Due to the fact that plethodontids cannot generate air pressure via expulsion of air from the lungs and through the nares, they are presented with the challenge of removing water and debris from the nasal passages which has the potential to significantly limit olfactory processes. As such, the nasolabial grooves are structured in a way that maximizes drainage from the nose. The groove is deeper and more narrow directly around the nares and the orifices of the glands are slightly elevated both of which aid in the gravitational flow of fluid from the nares and nasal depression. Additionally, the nasolabial glands around the margins of the nares secrete a fatty film which further encourages the removal of water from the nasal passages due to differences in polarity between water and the lipid secretions.


Evolutionary history

Plethodontidae are estimated to have split from their sister group
Amphiumidae ''Amphiuma'' is a genus of aquatic salamanders from the United States, the only extant genus within the family Amphiumidae . They are colloquially known as amphiumas. They are also known to fishermen as "conger eels" or "Congo snakes", which are ...
around the K-Pg boundary, and to have diversified during the
Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
. The origin region of the family is North America, with oldest of the European members of the family known from the Middle Miocene of Slovakia.


Subfamilies and genera

The family Plethodontidae consists of two extant subfamilies and about 478
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
divided among these genera, making up the majority of known salamander species: Following a major revision in 2006, the genus ''Haideotriton'' was found to be a synonym of '' Eurycea'', while the genus ''Lineatriton'' were made synonyms of ''
Pseudoeurycea ''Pseudoeurycea'' is a genus of salamander in the family Plethodontidae. The members of this genus are commonly known as the false brook salamanders. They are found in Mexico and Guatemala. In order to preserve ''Ixalotriton'' and ''Bolitoglossa ...
''.


Conservation Status

IUCN RedList, (2020). Plethodontidae. Retrieved from https://www.iucnredlist.org/search?taxonomies=101246&searchType=species


References


External links


AmphibiaWeb - Plethodontidae

Tree of Life: Plethodontidae

Caudata Culture Species Database - Plethodontidae
{{Taxonbar, from=Q100340 Salamandroidea Extant Miocene first appearances Amphibian families Taxa named by John Edward Gray