25.
Townsend's Dwarf Salamander
(Parvimolge townsendi)
EN
Overview
Townsend’s dwarf salamander is the solitary representative of its genus, and its lineage may have diverged from all other amphibian species over 34 million years ago at a time when monkeys and humans shared a common ancestor. This species inhabits cloud forest and oak forest, and is found living in bromeliads. It can survive in shaded coffee plantations, providing that humidity is retained, but is not found in heavily disturbed areas. Its habitat is being lost due to expanding agriculture and human settlements, as well as the extraction of wood.
Urgent Conservation Actions
Further survey work; protection and restoration of remaining habitat; encouragement of ecologically sensitive land uses, such as shade coffee cultivation.
Distribution
East-central Veracruz, Mexico
Evolutionary Distinctiveness
Order: Caudata
Family: Plethodontidae
The Plethodontidae is by far the largest family of salamanders, comprising nearly 70% of all living species. In total there are 378 known plethodontids divided between four subfamilies and 24 genera. The plethodontids are united by the fact that they do not possess lungs and breathe entirely through their skin and mouth lining. They are often referred to as the lungless salamanders, although they are thought to have evolved from highly aquatic, lunged ancestors in the streams of the Appalachian Mountains in eastern North America. The earliest plethodontids were hypothesised to have lost their lungs because individuals with reduced, or absent, lungs were less likely to float away in the swift mountain streams where they lived. The vast majority of other salamanders possess lungs, so this makes the lungless salamanders an unusual and fascinating group of animals.

They are thought to have diverged from all other amphibian species 145 million years ago at the boundary between the Jurassic and Cretaceous periods. They are as different from all other amphibian lineages as wombats are from whales, evolving at a time when dinosaurs were still dominant. Overall, plethodontids are the most evolutionary advanced salamanders, so it may at first appear odd that they should have lost lungs, which are one of the most basic features of all vertebrates living on land. Lacking lungs and being dependent upon their skin for respiration places a size restriction on these salamanders because large animals have a relatively small surface area of skin compared to their body’s volume, and have greater difficulty in supplying their body tissues with oxygen compared to smaller animals (which have a large surface area to volume ratio). The long, slender form of the lungless salamanders maximises the surface area available for gas exchange, and some species grow to lengths of over 300 mm.

Plethodontid salamanders occupy a great diversity of habitats, ranging from strictly aquatic to strictly terrestrial, exploring niches as diverse as caves, trees, mountain streams, and they are also found burrowing through the earth. Dependence on their skin for breathing places limitations upon where and how lungless salamanders can live. Their skin must be kept moist at all times in order for oxygen to be taken up by the blood in capillaries beneath the skin. This means plethodontids are either confined to humid areas, or must find damp hiding places and only emerge in wet weather, typically at night. The life of a lungless salamander in less humid areas, like Europe and temperate North America, therefore comprises brief periods of activity interspersed with inactive phases that are often very long. They are able to survive the periods of inactivity because they have a very low metabolic rate and low energy requirements. Able to store much of what they eat as fat, they do no need to feed very often.

A further adaptation, present among many species of the lungless salamander subfamilies named “Plethodontinae” (from East and West North America) and “Bolitoglossinae” (from tropical Central and South America), is “direct development”. This is a method of amphibian development where the larval stage (e.g. the tadpole stage in a frog’s life history) has been eliminated. Early development takes place in eggs, which may be laid in moist places away from water, and the young hatch out as miniature adults. The well known amphibian metamorphosis, most commonly appreciated in the transition from tadpole to adult frog, does not occur outside of the egg. This mean that certain lungless salamanders in these two subfamilies may live away from water bodies, allowing them to expand their ranges to new areas.

The history and characteristics of the lungless salamanders go some way to explaining their range. They are mostly found in the New World, where they are widely distributed in eastern and western North America, as well as Central and South America. However, continental drift over millions of years has also brought them to the Old World, where they are found in parts Europe (e.g. Sardinia) and Korea. The existence of the Korean crevice salamander was unknown until 2005, when its discovery was a shock to science, indicating a long history of lungless salamanders in Asia. This is the only known species is Asia, suggesting that the rate of species generation in this part of the world is very low, especially compared the the huge radiation of lungless salamander species in the New World.

There is only one known species in the genus Parvimolge (commonly known as the “Mexican dwarf salamanders”), which represents one of twelve genera present within a lungless salamander subfamily called the “Bolitoglossinae”, including all the plethodontids from Central and South America. The Mexican dwarf salamanders are present in the same clade (or sub-section of the evolutionary tree of life) as another top 100 EDGE amphibian genera, Pseudoeurycea (the “false brook salamanders”). The Mexican dwarf salamanders are thought to have diverged from all other related groups before the false brook salamanders, which means their evolution as a group predates their close relative’s divergence time in Late Eocene period, at least 34 million years ago. This is around the same time that humans and moneys shared a common ancestor, so Townsend’s dwarf salamander started to evolve independently during, or slightly before, this period.
Description
Townsend's dwarf salamander, like all lungless salamanders in the Bolitoglossinae subfamily, possesses a slender body, long tail and prominent eyes. A distinctive feature of the plethodontid family is a narrow groove (the nasolabial groove) running from each nostril to the upper lip: its function is to carry waterborne odours from the ground into the nasal cavity. Another curious trait of the lungless salamanders are mental (from the Latin “mentum”, meaning chin) glands. These are modified mucus glands and release pheromones, which are chemicals produced by an animal to influence the behaviour of other members if its species, often with regard to breeding receptivity. During amplexus (the mating embrace), the male clasps the female (with both his arms and legs) and rubs pheromones across the female’s snout. Mental glands are sometimes visible in males as raised bumps below their lower lip.

