Post by another specialist on Jan 26, 2008 16:57:29 GMT
Upper Cerro Pigmy Salamander (Thorius narisovalis)
The Upper Cerro pigmy salamander is fairly large for a Mexican pigmy salamander, and yet only grows to about 65 mm in total length. It has previously been found in the Parque Nacional Benito Suarez, and it thought to have declined by 80% over the last 15 years. It is probably threatened by habitat disturbance, as a result of agricultural expansion, human settlements, and logging. However, despite some good habitat remaining, recent surveys have been unsuccessful in locating this species. It is speculated that the adverse environmental impacts of a volcanic eruption, or even virulent disease (such as chytridiomycosis), might have contributed to the recent dramatic decline.
Distribution
North-central Oaxaca, 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 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 23 known species in the genus Thorius (commonly known as the “Mexican pigmy salamanders”) which represent one of ten genera present within a lungless salamander subfamily called the “Bolitoglossinae”, including all the plethodontids from Central and South America. The Mexican pigmy salamanders include the smallest salamanders on earth – the most diminutive of which measure just 26.9 mm in total length as sexually mature adults. Thorius salamanders occur only in Mexico, where they are restricted to the states of Veracruz, Puebla, Oaxaca and Guerrero. In general, Mexican pygmy salamanders live at high elevations, ranging from about 1,500-3,000 metres above sea level or higher, but some species descend to 800 metres above sea level.
Most Mexican pigmy salamanders lack teeth and their skulls are extraordinary because of the poor state of development, the thinness of the bones, and the weak articulation of the elements. Miniaturisation has been achieved by the reduction or loss of some of the cranial elements, accompanied by a relative increase in the size of the sense organs. Another interesting feature of these salamanders 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.
The genus Thorius is thought to have originated in the Early to Mid Miocene period, between 23 and ~12 million years ago. This makes Mexican pigmy salamanders about as dissimilar to their closest relative as humans are to gibbons. Specifically, within the Thorius salamanders the Upper Cerro pigmy salamander diverged between 5-10 million years ago.
Description
The Upper Cerro pigmy 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. 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 12-15. Their limbs are slender and often have largely or completely webbed digits. Species, like the Upper Cerro pigmy salamander, in the Thorius genus (the “Mexican pigmy salamander”) are very similar in form to those in the genus Bolitoglossa (the “mushroom-tongue salamanders”), although they are generally much small, the largest representatives seldom exceeding 70 mm in total length.
The Upper Cerro pigmy salamander is a fairly small species (although one of the large members of the genus Thorius), with a total length of around 65 mm, the relatively long tail accounting for about 35 mm of this measurement. The head is the same width as the body, the snout projecting slightly beyond the mouth with a visible “nasolabial” groove. The skin on the top and sides of the head is strongly pitted, and the skin of the tail is also pitted, as well as slightly corrugated. There are 13 “costal” grooves along each side of the body, and a further 33 folds appear along the tail. This species is reddish-brown along the entire dorsal (or upper) surface. The sides of the body are blackish and the head is a darker shade than the body. The ventral surface (or underside) is grey-brown with a few cream dots.
Ecology
Most Mexican pigmy salamanders are terrestrial (or ground-dwelling), living mainly under surface cover, inside logs, or especially beneath the bark of fallen and rotting logs. In 1908, the German naturalist Hans Friedrich Gadow in his publication “Through southern Mexico, being an account of the travels of a naturalist” remarked after observing some members of this family:
“These little things showed a predilection for living in a proverbially precarious position, namely, “between the bark and the wood” of decaying pine-trees, amongst the boring-dust of beetles and maggots.”
Upper Cerro pigmy salamanders have been found under the bark on fallen trees together with another top 100 EDGE amphibian from the same locality: Smith’s false brook salamander (Pseudoeurycea smithi). When exposed by the removal of the bark concealing their hiding places, Upper Cero pigmy salamanders are very active, quickly moving away to find cover. When touched, members of this species have been observed jumping or throwing themselves from the log to the ground and hastening away to nearby hiding places under leaves and other debris. At no time has this species been found passive or coiled up. A couple of Upper Cero pigmy salamanders have also been found on the ground under logs.
It is probable that many species of high-altitude salamander seek shelters that have a higher temperature than the surrounding area. In the Upper Cerro pigmy salamander, individuals have been found to select the smallest possible crevices under the bark on logs. These small crevices have a higher internal temperature than the larger crevices or the interiors of the logs. This species does not adapt well to the significant degradation of its habitat.
