Olm
| Olm | |
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| Olms in Postojnska Jama, Slovenia | |
| Scientific classification | |
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| Phylum: | |
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| Genus: | Proteus
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| Species: | P. anguinus
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| Binomial name | |
| Proteus anguinus Laurenti, 1768
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| Subspecies | |
Laurenti, 1768
Sket & Arntzen, 1994 (See text) | |
Olm or Proteus (Proteus anguinus) is an amphibian, living in subterranean waters of the Dinaric karst from the Soča river basin near Trieste in Italy, through southern Slovenia and southwestern Croatia to Herzegovina. It is the only species of the Proteus genus, the only European species of the Proteidae family, and the only European cave-dwelling chordate. The other six species of the family belong to the Necturus genus which live in the surface waters of the eastern United States. It is also called human fish (translated literally from Slovenian: Človeška ribica and Croatian: Čovječja ribica), cave salamander, or white salamander.[2] Olms are wholly aquatic, breeding and living their entire lives in water.[3]
Anatomy
External appearance
The olm's body is snakelike, 20-30 centimeters long, with some specimens reaching up to 40 centimeters[4]. The torso 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 reduced number of digits - the front legs have three digits, the rear only two. Its body is covered by a thin layer of skin, which contains very little pigment, making it yellowish-white or pink in colour.[3] The internal organs can be seen shining through. The resemblance in color to human skin is the reason why the Proteus is called "humanfish" in some languages. However, olm's skin retains the ability to produce melanin. When exposed to light, it will gradually turn dark, and in some cases the tadpoles are also colored. Its pear-shaped head ends with short, dorsoventrally flattened snout. The mouth is small, with tiny teeth forming a sieve which keep larger particles inside the mouth. Nostrils are very small and imperceptible, placed somewhat laterally near the end of the snout. The atrophied eyes are covered by a layer of skin. The olm breathes with external gills, forming two branched tufts at the back of the head.[3] They are red in color because the oxygen-rich blood shows through the skin. The olm also has rudimentary lungs, but their role in respiration is only auxilliary. Sexes are alike in outward appearence, the males differ from females only by a somewhat thicker cloaca.
Sensory organs
The olm's sensory system is adapted to life in a subterranean aquatic environment. Being unable to use sight for orientation, the olm compensates with other senses, which are better developed than in amphibians living on the surface. Some body parts retain larval proportions (long, slender body and a large, flattened head), thus being able to carry a larger number of sensory receptors.
Photoreceptors
The eyes are atrophied, but retain sensitivity to light. They lie deep in the dermis, and are visible only in some cases, especially in younger adults. Tadpoles have normal eyes, but they stop developing, start regressing under the skin, and finally atrophy after four months of development.[5] The pineal body is also atrophied, but to a lesser extent, retaining some control over the physiological processes.[6] Behavioral experiments revealed that the skin itself is also sensitive to light. This sensitivity is due to pigment melanopsin inside specialised cells, the melanophores.[7][8]
Chemoreceptors
The olm is capable of sensing very low concentrations of organic compounds in the water. They are better at sensing prey by smell than related amphibians, both its quantity and its quality.[9] The nasal epithelium is thicker than in the other amphibians[10], it lies on the inner surface of the nasal cavity and in the Jacobson's organ. The taste buds can be found in the mucous epithelium of the mouth, most of them on the upper side of the tongue and on the entrance to the gill cavities. Those in the mouth cavity are used for tasting food, where those near the gills probably serve as the sensor for the chemical composition of water.
Mechano- and electroreceptors
The sensory epithelium of the inner ear is very well developed and enables the olm to sense sound waves in the water, as well as the substrate-borne vibrations. The sensory cells inside are accurately positioned, which enables the animal to discern the direction of the sound.[11] The lateral line supplements this system in sensing low-frequency water movements.
As other lower vertebrates, the olm has the ability to sense weak electrical fields[12]. The results of some behavioral experiments also suggest the olm's ability to orientate according to Earth's magnetic field. The electrosensitive cells lie in the ampular organs on the olm's head.
