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The olm () or proteus ( Proteus anguinus) is an aquatic salamander which is the only species in the genus Proteus of the family Proteidae and the only Troglobite chordate species found in Europe; the family's other extant genus is Necturus. In contrast to most , it is entirely aquatic animal; eating, sleeping, and breeding underwater. Living in caves found in the Dinaric Alps, it is endemic to the waters that flow underground through the extensive limestone bedrock of the karst of Central Europe and Southeastern Europe in the basin of the Soča River () near Trieste, Italy, southern Slovenia, southwestern Croatia, and Bosnia and Herzegovina. Introduced populations are found near Vicenza, Italy, and Kranj, Slovenia. It was first mentioned in 1689 by the local naturalist Valvasor in his Glory of the Duchy of Carniola, who reported that, after heavy rains, the olms were washed up from the underground waters and were believed by local people to be a cave dragon's offspring.
This cave salamander is most notable for its adaptations to a life of complete darkness in its underground habitat. The olm's are Vestigiality, leaving it blind, while its other , particularly those of olfaction and hearing, are acutely developed. Most populations also lack any pigmentation in their skin. The olm has three toes on its forelimbs, but only two toes on its hind feet. It exhibits neoteny, retaining characteristics such as external into adulthood, (2026). 9780789477644, DK. ISBN 9780789477644 like some American amphibians, the axolotl and the mudpuppies ( Necturus).
The white skin color of the olm retains the ability to produce melanin, and will gradually turn dark when exposed to light; in some cases the are also colored. One population, the black olm, is always pigmented and dark brownish to blackish when adult. The olm's pear-shaped head ends with a short, dorsoventrally flattened snout. The mouth opening is small, with tiny tooth forming a sieve to keep larger particles inside the mouth. The nostrils are so small as to be imperceptible, but are placed somewhat laterally near the end of the snout. The regressed are covered by a layer of skin. The olm breathes with external that form two branched tufts at the back of the head. They are red in color because the oxygen-rich blood shows through the non-pigmented skin. The olm also has rudimentary , but their role in respiration is only accessory, except during hypoxic conditions.
A new type of electroreception sensory organ has been analyzed on the head of Proteus, utilizing light and electron microscopy. These new organs have been described as .
Like some other lower , the olm has the ability to register weak . 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.Bulog B., Schlegel P. et al. (2002). Non-visual orientation and light-sensitivity in the blind cave salamander, Proteus anguinus (Amphibia, Caudata). In: Latella L., Mezzanotte E., Tarocco M. (eds.). 16th international symposium of biospeleology; 2002 Sep 8–15; Verona: Societé Internationale de Biospéologie, pp. 31–32.
The olm swims by eel-like twisting of its body, assisted only slightly by its poorly developed legs. It is a animal, feeding on small (for example, Troglocaris shrimp, Niphargus, Asellus, and Synurella amphipods, and Oniscus asellus), (for example, Belgrandiella), and occasionally and insect larvae (for example, Trichoptera, Ephemeroptera, Plecoptera, and Diptera). It does not chew its food, instead swallowing it whole. The olm is resistant to long-term starvation, an adaptation to its underground habitat. It can consume large amounts of food at once, and store nutrients as large deposits of and glycogen in the liver. When food is scarce, it reduces its activity and metabolism, and can also reabsorb its own tissues in severe cases. Controlled experiments have shown that an olm can survive up to 10 years without food.
Olms are Social animal, and usually aggregate either under stones or in fissures. Sexually active males are an exception, establishing and defending territories where they attract females. The scarcity of food makes fighting energetically costly, so encounters between males usually only involve display. This is a behavioral adaptation to life underground.
The female lays up to 70 eggs, each about in diameter, and places them between rocks, where they remain under her protection. The average is 35 eggs and the adult female typically breeds every 12.5 years. The tadpoles are long when they hatch and live on yolk stored in the cells of the digestive tract for a month.
At a temperature of , the olm's development (time in the eggs before hatching) is 140 days, but it is somewhat slower in colder water and faster in warmer, being as little as 86 days at . After hatching, it takes another 14 years to reach sexual maturity if living in water that is . The larvae gain adult appearance after nearly four months, with the duration of development strongly correlating with water temperature. Unconfirmed historical observations of viviparity exist, but it has been shown that the females possess a gland that produces the egg casing, similar to those of fish and egg-laying amphibians.Aljančič M., Bulog B. et al. (1993). Proteus – mysterious ruler of Karst darkness. Ljubljana: Vitrium d.o.o. Paul Kammerer reported that female olm gave birth to live young in water at or below and laid eggs at higher, but rigorous observations have not confirmed that. Historical reports of viviparity have long been attributed to scientific fraud, but may have alternatively resulted from the olms tendency to regurgitate food due to stress. These food items, including juvenile salamanders, may have been misinterpreted as their offspring. Regardless, the olm appears to be exclusively ovipary. (2026). 9781578082858, Science Publishers. ISBN 9781578082858
Development of the olm and other troglobite amphibians is characterized by heterochrony – the animal does not undergo metamorphosis and instead retains larval features. The form of heterochrony in the olm is neoteny – delayed somatic maturity with precocious reproductive maturity, i.e. reproductive maturity is reached while retaining the larval external morphology. In other amphibians, the metamorphosis is regulated by the hormone thyroxine, secreted by the thyroid gland. The thyroid is normally developed and functioning in the olm, so the lack of metamorphosis is due to the unresponsiveness of key tissues to thyroxine.