Very little is known about the Upper Cerro pigmy salamander but it is presumed that direct development of the young occurs within the eggs and they hatch as miniature adults. This whole process is independent of a water body, making this a truly terrestrial (or land-dwelling) species. Some species in the Thorius genus are known to display courtship rituals. The pheromone releasing mental gland on the chin of male Mexican pigmy 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 Mexican pigmy salamanders have been found to guard the eggs throughout their development in many species, often in special hides, until hatching occurs.
Mexican pigmy salamanders may at first appear very vulnerable to predators but a number of defense mechanisms have been found among the members of this genus. These include caudal autotomy (tail detachment) and behavioural defensive methods, including immobile posture, coiling and flipping of the body, and displays where the stomach is exposed and the tail is held up or undulated.
Habitat
The Upper Cerro pigmy salamander inhabits cloud forest and mixed forests, living under bark or fallen trees, and does not seem to survive in heavily degraded habitat.
Distribution
This species is known from Cerro San Felipe and adjacent upland areas in the Sierra de Juarez, as well as in the mountains south of La Tlaxiaco, north-central Oaxaca, Mexico, at altitudes of 2,600-3,000 metres above sea level.
Population Estimate
The Upper Cerro pigmy salamander was once extremely common, but recent attempts to find the species have been unsuccessful in locating any individuals remaining in the wild.
Population Trend
The Upper Cerro pigmy salamander is thought to be in decline by the IUCN Red List of Threatened Species, and it may already be extinct because recent surveys have failed to locate any remaining populations.
Status
The Upper Cerro pigmy salamander is listed as Critically Endangered in the IUCN Red List of Threatened Species because of a drastic population decline, estimated to be more than 80% over the last three generations, inferred from the apparent disappearance of most of the population; and because its extent of occurrence is less than 100 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. The generation length is assumed to be five years. In addition, this species is protected by Mexican Law under the "Special Protection" (Pr) category.
Threats
This species is probably being negatively impacted by habitat disturbance, as a result of agricultural expansion, human settlements, and logging, all of which are taking place extensively within its range. However, these threats do not explain the level of decline that has been observed, since the habitat is still in quite good condition in some places. It has been speculated that the adverse environmental impacts of a volcanic eruption, or even virulent disease (such as chytridiomycosis, although this normally impacts species that are associated with water), might be the cause of the recent dramatic decline.
Conservation Underway
This species occurs in Parque Nacional Benito Suarez, and is protected by Mexican Law under the category "Special Protection" (Pr).
Projects
Systematics of neotropical salamanders—Thorius, Pseudoeurycea, Chiropterotriton and Bolitoglossa:
Conservation Proposed
There is still an urgent need to conserve the cloud forest remnants that still remain in the Sierra de Juarez that provide important habitat for the Upper Cerro pigmy salamander. Research is also needed to establish the reasons for this species’ population crash, including disease screening and a thorough examination of the factors that are thought to threaten the Upper Cerro pigmy salamander. Additional surveys are also required to determine exactly where (if at all) populations survive in the wild. All of the resultant information should be used to create a Conservation Action Plan as a vital first step in galvanising efforts to preserve this species should it still survive in the wild.
If the species is found to survive in the wild, it is essential that its habitat is protected to prevent further population extinctions. In addition to conserving any remaining 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 in the specie’s range or in a foreign country that has the facilities to support a captive breeding programme for that species. Since the Upper Cerro pigmy salamander is currently categorised as Critically Endangered, the possibility of a captive breeding programme for this species should be investigated if future surveys discover any remaining populations.
Associated EDGE Community members
Prof James Hanken
James is an expert in evolutionary morphology, developmental biology, and systematics.
Links
AmphibiaWeb
Global Amphibian Assessment
Tree of Life Web Project
References
AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: amphibiaweb. Accessed: 08 December 2006.
Chippindale, P. T., Bonett, R.M., Baldwin, A.S. and Wiens, J.J. 2004. Phylogenetic evidence for a major reversal of life-history evolution in plethodontid salamanders. Evolution 58:2809-2822.
Duellman, W. E. and Trueb, L. 1986. Biology of Amphibians. McGraw-Hill, New York.
Dunn, E. R. 1926. The salamanders of the family Plethodontidae. Smith College, Northampton, Massachusetts, U.S.A.
Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.