Development and life
The olm's embryoic development takes 120 days, after which it takes another 14 years to reach sexual maturity. The tadpoles gain adult appearance after three months, the duration of the development being strongly correlated with the water temperature.[13] Unconfirmed historical observations of vivipary exist, but it has been shown that the females posses a gland similar to those in fish and egg-laying amphibians, which produces the egg casing.[14] It was long thought that olm females gave birth to developed young at lower temperatures and lay eggs at higher, but rigorous observations did not confirm that. Today we know that the olm is oviparous.
The female lays up to 70 eggs, each of which are 12 mm in diameter, and places them between the rocks, where they remain under her protection. The tadpoles are 2 centimeters long when they hatch and live on yolk stored in their yolk sacs for a month.[15].
Characteristic for the development of the olm and other troglobite amphibians is heterochrony - the animal does not undergo metamorphosis and instead retains larval features. The form of heterochrony in olms is neoteny - slowed somatic development with normal development of the gonads. In the rest of the amphibians, the metamorphosis is regulated by the thyroxine hormone, excreted by the thyroid gland. The thyroid itself is normally developed and functioning in the olm, so the lack of metamorphosis is due to the unresponsiveness of key tissues to thyroxine.[6]
The olm swims by snake-like twisting of its body. Poorly developed legs assist only slightly with locomotion. It is a predatory animal, feeding on small crabs, snails and occasionally insects.[3] It does not chew its food, instead swallowing it whole. One of the adaptations to the underground environment is the olm's resistance to long-term starvation. It can consume large amounts of food at once, and store nutrients as large deposits of lipids and glycogen in the liver. When the food is scarce, it reduces activity and the rate of metabolism, and can also reabsorb own tissues in severe cases. Controlled experiments have shown that it can survive up to 10 years without food.[16].
They are solitary, with individuals establishing and defending their own territories. The scarcity of food makes fights too energetically costly, though, and encounters usually involve displaying only. This can be labeled as a behavioral adaptation to the life underground.
Reproduction has only been observed in captivity so far.[14] The 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 the female. It chases other males away from the chosen area, and it is thought that he secretes 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. When that happens, he starts to move forward with a twitching motion, and the female follows. Around that time he 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 fertilize her. The courtship ritual can repeat several times in a couple of hours.[14]
Variability
The olms from different cave system differ substantially in body measurements, color and some microscopic characters. Earlier researchers used this differences to support the division into 5 different species. Today we know that amphibian external morphology is not a reliable sign for systematics and Proteus anguinus remains a single species. The body shape in amphibians is very variable, and depends also on the condition of the animal, such as nourishment, illness, etc. It varies even among the individuals in a single population. The length of the head is the most obvious difference among various populations of the olm - individuals from Stična, Slovenia have shorter head in average than those from Tržič, Slovenia and the Istria peninsula, for example.
Black proteus
The black proteus (Proteus anguinus parkelj Sket & Arntzen, 1994) is the only recognized subspecies of the olm, living in the underground waters near Črnomelj, Slovenia, an area smaller than 100 km2. That makes it a Slovenian endemic. It was first found in 1986 by the members of the Slovenian Karst research institute who were exploring the water from Dobličice karst spring in the Bela krajina region.[17]
It has several features separating it from the type subspecies:[18]
| Feature | Proteus anguinus anguinus | Proteus anguinus parkelj | Notes |
|---|---|---|---|
| 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. | |
| Body length | Shorter, 29-32 vertebrae. | Longer, 34-35 vertebrae. | Amphibians do not have a fixed number of vertebrae. |
| Appendages | Shorter. | Longer. | |
| Tail | Longer in proportion to the rest of the body. | Shorter in proportion. | |
| Eyes | Atrophied. | Normally developed, although still small compared to other amphibians. Covered by a thin layer of skin, no eyelids. | Sensitive mostly to far-red light, but also to blue and ultraviolet. |
| Other senses | Very acute. | Somewhat less developed. |
These features suggest a lesser amount of adaptation to the cave environment as compared to the type subspecies. Being discovered only recently, the black proteus' biology is largely unknown. It can be observed in certain springs drawing water from underground where it comes feeding during the night.
The history of research
The olm is supposedly first pictured as 2 pairs of snakes with wings, which could represent gills, in a relief on a Venetian stone fountain, probably originating from Karst.
The first written mention of the olm is in Janez Vajkard Valvasor's The Glory of the Duchy of Carniola (1689) as a baby dragon. This was a reference to a folk story he did not really believe in. The first researcher to get live olms was a physician and researcher from Idrija, G.A. Scopoli; he sent dead specimens and drawings to some colleagues and collectors.
