Olm

The olms animal or proteus (Proteus anguinus) is a cave-dwelling aquatic salamander of the Proteidae family. It is Europe's sole cave-dwelling chordate species. It is totally aquatic, unlike most amphibians, and feeds, rests, and reproduces underwater. It is endemic towards the waters which stream underground via the comprehensive limestone bedrock of the karst of Central and Southeastern Europe, particularly southern Slovenia, the Soa River basin close to Trieste, southwestern Croatia, Italy, and Bosnia and Herzegovina. It lives in caves spotted in the Dinaric Alps. Near Vicenza, Italy, and Kranj, Slovenia, there are introduced populations.

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The cave salamander olms are known for their adaptations to living in total darkness in their underground home. The olm's eyes are underdeveloped, making it blind, but its remaining senses, especially smell and hearing, are well developed. Its skin is also devoid of pigmentation. The forelimbs have three toes, but the rear feet have only two. Like the several American amphibians, such as the axolotl and mudpuppies, it displays neoteny, preserving larval traits such as external gills throughout adulthood (Necturus). The olm seems to be the sole species in the genus Proteus and the only European species in the family Proteidae, which also includes the genus Necturus, which is the only extant genus.

External Appearance

The body of the olm is snake-like, measuring 20–30 cm (8–12 in) in length, with certain specimens exceeding 40 centimetres (16 in). Females expand larger than males, although the cloaca region (form and size) is the principal outward difference between the sexes while breeding. The trunk is cylindrical, consistently thick, and segmented at the myomere borders having regularly spaced furrows. The tail is small, flattened laterally, and encircled by a slender fin. The limbs are short and thin, with fewer digits than other amphibians: the front legs possess three fingers rather than four, while the back legs feature two digits rather than five. Its body is coated via a fine layer of skin that is yellowish-white or pink in colour and carries very little of the pigment riboflavin. On the abdomen area of the body, the internal organs could be seen shining through.

The olm's white skin preserves the capability to make melanin, and when exposed to light, it will progressively darken; in certain circumstances, the larvae are also coloured. It does have a short, dorsoventrally flattened snout at the end of its pear-shaped head. The mouth entrance is small, and tiny teeth act as a sieve to keep bigger particles within. The nostrils are just so small that they are almost undetectable, yet they are positioned slightly laterally close to the end of the snout. A covering of skin conceals the regressed eyes. External gills, which create two branching tufts at the back of the head, allow the olm to breathe. Because the oxygen-rich blood shows via the non-pigmented skin, these are red. Although the olm possesses rudimentary lungs, they play only a minor role in respiration, unless in hypoxic settings.

Sensory Organs

Cave animals were encouraged to evolve and strengthen non-visual sense systems, among other adaptations, in an attempt to orient in and adjust to permanently dark surroundings. The sensory system of the olm has likewise evolved to cope with life in the subterranean aquatic environment. Because it can't utilise vision to navigate, the olm relies on other senses that are more developed than in surface-dwelling amphibians. It maintains larval characteristics such as a long, slender body and a broad, flattened head, allowing it to hold more sensory receptors.

Photoreceptors

The olm, while being blind, swims away from light. The eyes have been regressed, yet they still have sensation. They are hidden deep beneath the skin's dermis and are only visible in certain younger adults. Larvae possess normal eyes at first, but growing quickly stops and they begin to retreat, eventually atrophying after four months. Photoreceptive cells in the pineal body, albeit regressed, maintain visual pigment, just the same as photoreceptor cells within a regressed eye. Proteus' pineal gland is thought to have some control over physiological processes. Light sensitivity is also found in the skin, according to behavioural studies.

The pigment melanopsin, which is found inside specialised cells called melanophores, is responsible for the integument's photosensitivity. The photosensitive pigment is found in the animal's integument, according to preliminary immunocytochemical tests.

Chemoreceptors

The olm is able to detect extremely low levels of organic chemicals in the water. They are superior to comparable amphibians at detecting both the number and quality of prey through smell. In comparison to other frogs, the nasal epithelium on the internal layer of the nasal cavity as well as in the Jacobson's organ is thicker. The taste buds are located in the mouth's mucous epithelium, with the majority of them on the top surface of the tongue and near the gill cavity entrance. Those in the mouth cavity have been used to taste food, whereas those around the gills are most likely utilised to detect pollutants in the water.