Frost, D. R., Grant, T., Faivovich, J., Bain, R.H., Haas, A., Haddad, C. F. B., De Sá, R.O., Channing, A., Wilkinson, M., Donnellan, S.C., Raxworthy, C.J., Campbell, J.A., Blotto, B.L., Moler, P., Drewes, R.C., Nussbaum, R.A., Lynch, J.D., Green, D.M., and Wheeler, W.C. 2006. The Amphibian Tree of Life. Bulletin of the American Museum of Natural History 297: 1-370.
Gadow, H. 1908. Through southern Mexico, being an account of the travels of a naturalist. Witherby and Co., London.
Halliday, T. and Adler, C. (eds.). 2002. The new encyclopedia of reptiles and amphibians. Oxford University Press, Oxford.
IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. Global Amphibian Assessment. Accessed on 08 December 2006.
Larson, A. 1991. A molecular perspective on the evolutionary relationships of the salamander families. Evolutionary Biology 25:211-277.
Larson, A. and Dimmick, W.W. 1993. Phylogenetic relationships of the salamander families: A analysis of congruence among morphological and molecular characters. Herpetological Monographs 7:77-93.
Macey, J. R. 2005. Plethodontid salamander mitochondrial genomics: A parsimony evaluation of character conflict and implications for historical biogeography. Cladistics 21:194-202.
Min, M. S., Yang, S.Y., Bonett, R.M., Vieites, D. R., Brandon, R.A. and Wake, D.B. 2005. Discovery of the first Asian plethodontid salamander. Nature 435:87-90.
Mueller, R. L., Macey, J.R., Jaekel, M., Wake, D.B. and Boore, J.L. 2004. Morphological homoplasy, life history evolution, and historical biogeography of plethodontid salamanders inferred from complete mitochondrial genomes. PNAS 101:13820-13825.
Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A.
Parra Olea, G. & Wake, D. 2004. Thorius narisovalis. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. IUCN Red List of Threatened Species. Downloaded on 11 December 2006.
Parra-Olea, G., García-París, M. and Wake, D.B. 1999. Status of some populations of Mexican salamanders. Revista de Biologia Tropical 47: 217-223.
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.
Sever, D.M. (ed.). 2003. Reproductive biology and phylogeny of the Urodela. Science Publishers, Inc., New Hampshire, U.S.A.
Taylor, E. H. 1940. New Salamanders from Mexico, with a discussion of certain known forms. The University of Kansas Science Bulletin 26(12): pages 407-439 with 4 plates.
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.
www.edgeofexistence.org/amphibians/species_info.php?id=611
The Upper Cerro pigmy salamander is fairly large for a Mexican pigmy salamander, and yet only grows to about 65 mm in total length. It has previously been found in the Parque Nacional Benito Suarez, and it thought to have declined by 80% over the last 15 years. It is probably threatened by habitat disturbance, as a result of agricultural expansion, human settlements, and logging. However, despite some good habitat remaining, recent surveys have been unsuccessful in locating this species. It is speculated that the adverse environmental impacts of a volcanic eruption, or even virulent disease (such as chytridiomycosis), might have contributed to the recent dramatic decline.
Distribution
North-central Oaxaca, 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 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 23 known species in the genus Thorius (commonly known as the “Mexican pigmy salamanders”) which represent one of ten genera present within a lungless salamander subfamily called the “Bolitoglossinae”, including all the plethodontids from Central and South America. The Mexican pigmy salamanders include the smallest salamanders on earth – the most diminutive of which measure just 26.9 mm in total length as sexually mature adults. Thorius salamanders occur only in Mexico, where they are restricted to the states of Veracruz, Puebla, Oaxaca and Guerrero. In general, Mexican pygmy salamanders live at high elevations, ranging from about 1,500-3,000 metres above sea level or higher, but some species descend to 800 metres above sea level.
Most Mexican pigmy salamanders lack teeth and their skulls are extraordinary because of the poor state of development, the thinness of the bones, and the weak articulation of the elements. Miniaturisation has been achieved by the reduction or loss of some of the cranial elements, accompanied by a relative increase in the size of the sense organs. Another interesting feature of these salamanders 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.
The genus Thorius is thought to have originated in the Early to Mid Miocene period, between 23 and ~12 million years ago. This makes Mexican pigmy salamanders about as dissimilar to their closest relative as humans are to gibbons. Specifically, within the Thorius salamanders the Upper Cerro pigmy salamander diverged between 5-10 million years ago.
Description
The Upper Cerro pigmy 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. 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 12-15. Their limbs are slender and often have largely or completely webbed digits. Species, like the Upper Cerro pigmy salamander, in the Thorius genus (the “Mexican pigmy salamander”) are very similar in form to those in the genus Bolitoglossa (the “mushroom-tongue salamanders”), although they are generally much small, the largest representatives seldom exceeding 70 mm in total length.