Joseph Nicolai Laurenti, though, was the first to briefly describe it in 1768 and give it the scientific name Proteus anguinus. It wasn't 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 animals were sent to him by Žiga Zois. Schreibers presented his findings in 1801 to The Royal Society in London, and later also in Paris. There the olm started to gain a wide recognition and attract a significant attention, which resulted into thousands of animals being sent to researchers and collectors worldwide. The basis of functional morphology research in Slovenia was set up by Dr. Lili Istenič 25 years ago. Today, the group for functional and morphological research of the vertebrates at the Department of biology (Biotechnical faculty, University of Ljubljana) is one of the world's leading groups studying the olm. There are also several cave laboratories in Europe, where the olms were introduced and are being studied. Those are Moulis (France), Kent's Cavern (England), Han-sur-Lesse (Belgium), and Aggtelek (Hungary). They were also introduced into the Hermannshöhle (Germany) and Grote Oliero (Italy) caves, where they live today.
The olm was also used by Charles Darwin in his famous The Origin of Species as an example for the reduction of structures through disuse:[19]
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.
Vulnerability and protection
The olm is very vulnerable to changes in its environment due to high specialization to constant conditions in caves. The most threatening factor is the pollution of the surface waters with pesticides and fertilizers, which trickle through the limestone foundation into the caves. Due to its rarity the olm is also interesting for collectors, which can threaten the species by taking too many animals out of the habitat.
In the European Union legislature, the olm is included in the Appendix II and the Appendix IV of the EU Habitats Directive (92/43/EEC)[20]. The goal of the Appendix II is preservation of favourable conservation status of the animal and plant species along with their habitats by protecting the species or defining special areas of conservation, which form the Natura 2000 network. Appendix IV further defines "animal and plant species of community interest in need of strict protection". Hunting or keeping a limited number of olm individuals is therefore allowed only under strictly controlled circumstances, determined by local authorities.
The olm was first protected in Slovenia in 1922 along with all cave fauna, but the protection wasn't effective and a substantial black market came into existence. In 1982 it was placed on a list of rare and endangered species, which are strictly forbidden to trade with. By joining the EU, Slovenia had to establish mechanisms for protection of the species included in the EU Habitats Directive. It is also because of this that the olm is included in a Slovenian red list of endangered species[21]. The Postojna cave and other caves where it lives were also included in the Slovenian part of the Natura 2000 network.
In Croatia, the olm is protected under the Legislature about the protection of the amphibians[22] - collecting is possible only for the research purposes by permission of the National administration for nature and environment protection. Conservation status in Bosnia and Herzegovina and Montenegro has not yet been defined.
On the IUCN Red List, the olm is listed as vulnerable because of its fragmented and limited distribution and ever-lessening population.[23]
Cultural significance
The olm is a symbol of Slovenian natural heritage. The enthusiasm of scientists and broader public about this inhabitant of Slovenian caves is still strong 200 years after its discovery. The Postojna cave is one of the birthplaces of speleobiology due to the olm and other rare cave animals living there. The olm's image largely contributes to the fame of the Postojna cave, which Slovenia successfully utilizes for the promotion of eco-tourism in Postojna and other parts of Slovenian karst. Tours of the Postojna cave also include a tour around the speleobiological station - the Proteus vivarium, showing different aspects of the cave environment.[24]
The olm was also depicted on one of the Slovenian Tolar coins, and was the namesake of Proteus, the oldest Slovenian popular science magazine, first published in 1933.
References
- ^ Template:IUCN2006 Database entry includes a range map and justification for why this species is vulnerable
- ^ Istria on the Internet - Proteus anguinus (Olm). Retrieved on 7 June 2007.
- ^ a b c d Burnie D. & Wilson D.E. (eds.) (2001). Animal. London: DK. pp. 61, 435. ISBN 0-7894-7764-5.
