Proteus anguinus

Proteus anguinus, also known as olms, are native to countries along the Adriatic Sea. They can be found as far north as Slovenia and northern Italy, continuing southward through Croatia, and Bosnia and Herzegovina. It is uncertain whether the range continues south to Montenegro and Serbia. Isolated populations of Proteus anguinus have been introduced in the French Pyrenees Mountains and northeastern Italy. (Arnold and Burton, 1978; Arntzen, 2009; Bulog, 1999; Gasc, 1997; Sessions, 2010a; Sket, 2003; Steward, 1969)

Proteus anguinus is found in the subterranean, freshwater lakes and streams of limestone caves in the Dinaric Alps. The water in these caves is slightly acidic, contains high concentrations of oxygen, and ranges in temperature from 5° to 15° C. Adapted to an aphotic environment, olms usually reside deep within cave systems. They may be found in open streams near the surface during times of high rainfall and flooding. They are generally found over 300 meters below surface. (Arnold and Burton, 1978; Arntzen, 2009; Gasc, 1997; Steward, 1969)

Proteus anguinus has a slender, elongate body averaging 23 to 25 cm in length from head to tail. The torso is cylindrical and has about two-dozen costal grooves along each side. The tail is laterally compressed, with small fins running along the top and bottom. The head is elongate with a broad snout that is blunted at the end. Its eyes are very small and do not even breach the skin. The skin is usually creamy white, but may have a pinkish hue. When exposed to light, the skin turns dark violet to black. Darkening of the skin is reversed when it is returned to the darkness. On the ventral side of the body the skin is translucent and reveals the contours of internal organs. Directly behind the head on each side are three large, feathery, bright pink gills. This species exhibits little sexual dimorphism in appearance, but females are larger than males.

Juveniles may be distinguished from adults by the faint yellow or red blotches on their skin, and their better developed eyes. Black olms, a variant of this species previously known as Proteus anguinus parkelj, have permanently dark skin and a shorter head. (Arnold and Burton, 1978; Bulog, 1999; Sessions, 2010a; Steward, 1969)

Unlike those of most amphibians, olm larvae do not go through a distinct period of metamorphosis. Instead, the hatchling juveniles have developed directly into adults, retaining some of their larval characters such as gills and tail fins. Environmental temperature plays an important role in the development of eggs as well as juveniles. Within the range of 8° to 15°C, development time is relatively shorter (86 days) in warm temperatures and longer (182 days) in cold temperatures. (Arntzen, 2009; Bulog, 1999; Durand, 1981; Sessions, 2010a; Sessions, 2010b; Steward, 1969)

Proteus anguinus is an aseasonal breeder. During times of breeding, males become territorial and physically defend their territories. The qualities of an ideal territory are unknown. Once a mating territory is established by the male, he waits for females. Eventually a female will approach a male within his territory and courtship begins. It is unclear whether males and/or females release pheromones to communicate with each other. A male may potentially mate with multiple females, but a female mates with just one male.

The courtship process is distinctive. A female approaches a male, and he fans his tail towards her head. The male then touches the female's cloaca with his snout, and she reciprocates. The male walks in front of the female and deposits a spermatophore, which the female immediately picks up with her cloaca and stores in a special structure called a spermathecae. (Sessions, 2010a; Sessions, 2010b)

Proteus anguinus breeds every 12 years, on average. The female begins laying her fertilized eggs 2 to 3 days after courtship, and may continue to lay eggs for up to 25 days. Before laying her eggs, the female establishes an egg-laying territory away from the male's territory. Clutch size averages 35 eggs. Eggs incubate for two to six months, hatching into juveniles that develop directly into adults. Olms become sexually mature at 14 to 15 years old. (Bulog, 1999)

A female olm guards her eggs while they incubate (2 to 6 months). She does not provide food or protection once the eggs are hatched. Males exhibit no parental investment beyond the initial sperm. (Bulog, 1999; Sessions, 2010a)

