Olm
Olm | |
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Olms in Postojna Cave, Slovenia | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Amphibia |
Order: | Urodela |
Family: | Proteidae |
Genus: | Proteus Laurenti, 1768 |
Species: | P. anguinus
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Binomial name | |
Proteus anguinus Laurenti, 1768
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Subspecies | |
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Native range[a] |
The olm (German:
This
Etymology
The word olm is a German loanword that was incorporated into English in the late 19th century.[6] The origin of the German Olm or Grottenolm 'cave olm', is unclear.[7][8] It may be a variant of the word Molch 'salamander'.[7][9]
Common names
It is also called the "human fish" by locals because of its fleshy skin color (translated literally from Slovene: človeška ribica, Macedonian: човечка рипка, Croatian: čovječja ribica, Bosnian: čovječija ribica, Serbian: човечја рибица), as well as "cave salamander" or "white salamander".[10] In Slovenia, it is called močeril (from *močerъ 'earthworm, damp creepy-crawly'; moča 'dampness').[11][12]
Description
External appearance
The olm's body is snakelike, 20–30 cm (8–12 in) long, with some specimens reaching up to 40 centimetres (16 in), which makes them some of the largest cave-dwelling animals in the world.[13][14] The average length is between 23 and 25 cm.[15] Females grow larger than males, but otherwise the primary external difference between the sexes is in the cloaca region (shape and size) when breeding.[4] The trunk is cylindrical, uniformly thick, and segmented with regularly spaced furrows at the myomere borders. The tail is relatively short, laterally flattened, and surrounded by a thin fin. The limbs are small and thin, with a reduced number of digits compared to other amphibians: the front legs have three digits instead of the normal four, and the rear have two digits instead of five. Its body is covered by a thin layer of skin, which contains very little of the pigment riboflavin,[16] making it yellowish-white or pink in color.[5]
The white skin color of the olm retains the ability to produce
Sensory organs
Cave-dwelling animals have been prompted, among other adaptations, to develop and improve non-visual sensory systems in order to orient in and adapt to permanently dark habitats.
Photoreceptors
Although blind, the olm swims away from light.
Chemoreceptors
The olm is capable of sensing very low concentrations of organic compounds in the water. They are better at sensing both the quantity and quality of prey by smell than related amphibians.
Mechano- and electroreceptors
The sensory
A new type of
Like some other lower vertebrates, the olm has the ability to register weak electric fields.[19] Some behavioral experiments suggest that the olm may be able to use Earth's magnetic field to orient itself. In 2002, Proteus anguinus was found to align itself with natural and artificially modified magnetic fields.[32]
Ecology and life history
The olm lives in well-oxygenated underground waters with a typical, very stable temperature of 8–11 °C (46–52 °F), infrequently as warm as 14 °C (57 °F).[4] There have also been observations in northeastern Italy where they swim to the surface in springs outside the caves, even in daylight, where they occasionally feed on earthworms.[33] The black olm may occur in surface waters that are somewhat warmer.[4]
The olm swims by eel-like twisting of its body, assisted only slightly by its poorly developed legs. It is a
Olms are
Breeding and longevity
Reproduction has only been observed in captivity so far.[39][40] Sexually mature males have swollen cloacas, brighter skin color, two lines at the side of the tail, and slightly curled fins. No such changes have been observed in the females. The male can start courtship even without the presence of a female. He chases other males away from the chosen area, and may then secrete a female-attracting pheromone. When the female approaches, he starts to circle around her and fan her with his tail. Then he starts to touch the female's body with his snout, and the female touches his cloaca with her snout. At that point, he starts to move forward with a twitching motion, and the female follows. He then deposits the spermatophore, and the animals keep moving forward until the female hits it with her cloaca, after which she stops and stands still. The spermatophore sticks to her and the sperm cells swim inside her cloaca, where they attempt to fertilize her eggs. The courtship ritual can be repeated several times over a couple of hours.[39]
The female lays up to 70 eggs, each about 12 millimetres (0.5 in) in diameter, and places them between rocks, where they remain under her protection.[41] The average is 35 eggs and the adult female typically breeds every 12.5 years.[42] The tadpoles are 2 centimetres (0.8 in) long when they hatch and live on yolk stored in the cells of the digestive tract for a month.[41]