The Upper Cerro pigmy salamander is a fairly small species (although one of the large members of the genus Thorius), with a total length of around 65 mm, the relatively long tail accounting for about 35 mm of this measurement. The head is the same width as the body, the snout projecting slightly beyond the mouth with a visible “nasolabial” groove. The skin on the top and sides of the head is strongly pitted, and the skin of the tail is also pitted, as well as slightly corrugated. There are 13 “costal” grooves along each side of the body, and a further 33 folds appear along the tail. This species is reddish-brown along the entire dorsal (or upper) surface. The sides of the body are blackish and the head is a darker shade than the body. The ventral surface (or underside) is grey-brown with a few cream dots.
Ecology
Most Mexican pigmy salamanders are terrestrial (or ground-dwelling), living mainly under surface cover, inside logs, or especially beneath the bark of fallen and rotting logs. In 1908, the German naturalist Hans Friedrich Gadow in his publication “Through southern Mexico, being an account of the travels of a naturalist” remarked after observing some members of this family:
“These little things showed a predilection for living in a proverbially precarious position, namely, “between the bark and the wood” of decaying pine-trees, amongst the boring-dust of beetles and maggots.”
Upper Cerro pigmy salamanders have been found under the bark on fallen trees together with another top 100 EDGE amphibian from the same locality: Smith’s false brook salamander (Pseudoeurycea smithi). When exposed by the removal of the bark concealing their hiding places, Upper Cero pigmy salamanders are very active, quickly moving away to find cover. When touched, members of this species have been observed jumping or throwing themselves from the log to the ground and hastening away to nearby hiding places under leaves and other debris. At no time has this species been found passive or coiled up. A couple of Upper Cero pigmy salamanders have also been found on the ground under logs.
It is probable that many species of high-altitude salamander seek shelters that have a higher temperature than the surrounding area. In the Upper Cerro pigmy salamander, individuals have been found to select the smallest possible crevices under the bark on logs. These small crevices have a higher internal temperature than the larger crevices or the interiors of the logs. This species does not adapt well to the significant degradation of its habitat.
Very little is known about the Upper Cerro pigmy salamander but it is presumed that direct development of the young occurs within the eggs and they hatch as miniature adults. This whole process is independent of a water body, making this a truly terrestrial (or land-dwelling) species. Some species in the Thorius genus are known to display courtship rituals. The pheromone releasing mental gland on the chin of male Mexican pigmy 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 Mexican pigmy salamanders have been found to guard the eggs throughout their development in many species, often in special hides, until hatching occurs.
Mexican pigmy salamanders may at first appear very vulnerable to predators but a number of defense mechanisms have been found among the members of this genus. These include caudal autotomy (tail detachment) and behavioural defensive methods, including immobile posture, coiling and flipping of the body, and displays where the stomach is exposed and the tail is held up or undulated.
Habitat
The Upper Cerro pigmy salamander inhabits cloud forest and mixed forests, living under bark or fallen trees, and does not seem to survive in heavily degraded habitat.
Distribution
This species is known from Cerro San Felipe and adjacent upland areas in the Sierra de Juarez, as well as in the mountains south of La Tlaxiaco, north-central Oaxaca, Mexico, at altitudes of 2,600-3,000 metres above sea level.
Population Estimate
The Upper Cerro pigmy salamander was once extremely common, but recent attempts to find the species have been unsuccessful in locating any individuals remaining in the wild.
Population Trend
The Upper Cerro pigmy salamander is thought to be in decline by the IUCN Red List of Threatened Species, and it may already be extinct because recent surveys have failed to locate any remaining populations.
Status
The Upper Cerro pigmy salamander is listed as Critically Endangered in the IUCN Red List of Threatened Species because of a drastic population decline, estimated to be more than 80% over the last three generations, inferred from the apparent disappearance of most of the population; and because its extent of occurrence is less than 100 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. The generation length is assumed to be five years. In addition, this species is protected by Mexican Law under the "Special Protection" (Pr) category.
Threats
This species is probably being negatively impacted by habitat disturbance, as a result of agricultural expansion, human settlements, and logging, all of which are taking place extensively within its range. However, these threats do not explain the level of decline that has been observed, since the habitat is still in quite good condition in some places. It has been speculated that the adverse environmental impacts of a volcanic eruption, or even virulent disease (such as chytridiomycosis, although this normally impacts species that are associated with water), might be the cause of the recent dramatic decline.
