75.
El Empalme Worm Salamander
(Oedipina paucidentata)
CR
Overview
The El Empalme worm salamander inhabits lower montane rainforest, and possibly lives below the ground. There is no information on the current population status of this species because no individuals have been collected since 1952, and it is possible that the El Empalme worm salamander is now extinct. The major threat to this species is likely to be the loss of its habitat due to increased urbanisation, and expanding smallholder farming and cattle ranching.
Urgent Conservation Actions
Surveys to establish the current population status of this species; development of a Conservation Action Plan; protection of the remaining habitat.
Distribution
Cordillera de Talamanca, Costa Rica
Fact
The common name for species with in the genus Oedipina, the “worm salamanders” is derived from the fact that these salamanders have very long thin bodies and a fossorial (or burrowing) life style. This genus contains one of the largest species of lungless salamander: the collared worm salamander, Oedipina collaris, which can reach a maximum total length of 253 mm.
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 on 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 on 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 are 24 species in the genus Oedipina (commonly known as the “worm salamanders”), which represent one of twelve genera present within a lungless salamander subfamily called the “Bolitoglossinae”, including all the plethodontids from Central and South America. The worm salamanders are thought to have evolved in the Oligocene period, 23-34 million years ago. This means that the worm salamanders could have been present around the same time that humans shared a common ancestor with monkeys. Within the Bolitoglossinae subfamily of the plethodontids, only the worm salamanders and mushroomtongue salamanders (in the genus Bolitoglossa) have representatives in South America, the other genera being restricted to South America.

The worm salamanders are in the same clade (or sub-section of the evolutionary tree of life) as other top 100 EDGE amphibian genera, including Cryptotriton, Nototriton (the “moss salamanders”) and Dendrotriton (the bromeliad salamanders). An interesting feature of all of these related genera is that they possess male heterogamy reproduction – the presence of an X or Y-type sex chromosomes in the eggs and sperm, as is the case in humans. This is known as chromosomal sex determination, where females have two X sex chromosomes (XX) in their cells and males have one X chromosome and one “male” Y chromosomes (XY). In non-chromosomal sex determination, being male or female can occur as a result of environmental conditions, such as temperature, whereas with the X and Y-chromosome system, sex is determined from the outset.
Description
The El Empalme worm 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. Species, like the El Empalme worm salamander, in the genus Oedipina (the “tropical worm salamanders”) are especially elongated members of the lungless salamander family since they are adapted for a fossorial (or burrowing) lifestyle. The worm salamanders include some of the largest species within the lungless salamander family. Oedipina collaris can grow to lengths of up to 253 mm. Their common name is derived from the fact that they have very long and slender bodies, adapted for fossorial (or burrowing) lifestyles, either through the soil or beneath vegetation such as moss or decaying leaf litter.

The El Empalme worm salamander is a moderately sized species, with a total length of about 140 mm, about 90 mm of this measurement being accounted for by the relatively long, thick tail. This species has narrow head with a short and broadly rounded snout, small nostril openings and very small “nasolabial groove” skin protuberances on the upper lip. Nineteen to 20 “costal” groves may be observed in the skin along the sides of the body of this species. The fingers and toes are moderately thickened and the digits are partially webbed. The limbs are short and diminutive, with very small hands and feet. This species is brown-black in colour on the dorsal (or upper) surface and the ventral (or lower) surface is grey-black. The limbs are brownish. There have been little observed variation in the colouration of all the El Empalme worm salamanders collected so far – colouration is essentially identical in all individuals observed.
Ecology
The worm salamanders, being closely related to the Cryptotriton salamanders, moss salamanders and bromeliad salamanders, share certain ecological traits with these groups. They too are found in Central America and are partially terrestrial (ground dwelling) and may also be arboreal (tree-dwelling). However, worm salamanders are also found in South America and have also been found burrowing in the soil.

The El Empalme worm salamander is a little-studied species, although direct development of the young is known to occur 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. Some species in this genus may display courtship behaviour. The pheromone releasing mental gland on the chin of male worm 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.