At a temperature of 10 °C (50 °F), the olm's
Development of the olm and other
Longevity is estimated at up to 58 years.[45] A study published in Biology Letters estimated that they have a maximum lifespan of over 100 years and that the lifespan of an average adult is around 68.5 years. When compared to the longevity and body mass of other amphibians, olms are outliers, living longer than would be predicted from their size.[42]
Taxonomic history
Olms from different cave systems differ substantially in body measurements, color, and some microscopic characteristics. Earlier researchers used these differences to support the division into five species, while modern herpetologists understand that external morphology is not reliable for amphibian systematics and can be extremely variable, depending on nourishment, illness, and other factors; even varying among individuals in a single population. Proteus anguinus is now considered a single species. The length of the head is the most obvious difference between the various populations – individuals from Stična, Slovenia, have shorter heads on average than those from Tržič, Slovenia, and the Istrian peninsula, for example.[46]
Black olm
The black olm (Proteus anguinus parkelj Sket & Arntzen, 1994) is the only other recognized subspecies of the olm. It is endemic to the underground waters near Črnomelj, Slovenia, an area smaller than 100 square kilometres (39 sq mi). It was first found in 1986 by members of the Slovenian Karst Research Institute, who were exploring the water from Dobličica karst spring in the White Carniola region.[47]
It has several features separating it from the
Feature | Proteus anguinus anguinus | Proteus anguinus parkelj | Notes |
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Skin | Not pigmented. | Normally pigmented, dark brown, or black in color. | The most obvious difference. |
Head shape | Long, slender. | Shorter, equally thick. Stronger jaw muscles visible as two bulbs on the top of the head. | |
Body length | Shorter, 29–32 vertebrae. | Longer, 34–35 vertebrae. | Amphibians do not have a fixed number of vertebrae. |
Appendages | Longer. | Shorter. | |
Tail | Longer in proportion to the rest of the body. | Shorter in proportion. | |
Eyes | Regressed. | Almost normally developed, although still small compared to other amphibians. Covered by a thin layer of transparent skin, no eyelids. | Regressed eye of White Proteus shows first of all immunolabelling for the red-sensitive cone opsin. The eye of Black Proteus has principal rods, red-sensitive cones and blue- or UV - sensitive cones.
|
Other senses | Specific and highly sensitive. | Some sensory organs, particularly electroreceptors, less sensitive. | Not very obvious. |
Proteus bavaricus
The debated species Proteus bavaricus is a close relative of the olm.[48] The species was described from a single bone, by George Brunner, and the holotype is housed in his private collection.[49][50] It was found in Bavaria's Devil's Cave, in the Pleistocene layer.[50] In his 1998 book, J. Alan Hollman described the species as a "problematic" taxon, saying that Brunner's drawing of the bone does not adequately show the differences between P. bavaricus and P. anguinus.[50]
Research history
The first written mention of the olm is in Johann Weikhard von Valvasor's The Glory of the Duchy of Carniola (1689) as a baby dragon. Heavy rains of Slovenia would wash the olms up from their subterranean habitat, giving rise to the folklore belief that great dragons lived beneath the Earth's crust, and the olms were the undeveloped offspring of these mythical beasts. In his book Valvasor compiled the local Slovenian folk stories and pieced together the rich mythology of the creature and documented observations of the olm as "Barely a span long, akin to a lizard, in short, a worm and vermin of which there are many hereabouts". [8][51]
The first researcher to retrieve a live olm was a physician and researcher from
In 1880 Marie von Chauvin began the first long-term study of olms in captivity. She learned that they detected prey's motion, panicked when a heavy object was dropped near their habitat, and developed color if exposed to weak light for a few hours a day, but could not cause them to change to a land-dwelling adult form, as she and others had done with axolotl.[8]
The basis of functional morphological investigations in Slovenia was set up by
The olm was used by Charles Darwin in his seminal work On the Origin of Species as an example for the reduction of structures through disuse:[57]
Far from feeling surprise that some of the cave-animals should be very anomalous...as is the case with blind Proteus with reference to the reptiles of Europe, I am only surprised that more wrecks of ancient life have not been preserved, owing to the less severe competition to which the scanty inhabitants of these dark abodes will have been exposed.