Conservation Underway
This species occurs in Parque Nacional Benito Suarez, and is protected by Mexican Law under the category "Special Protection" (Pr).
Projects
Systematics of neotropical salamanders—Thorius, Pseudoeurycea, Chiropterotriton and Bolitoglossa:
Conservation Proposed
There is still an urgent need to conserve the cloud forest remnants that still remain in the Sierra de Juarez that provide important habitat for the Upper Cerro pigmy salamander. Research is also needed to establish the reasons for this species’ population crash, including disease screening and a thorough examination of the factors that are thought to threaten the Upper Cerro pigmy salamander. Additional surveys are also required to determine exactly where (if at all) populations survive in the wild. All of the resultant information should be used to create a Conservation Action Plan as a vital first step in galvanising efforts to preserve this species should it still survive in the wild.
If the species is found to survive in the wild, it is essential that its habitat is protected to prevent further population extinctions. In addition to conserving any remaining 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 in the specie’s range or in a foreign country that has the facilities to support a captive breeding programme for that species. Since the Upper Cerro pigmy salamander is currently categorised as Critically Endangered, the possibility of a captive breeding programme for this species should be investigated if future surveys discover any remaining populations.
Associated EDGE Community members
Prof James Hanken
James is an expert in evolutionary morphology, developmental biology, and systematics.
Links
AmphibiaWeb
Global Amphibian Assessment
Tree of Life Web Project
References
AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: amphibiaweb. Accessed: 08 December 2006.
Chippindale, P. T., Bonett, R.M., Baldwin, A.S. and Wiens, J.J. 2004. Phylogenetic evidence for a major reversal of life-history evolution in plethodontid salamanders. Evolution 58:2809-2822.
Duellman, W. E. and Trueb, L. 1986. Biology of Amphibians. McGraw-Hill, New York.
Dunn, E. R. 1926. The salamanders of the family Plethodontidae. Smith College, Northampton, Massachusetts, U.S.A.
Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.
Frost, D. R., Grant, T., Faivovich, J., Bain, R.H., Haas, A., Haddad, C. F. B., De Sá, R.O., Channing, A., Wilkinson, M., Donnellan, S.C., Raxworthy, C.J., Campbell, J.A., Blotto, B.L., Moler, P., Drewes, R.C., Nussbaum, R.A., Lynch, J.D., Green, D.M., and Wheeler, W.C. 2006. The Amphibian Tree of Life. Bulletin of the American Museum of Natural History 297: 1-370.
Gadow, H. 1908. Through southern Mexico, being an account of the travels of a naturalist. Witherby and Co., London.
Halliday, T. and Adler, C. (eds.). 2002. The new encyclopedia of reptiles and amphibians. Oxford University Press, Oxford.
IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. Global Amphibian Assessment. Accessed on 08 December 2006.
Larson, A. 1991. A molecular perspective on the evolutionary relationships of the salamander families. Evolutionary Biology 25:211-277.
Larson, A. and Dimmick, W.W. 1993. Phylogenetic relationships of the salamander families: A analysis of congruence among morphological and molecular characters. Herpetological Monographs 7:77-93.
Macey, J. R. 2005. Plethodontid salamander mitochondrial genomics: A parsimony evaluation of character conflict and implications for historical biogeography. Cladistics 21:194-202.
Min, M. S., Yang, S.Y., Bonett, R.M., Vieites, D. R., Brandon, R.A. and Wake, D.B. 2005. Discovery of the first Asian plethodontid salamander. Nature 435:87-90.
Mueller, R. L., Macey, J.R., Jaekel, M., Wake, D.B. and Boore, J.L. 2004. Morphological homoplasy, life history evolution, and historical biogeography of plethodontid salamanders inferred from complete mitochondrial genomes. PNAS 101:13820-13825.
Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A.
Parra Olea, G. & Wake, D. 2004. Thorius narisovalis. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. IUCN Red List of Threatened Species. Downloaded on 11 December 2006.
Parra-Olea, G., García-París, M. and Wake, D.B. 1999. Status of some populations of Mexican salamanders. Revista de Biologia Tropical 47: 217-223.
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.
Sever, D.M. (ed.). 2003. Reproductive biology and phylogeny of the Urodela. Science Publishers, Inc., New Hampshire, U.S.A.
Taylor, E. H. 1940. New Salamanders from Mexico, with a discussion of certain known forms. The University of Kansas Science Bulletin 26(12): pages 407-439 with 4 plates.
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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