Worm salamanders are known to display a lack of parental care, are both common traits of moss salamanders. Non-attendance of worm salamander eggs has often been observed in the field, and members of this genus that have laid eggs in laboratory conditions (e.g. Oedipina parvipes) showed no interest in them and exhibited no egg guarding behaviour. In most other lungless salamander genera the female guards the eggs until the hatch in a special hide. The lack of egg guarding in worm salamanders is mirrored by their close relatives, the moss salamanders (genus: Nototriton).

Most salamanders move rather slowly, but some a capable of rapid movement to escape predators. Worm salamanders are particularly adept at “lateral writhing”, where they move their extremely elongated bodies rather like a snake. Worm salamanders have other means of defense against predators – these include noxious skin secretions, caudal autotomy (tail detachment) and behavioural defensive methods, including immobile posture, coiling and flipping of the body, and displays where the tail is undulated.
Habitat
The El Empalme worm salamander inhabits lower montane rainforest, and possibly lives below the ground.
Distribution
This species is known only from the locality where it was originally formally discovered, near El Empalme (along the Pan-American Highway, south of Cartago) at the northern end of the Cordillera de Talamanca, Costa Rica, at an altitude of about 2,286 metres above sea level.
Population Estimate
There is no information on the current population status of this species because no individuals have been collected since 1952, and it is possible that the El Empalme worm salamander is now extinct.
Population Trend
The IUCN Red List of Threatened Species indicates that the total population size of the El Empalme worm salamander is in decline.
Status
The El Empalme worm salamander is listed as Critically Endangered in the IUCN Red List of Threatened Species because its extent of occurrence is less than 100 km sq., all individuals are in a single location, and there is continuing decline in the extent and quality of its habitat in the northern Cordillera de Talamanca, Costa Rica.
Threats
The major threat to this species is likely to be loss of habitat due to increased urbanisation, and expanding smallholder farming and cattle ranching.
Conservation Underway
The El Empalme worm salamander is not known from any protected area, and there are currently no conservation measures underway for this species.
Conservation Proposed
Urgent 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 the El Empalme worm salamander is also a major priority.

In addition to conserving wild habitat for this species, the IUCN Technical Guidelines for the Management of Ex situ Populations, part of the IUCN Red List of Threatened Species, recommend that all Critically Endangered species should have an ex situ population managed to guard against the extinction of the species. An ex situ population is ideally a breeding colony of a species maintained outside of its natural habitat, giving rise to individuals from that species that are sheltered from problems associated with their situation in the wild. This can be located within the species’ range or in a foreign country that has the facilities to support a captive breeding programme for that species. Further investigation is therefore required into the possibilities of establishing a captive breeding programme for any surviving populations of the El Empalme worm salamander. Captive animals could then be a source of new individuals to repopulate protected habitat.
Links
References
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Roelants, K., Gower, D. J., Wilkinson, M., Loader, S. P., Biju, S. D., Guillaume, K., Moiau, L. and Bossuyt, F. 2007. Global patterns of diversification in the history of modern amphibians. Proceedings of the National Academy of Sciences 104: 887-892.

Savage, J.M. 2002. The Amphibians and Reptiles of Costa Rica: A Herpetofauna between two Continents, between two Seas. University of Chicago Press, Chicago.

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Wake, D. B. 1966. Comparative osteology and evolution of the lungless salamanders, family Plethodontidae. Memoirs of the Southern California Academy of Sciences 4:1-111.

Wake, D. B. and Larson, A. 1987. Multidimensional analysis of an evolving lineage. Science 238:42-48.

Wake, D. B. and Lynch. J.F. 1976. The distribution, ecology and evolutionary history of plethodontid salamanders in tropical America. Natural History Museum of Los Angeles County Science Bulletin 25:1-65.

Wake, D.B. 1987. Adaptive radiation of salamanders in Middle American cloud forests. Ann. Missouri Bot. Gard. 74: 242-264.

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