An olm (Proteus) genome project is currently underway by the University of Ljubljana and BGI. With an estimated genome size roughly 15-times the size of human genome, this will likely be the largest animal genome sequenced so far.[58]
Conservation
The olm is extremely vulnerable to changes in its environment, due to its adaptation to the specific conditions in caves. Water resources in the karst are extremely sensitive to all kinds of pollution.[59] The contamination of the karst underground waters is due to the large number of waste disposal sites leached by rainwater, as well as to the accidental overflow of various liquids. The reflection of such pollution in the karst underground waters depends on the type and quantity of pollutants, and on the rock structure through which the waters penetrate. Self-purification processes in the underground waters are not completely understood, but they are quite different from those in surface waters.[60]
Among the most serious chemical
The olm was included in annexes II and IV of the 1992 EU Habitats Directive (92/43/EEC). The list of species in annex II, combined with the habitats listed in annex I, is used by individual countries to designate protected areas known as 'Special Areas of Conservation'. These areas, combined with others created by the older Birds Directive were to form the Natura 2000 network. Annex IV additionally lists "animal and plant species of community interest in need of strict protection", although this has little legal ramifications.[62] Areas inhabited by the olm were eventually included in the Slovenian, Italian and Croatian parts of the Natura 2000 network.[63]
The olm was first protected in Slovenia in 1922 along with all cave fauna, but the protection was not effective and a substantial black market came into existence. In 1982 it was placed on a list of rare and endangered species. This list also had the effect of prohibiting trade of the species. After joining the European Union in 2004, Slovenia had to establish mechanisms for protection of the species included in the EU Habitats Directive. The olm is included in a Slovenian Red list of endangered species, thus its capturing or killing is allowed only under specific circumstances determined by the local authorities (e.g. scientific study).[64]
In Croatia, the olm is protected by the legislation designed to protect amphibians – collecting is possible only for research purposes by permission of the National Administration for Nature and Environment Protection.
In the 1980s the
Zagreb Zoo in Croatia houses the olm.[66][67][68] Historically, olms were kept in several zoos in Germany, as well as in Belgium, the Netherlands, Slovenia and the United Kingdom. At present they can only be experienced at Zagreb Zoo, Hermannshöhle in Germany and Vivarium Proteus (Proteus Vivarium) within Postojnska jama (Postojna Cave) in Slovenia.[69] There are also captive breeding programs in places like France.[70]
Cultural significance
The olm is a symbol of Slovenian natural heritage. The enthusiasm of scientists and the broader public about this inhabitant of Slovenian caves is still strong 300 years after its discovery.
The olm was also depicted on one of the Slovenian tolar coins.[72] It was also the namesake of Proteus, the oldest Slovenian popular science magazine, first published in 1933.[73]
Notes
References
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External links
- EDGE of Existence Olm information
- Flora and Fauna of Caves: Proteus anguinus
- Proteus magazine (in Slovene)
- Slovenian practice example: Human Fish (Proteus anguinus)
- The olm on ARKive – pictures, films
- The olm on the pages of the Slovenian Natural history museum (in Slovene)
- The Global Amphibian Assessment – Proteus anguinus