Because olms live in such secluded environments, little is known about their lifespan or longevity in the wild. In fact, much of the information available concerning Proteus anguinus has been gathered from observing populations in captivity. The average age of an individual in captivity was 68.5 years, and the expected life expectancy is over 100 years. (Bulog, 1999)

Due to olms' secretive lifestyle, little information has been gathered in the wild regarding its general behavior. Usually a gregarious salamander occupying space under rocks or in cracks, Proteus anguinus only becomes territorial during times of breeding. Migratory behavior for this species is unknown, but it is expected to be mainly sedentary. (Bulog, 1999; Sessions, 2010a)

Because the adult Proteus anguinus occupies caves that are largely inaccessible to humans, the extent of an individual's range is not known. (Bulog, 1999)

Because it inhabits permanently dark environments, Proteus anguinus has developed non-visual sensory systems to better suit an aphotic lifestyle. Its eyes still retain some light sensitivity, but they are greatly reduced. Highly sensitive chemoreceptors allow olms to detect extremely low concentrations of organic material in the water. Olms use this ability to distinguish species of prey and their abundance. Functional ears, which may register sounds from the surrounding water as well as the ground, are complemented by olms' lateral line organ, which detects low-frequency water displacement in the nearby surrounding environment. All members of the genus Proteus contain an ampullary electroreceptor which is used to detect electric fields. The main function of their ampullary electroreceptor is not known, but it is suspected top be used for locating prey. Behavioral studies suggest that Proteus anguinus is also able to detect and orient itself to magnetic fields.

Little is known about the forms of intraspecies communication of olms. Potential mates have been observed using tactile stimulation – each mate touching its snout to the others cloaca. Before this, the male waves his tail in front of the female’s head. Because visual perception is minimal in the species, the purpose of such courtship behaviors is believed to be linked to pheromones and chemoreception. To establish and defend their territories, males are not known to use chemical clues, but rely on physical competition. The specialized sensory adaptations observed in olms have led scientists to use the species as a model for studying the effects of permanent darkness on the evolution of such traits. (Arntzen, 2009; Bulog, 1989; Bulog, 1999; Dumas, 1998; Sessions, 2010a)

Olms are insectivores, but will eat most anything that they can capture and fit into their mouths. They prey on arthropods and small invertebrates such as Oniscus asellus as well as organsims of the genera Belgrandiella and Niphargus. They also feed on a wide variety of insect larvae belonging to the orders Trichoptera, Ephemeroptera, Plecoptera, and Diptera. To locate and capture their prey, olms use a combination of chemoreceptors, electroreceptors, and mechanoreceptors. In captivity, olms have been recorded eating worms, tiny fish, and even small pieces of raw meat. (Bulog, 1999; Steward, 1969)

Proteus anguinus has no known predators.

As a predator of multiple different organisms, Proteus anguinus has a direct impact on the sizes of insect, arthropod, and other invertebrate populations within local subterranean freshwaters. (Bulog, 1999)

As a very distinguishable and unique creature, Proteus anguinus serves as a popular ecotourist attraction in the Dinaric Alps. It is a national treasure of Slovenia, and is so recognized by being pictured on one of the countries coins. Olms are sometimes collected for the pet trade, but doing so is illegal within the countries that protect the species. Proteus anguinus is also used in scientific research as a model for studying the evolution of highly specialized sensory adaptations in aphotic environments. (Bulog, 1999; Sessions, 2010a)

There are no known adverse effects of Proteus anguinus on humans.

Proteus anguinus is currently listed as Vulnerable on the IUCN Red List. The main cause for reduction in olm populations is habitat destruction. This may include water pollution and changes to the land above its underground habitat, such as economic development and tourism. There is also illegal capture of olms for the pet industry. Currently, Proteus anguinus mostly resides in national parks and land protected by the governments of Italy, Croatia, and Slovenia. Variant black olms are limited to a small area in Slovenia and are in need of protection. (Arntzen, 2009)