Mechano and Electroreceptors

The inner ear's sensory epithelia are highly specialised, allowing the olm to pick up sound waves in the water and also vibrations from the ground. The animal is able to record sound sources due to the sensory cells' complicated functional-morphological orientation. Because this animal remains neotenic throughout the duration of its existence, it is only sometimes introduced to normal adult hearing in the air, which is likely also conceivable for Proteus, as it is with most salamanders.

As a result, in caverns where eyesight is unavailable, it would be advantageous to benefit from the underwater hearing by detecting certain sounds and eventually localising prey or other sound sources, i.e. acoustical orientation in general. Proteus' best hearing sensitivity, according to ethological research, is between 10 Hz and 15,000 Hz. By recording low-frequency adjacent water displacements, the lateral line augments inner ear sensitivity.

Light and electron microscopy were used to examine a novel form of electroreception sensory organ on Proteus' skull. Ampullary organs are the name given to these new organs.

The olms animal, like certain other lesser vertebrates, is capable of detecting weak electric fields. According to some behavioural trials, the olm could be able to orient itself using Earth's magnetic field. In 2002, it was discovered that Proteus anguinus can align itself with both natural and intentionally manipulated magnetic fields.

Ecology and Life History

The olm resides in well-oxygenated underground waters with a constant temperature of 8–11 °C (46–52 °F), with temperatures as high as 14 °C (57 °F) on rare occasions. The black olm may be found in slightly warmer surface waters. The olm's embryonic development (period in the eggs before hatching) takes 140 days at 10 °C (50 °F), although it takes longer in colder water and faster in warmer water, taking very little as 86 days at 15 °C (59 °F). If surviving in water that is 10 °C (50 °F), it needs another 14 years to reach sexual maturity after hatching.

After roughly four months, the larvae mature into adults, with the length of development substantially correlated with water temperature. Although there are unconfirmed historical reports of viviparity, it's been demonstrated that females have a gland that generates the egg coating, similar to that found in fish and egg-laying amphibians. Female olm gives rise to living offspring in water at or below 13 °C (55 °F) and lays eggs at extremely high temperatures, according to Paul Kammerer, although rigorous observations have not corroborated this. The olm seems to be an oviparous species.

The female produces up to 70 eggs, each measuring around 12 centimetres (0.5 inches) in diameter, and buries them between rocks, in which they remain safe. The adult female normally breeds every 12.5 years and produces 35 eggs on average. When the tadpoles hatch, they are approximately 2 centimetres (0.8 in) long and live for a month on yolk contained in the digestive tract cells. 

Heterochrony is a property of the olm's as well as other troglobite amphibians' development, in which the animal would not go through metamorphosis but rather preserves larval characteristics. Neoteny is a type of heterochrony within olm that combines delayed somatic development with early reproductive maturity, i.e. reproductive maturity is achieved whereas the larval outward morphology is preserved. The thyroid gland secretes the hormone thyroxine, which controls metamorphosis in many other amphibians. Because the thyroid is fully established and functioning in the olm, the absence of transformation is related to thyroxine resistance in critical tissues.

The olm salamander swims by curling its body like an eel, with only a little help from its underdeveloped legs. It is a predatory species that feed on small crustaceans (such as Troglocaris shrimp), snails, and insects on occasions. It swallows its meal whole rather than chewing it. Long-term hunger resistance is an adaptation to the olm's underground environment. It has the ability to ingest enormous amounts of food and simultaneously store nutrients in the liver as massive reserves of lipids and glycogen. When food is sparse, it slows its activity and metabolic rate, and in extreme instances, it could even reabsorb its very own tissues. Experiments have shown that an olm can go for up to ten years without eating.  

Olms are social creatures who congregate under stones or in crevices. Males who are sexually active create and defend regions where they can attract females. Due to a lack of food, fighting is energy-intensive, therefore male interactions are mainly just for show. This is a behaviour that has evolved in response to life underground.