Longevity is estimated at up to 58 years.Noellert A., Noellert C. (1992). Die Aphibien Europas. Franckh-Kosmos Verlags GmbH & co., Stuttgart. 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 , living longer than would be predicted from their size.
It has several features separating it from the nominotypical subspecies ( Proteus a. anguinus):
The first researcher to retrieve a live olm was a physician and researcher from Idrija, Giovanni Antonio Scopoli, who sent dead specimens and drawings to colleagues and collectors. Josephus Nicolaus Laurenti, though, was the first to briefly describe the olm in 1768 and give it the scientific name Proteus anguinus. It was not until the end of the century that Carl Franz Anton Ritter von Schreibers from the Naturhistorisches Museum of Vienna started to look into this animal's anatomy. The specimens were sent to him by Sigmund Zois. Schreibers presented his findings in 1801 to The Royal Society in London, and later also in Paris. Soon, the olm started to gain wide recognition and attract significant attention, resulting in thousands of animals being sent to researchers and collectors worldwide. A Dr Edwards was quoted in a book of 1839 as believing that "...the Proteus Anguinis is the first stage of an animal prevented from growing to perfection by inhabiting the subterraneous waters of Carniola."
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.
The basis of functional morphological investigations in Slovenia was set up by in the 1980s. More than twenty years later, the Research Group for functional morphological Studies of the Vertebrates in the Department of Biology (Biotechnical Faculty, University of Ljubljana), is one of the leading groups studying the olm under the guidance of Boris Bulog.Bulog B. et al. (2003). Black Proteus: mysterious dweller of the Karst in Bela krajina. Ljubljana: TV Slovenia, Video tape. There are also several cave laboratories in Europe in which olms have been introduced and are being studied. These are Moulis, Ariège (France), Choranche Cave (France), Han-sur-Lesse (Belgium), and Aggtelek (Hungary). They were also introduced into the Hermannshöhle (Germany) and Oliero (Italy) caves, where they still live today.
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:Darwin C. (1859). On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray.
An olm (Proteus) genome project is currently underway by the University of Ljubljana and BGI Group. With an estimated genome size roughly 15-times the size of human genome, this will likely be the largest animal genome sequenced so far at nearly 50 .
Among the most serious chemical pollutants are chlorinated hydrocarbon , , polychlorinated biphenyls (PCBs), which are or were used in a variety of industrial processes and in the manufacture of many kinds of materials; and metals such as mercury, lead, cadmium, and arsenic. All of these substances persist in the environment, being slowly, if at all, degraded by natural processes. In addition, all are toxic to life if they accumulate in any appreciable quantity. The olm is nevertheless noted for its capability of surviving higher concentrations of accumulated PCBs than related aquatic organisms.
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 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. Habitats directive (1992) ec.europa.eu Areas inhabited by the olm were eventually included in the Slovenian, Italian and Croatian parts of the Natura 2000 network.
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). Slovenian official gazette (2002). no. 82, Tuesday 24 September 2002.
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. As of 2020 the Croatian population has been assessed as 'critically endangered' in Croatia.
, the environmental laws in Bosnia and Herzegovina and Montenegro had not yet been clarified for this species.
In the 1980s the IUCN claimed that some illegal collection of this species for the pet trade took place, but that the extent of this was unknown: this text has been copied into subsequent assessments, but by now the anecdotic claims are not considered to be indicative of a major threat. Since the 1980s until the most recent assessment in 2022 the organisation has rated the conservation status for the IUCN Red List as 'vulnerable', this because of its natural distribution being fragmented over a number of cave systems as opposed to being continuous, and what they consider a decline in extent and quality of its habitat, which they assume means that the population has been decreasing for the last 40 years.
Zagreb Zoo in Croatia houses the olm. 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. There are also captive breeding programs in places like France.
The olm was also depicted on one of the Slovenian tolar coins.
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 peninsula, for example.
Black olm
The black olm ( Proteus anguinus parkelj Sket & Arntzen, 1994) is the only recognized subspecies of the olm other than the nominate subspecies. It is endemism to the underground waters near Črnomelj, Slovenia, an area smaller than . 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.Sket B. et al. (ed.) (2003). Živalstvo Slovenije ( The animals of Slovenia). Ljubljana: Tehniška založba Slovenije.
Proteus bavaricus
A potential species, Proteus bavaricus, is speculated to be closely related to P. anguinus. The species was described from a single bone by George Brunner, and the holotype is housed in his private collection. It was found in Bavaria's Devil's Cave, in the Pleistocene layer. 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.
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".
(2026). 9788889100400, Nuova Dimensione Edizioni. ISBN 9788889100400 Additionally, there is evidence that a small number of olms were introduced to the United Kingdom in the 1940s, although it is highly likely that the animals perished shortly after being released.
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. 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.
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. Postojna Cave is one of the birthplaces of biospeleology due to the olm and other rare cave inhabitants, such as the blind cave beetle. The image of the olm contributes significantly to the fame of Postojna Cave, which Slovenia successfully utilizes for the promotion of ecotourism in Postojna and other parts of Slovenian karst. Tours of Postojna Cave also include a tour around the speleobiological station – the Proteus vivarium, showing different aspects of the cave environment. Destinacija Postojna . Retrieved 7 June 2007.
(2026). 9781461731757, Scarecrow Press. ISBN 9781461731757 It was also the namesake of Proteus, the oldest Slovenian popular science magazine, first published in 1933.
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