{{cite book}}:|author=has generic name (help) - ^ Weber A. (2000). Fish and amphibia. In: Culver D.C. et al. (ed.): Ecosystems of the world: Subterranean Ecosystems, pp. 109-132. Amsterdam: Elsevier
- ^ Durand J.P. (1973). Développement et involution oculaire de Proteus anguinus Laurenti, Urodele cavernicole. Ann. Spéléol. 28, 193-208 Template:Fr icon
- ^ a b Langecker T.G. (2000). The effects of continuous darkness on cave ecology and caverniculous evolution. In: Culver D.C. et al. (ed.): Ecosystems of the world: Subterranean Ecosystems, pp. 135-157. Amsterdam: Elsevier Cite error: The named reference "LANG01" was defined multiple times with different content (see the help page).
- ^ Hawes R.S. (1945). On the eyes and reactions to light of Proteus anguinus. Quart. Journ. Micr. Sc. N.S. 86:1-53
- ^ Kos M. (2000). Imunocitokemijska analiza vidnih pigmentov v čutilnih celicah očesa in pinealnega organa močerila (Proteus anguinus, Amphibia, Urodela) (Immunocitochemical analysis of the visual pigments in the sensory cells of the eye and the pineal organ of the olm (Proteus anguinus, Amphibia, Urodela).) PhD thesis. Ljubljana: University of Ljubljana. Template:Sl icon
- ^ Hüpop K. (2000). How do cave animals cope with the food scarcity in caves?. In: Culver D.C. et al. (ed.): Ecosystems of the world: Subterranean Ecosystems, pp. 159-188. Amsterdam: Elsevier
- ^ Dumas P. in Chris B. (1998). The olfaction in Proteus anguinus. Behavioural Processes 43: 107-113
- ^ Bulog B. (1990). Čutilni organi oktavolateralnega sistema pri proteju Proteus anguinus (Urodela, Amphibia). I. Otični labirint (Sense organs of the octavolateral system in proteus Proteus anguinus (Urodela, Amphibia). I. Otic labyrinth). Biološki vestnik 38: 1-16 Template:Sl icon
- ^ Schegel P. & Bulog B. (1997). Population-specific behavioral electrosensitivity of the European blind cave salamander, Proteus anguinus. Journal of Physiology (Paris) 91: 75-79
- ^ Durand J.P. & Delay B. (1981). Influence of temperature on the development of Proteus anguinus (Caudata: Proteidae) and relation with its habitat in the subterranean world. Journal of Thermal Biology 6(1): 53-57
- ^ a b c Aljančič M. (ed.) (1993). Proteus - skrivnostni vladar kraške teme (Proteus - mysterious ruler of Karst darkness). Ljubljana: Vitrium d.o.o. Template:Sl icon
- ^ Aljančič G. in Aljančič M. (1998). Žival meseca oktobra: Človeška ribica (Proteus anguinus) (The animal of the month of October: Olm). Proteus 61(2): 83-87
- ^ Bulog B. (1994). Dve desetletji funkcionalno-morfoloških raziskav pri močerilu (Proteus anguinus, Amphibia, Caudata) (Two decades of functional-morphological research on the olm (Proteus anguinus, Amphibia, Caudata). Acta Carsologica XXIII/19. Template:Sl icon
- ^ Sket B. et al. (ed.) (2003). Živalstvo Slovenije (The animals of Slovenia). Ljubljana: Tehniška založba Slovenije. ISBN 86-365-0410-4 Template:Sl icon
- ^ Sket B. & Arntzen J.W. (1994). A black, non-troglomorphic amphibian from the karst of Slovenia: Proteus anguinus parkelj n. ssp (Urodela: Proteidae). Bijdragen tot de Dierkunde 64:33-53.
- ^ 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.
- ^ EU Habitats directive (1992). [1].
- ^ Slovenian official gazette (2002). no. 82, tuesday 24th september 2002. Template:Sl icon
- ^ Pravilnik o zaštiti vodozemaca (2002), Državna uprava za zaštitu prirode i okoliša [2]. Template:Hr icon
- ^ IUCN Red List of Threatened Species: Proteus anguinus. Retrieved 7 June 2007.
- ^ Destinacija Postojna. Retrieved 7 June 2007.
External links
- AmphibiaWeb page for the olm
- Flora and Fauna of Caves: Proteus anguinus
- Template:Sl icon Proteus magazine
- Slovenian practice example: Human Fish (Proteus anguinus)
- The olm on ARKive - pictures, movies
- Template:Sl icon The olm on the pages of the Slovenian Natural history museum.