Lungless salamanders are very small to medium in size, usually measuring between 25 to 250 mm from the tip of the nose to the end of the tail, which salamanders retain throughout their life. They are unusual among the salamanders in that some species can detach from their tail as a predator-defence mechanism (also known as tail or caudal autotomy). It is therefore not unusual to see individuls missing part or all of their tail, which they may regererate later. Lungless salamanders may have bold patterns on their skin as adults, or they may have a colouration more similar to their environment to aid camouflage. They have well-developed “costal” grooves (successive vertical grooves in the skin along the sides of the body), generally numbering between 10-20. Their limbs are slender and often have largely or completely webbed digits. Townsend's dwarf salamander, the only species the genus Parvimolge, is externally similar to species in the genus Thorius (the “pigmy salamanders”).

Townsend's dwarf salamander is about 50 mm in total length, with the long, tapering tail accounting for nearly half of this measurement. The head is fairly narrow, with a short, rounded snout, enlarged nostrils and protruding eyes. Small, irregularly arranged glands (seen as raised bumps on the skin) may be perceived along both sides of the back. The limbs are short and diminutive, with small hands and feet that have pointed digits. The hands and feet are nearly completely webbed. This species is brown-black in color, with light brown blotches along the dorsal (or upper) surface. The ventral surface (or underside) is lighter in colour.
Ecology
This species is closely related to the false brook salamanders (genus: Pseudoeurycea), and shares certain ecological traits with these species. Townsend’s dwarf salamander is also found in Central America (Mexico) and is partially terrestrial (ground dwelling) and also arboreal (tree-dwelling), where they are often found to inhabit a group of plants in the Neotropics called the bromeliads. Bromeliads possess overlapping leaves that may trap water and organic debris, providing a habitat for numerous species of invertebrate, amphibian and other creatures. They often occur growing on trees, attaching by structural roots to branches or bark. These bromeliads are referred to as “epiphytic”, from the Greek “epi” meaning upon and “phyton” meaning plant. The larger tank-forming bromeliads contain a number of substantial pools of water (or small aquaria) between their leaves, and therefore constitute a particularly humid micro-environment within the forest for these lungless salamanders, which are known to favour moist conditions to keep their skin hydrated for better respiration.

Direct development of the young occurs within the eggs and they hatch as miniature adults. This whole process is independent of a water body since the eggs are laid in damp locations on the land, making this a truly terrestrial (or land-dwelling) species. Many lungless salamanders in the Bolitoglossinae subfamily have been observed displaying courtship rituals. The pheromone releasing mental gland on the chin of male bromeliad salamanders plays an important role in mating to influence the receptivity of females. During amplexus (the mating embrace), the male clasps the female with both his arms and legs, and rubs pheromones across the female’s snout. Female Townsend’s dwarf salamanders probably guard the eggs throughout their development in special hides until hatching occurs, as occurs in the false brook salamander group. Townsend's dwarf salamander is capable of caudal (or tail) autotomy, which is the ability to drop the end of the tail and later regrow it. This is an antipredator mechanism that allows Townsend's dwarf salamander to escape from an attack by a predator is its tail is grabbed.
Habitat
This species inhabits cloud forest and oak forest, and is found living in bromeliads. It can survive in shaded coffee plantations, providing that humidity is retained, but is not found in heavily disturbed areas.
Distribution
This species occurs on the Sierra Madre Oriental around Cuautlpan, in east-central Veracruz, Mexico at an altitude of 800-1,500 metres above sea level.
Population Estimate
Townsend's dwarf salamander was formerly a common species, but although it has declined significantly it can still be found.
Population Trend
The IUCN Red List of Threatened Species indicates that the total population size of Townsend’s dwarf salamander is in decline.
Status
Townsend's dwarf salamander is listed as Endangered in the IUCN Red List of Threatened Species because its extent of occurrence is less than 5,000 km sq., its distribution is severely fragmented, and there is continuing decline in the extent and quality of its habitat, and in the number of mature individuals, in east-central Veracruz, Mexico. Additionally, this species is listed as "Threatened" (Amenazada) by the Mexican government.
Threats
Although this species is somewhat adaptable, it does not tolerate opening up of the landscape which leads to the drying of its microhabitats. Lungless salamanders must maintain moist skin in order to respire and therefore cannot survive in dry locations. Habitat is being lost due to expanding agriculture and human settlements, as well as the extraction of wood.
Conservation Underway
This species is not known from any protected areas, and there are currently no conservation measures underway for this species. However, it is listed as "Threatened" (Amenazada) by the Mexican government.
Projects
Conservation Proposed
Further surveys are needed to establish the current population status of this species and all information collected should then form the basis of a Conservation Action Plan. Protection of the remaining habitat for Townsend’s dwarf salamander is a major priority, which may be achieved by encouraging ecologically sensitive land uses, such as shade coffee cultivation, combined with the restoration of native habitat.
Links
References
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Parra-Olea, G., Papenfuss, T.J. and Wake, D.B. 2001. New species of lungless salamanders of the genus Pseudoeurycea (Amphibia: Caudata: Plethodontidae) from Veracruz, Mexico. Scientific papers of the Natural History Museum of the University of Kansas 20: 1-9.

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