So far, only captive reproduction has been observed. Swollen cloacas, brighter skin colour, two lines on the side of the tail, and slightly curved fins are all signs of sexual maturity in males. In females, no such alterations have been seen. Even if there is no female present, the male can begin wooing. He may then emit a female-attracting scent to drive other males away from the designated area. He begins to circle across the female and fan her with his tail as she approaches. Then he begins to use his snout to touch the female's body, while the female uses her snout to touch his cloaca. He begins to move forward with a twitching motion at a certain point, and the female follows. The animals continue to move forward until the female strikes the spermatophore with her cloaca, and at that point, she stops and stays stationary. The spermatophore adheres to her, and sperm cells swim into her cloaca, attempting to fertilise her eggs. Over the course of a few hours, the courtship process can be performed multiple times.

Taxonomic History

Body size, colour, and certain microscopic traits varied significantly between Olms from various cave systems. External morphology is not dependable for amphibian systematics and could be exceedingly changeable, based on nutrition, disease, and other circumstances; even altering within individuals in a single group, according to earlier researchers. Proteus anguinus has been grouped together as a single species. The much more evident difference between the various groups is head length; for example, people from Stična, Slovenia, possess shorter heads on average than people from Tržič, Slovenia, and the Istrian peninsula.

Black Olm

The only other recognised subspecies of the olm is the black olm. It is only found in the subsurface waters near Rnomelj, Slovenia, and is restricted to a narrow area of less than 100 square kilometres (39 sq mi). The water from Dobliica karst spring throughout the White Carniola region was initially discovered in 1986 by employees of the Slovenian Karst Research Institute.

Conservation

Because of its adaptation to cave conditions, the olm is particularly vulnerable to changes in its environment. The karst's water supplies are particularly vulnerable to pollution of any form. The enormous number of waste disposal sites leached by rainwater, and also the unintentional overflow of various liquids, have contaminated the karst subsurface waterways. Because of its adaptation to cave conditions, the olm is particularly vulnerable to environmental changes. The karst's water supplies are particularly vulnerable to pollution of any form. The enormous number of waste disposal sites leached by rainwater, and also the unintentional overflow of various liquids, have contaminated the karst subsurface waterways.

Chlorinated hydrocarbon pesticides, fertilisers, polychlorinated biphenyls, that are or have been used in a number of industrial processes and the creation of many different materials; and metals like mercury, cadmium, lead, and arsenic have been among the most dangerous chemical pollutants. Every one of these compounds lingers in the environment, slowly degrading if at all due to natural processes. Furthermore, if they collect in any significant number, they are all poisonous to life.

The olm animal has been included in EU Habitats Directive (92/43/EEC) annexes II and IV in 1992. Individual countries are using a list of species in annex II, together with the ecosystems indicated in annex I, to create protected areas called 'Special Areas of Conservation.' The Natura 2000 network was to be made up of such areas, as well as those created by the previous Birds Directive. Annex IV also includes a list of "community-interest animal and plant species in need of severe preservation," albeit this has had little legal significance. The olm-inhabited caves of Postojna, as well as other caves in Slovenia, were finally added to the Natura 2000 network. Only under specified situations specified by local authorities is it permissible to capture or kill olm (i.e. scientific study).

The olm, together with all cave animals, had first been safeguarded in Slovenia in 1922, however, the protection proved ineffective, and a large black market developed. It was listed as a rare and endangered species in 1982. The species' trade was likewise prohibited as a result of this list. Slovenia has to implement measures for the conservation of species specified in the EU Habitats Directive upon joining the European Union in 2004. A Slovenian Red List of Endangered Species includes the olm.

Cultural Significance

Slovenia's natural heritage is symbolised by the olm. Scientists and the general public are still enthralled by this Slovenian cave resident 300 years well after discovery. Owing to the olm and other uncommon cave residents, like the blind cave beetle, Postojna Cave has been one of the origins of biospeleology. The olm's picture adds greatly to Postojna Caves fame, which Slovenia successfully exploits to promote ecotourism in Postojna as well as other regions of Slovenian karst. A visit to the paleobiological station - the Proteus vivarium – is included in all Postojna Cave tours, and it shows different features of the cave ecology.

On one of Slovenia's tolar coins, the olm had also been represented. It was also the title of the oldest Slovenian popular scientific journal, Proteus, which was founded in 1933.