The olm (Proteus anguinus) is a blind, salamander-like creature with pale skin and protruding gills, which lives entirely underwater in the cave systems of Slovenia, Croatia, Bosnia and Herzegovina. It is Europe’s only fully subterranean vertebrate, and the world’s largest cave-dwelling animal.
Its penchant for complete darkness means that, up until now, virtually nothing has been documented about its reproductive processes, and knowledge about how to conserve the species through its development is relatively limited.
But the waters of the Pivka River that flow through the karst cave aquarium have proven a suitable nursery for an estimated 4,000 olms, and infrared technology has opened up the world of the enigmatic salamander for the first time.
On Monday (30 May) at 10.48am, four months after the aquarium’s female olms excited scientists by laying eggs in captivity, the long-awaited hatching took place, caught on infrared camera and shared with the public via a live feed. On Friday 3 June, a second baby was hatched.
Dr. Lilijana Bizjak Mali, from the Biotechnical Faculty at the University of Ljubljana, said: ‘The significance is not that it is the first time that proteus has laid eggs in captivity, but that this happened in a large exhibition aquarium in a major world-renowned tourist cave, and that it was successful.’
The rare footage shows the olm larva easily breaking free of its jelly-like capsule, before swimming energetically and settling on the aquarium floor.
Dr. Mali and Dr. Stanley K. Sessions from Hartwick College, New York, had previously never seen proteus embryos, and found crucial differences to the development of other amphibians when studying them under a microscope.
Dr. Stanley said: ‘While vulnerable to fungus, proteus embryos are quite resilient and not as sensitive to noise, light and other disturbances as previously believed. However, it is paramount that they are kept in a clean environment. One of the important developmental traits of proteus is that hind limb development is delayed in relation to the forelimb. We think this may explain the reduction in number of fingers and toes.’
Their research highlighted a unique chromosomal translocation in the proteus that explains why high numbers of them display testis-ova or hermaphroditism.
With this new data, scientists at the Postojna Cave hope to develop a breeding programme to further understand other genetic adaptations within the cave-dwelling species, such as its elongated snout and unseeing eyes.
It is hoped that the hatching will increase awareness about the environmental issues affecting wild proteus, such as pollution and habitat destruction.
Saso Weldt, a biologist at the Postojna Cave, said: ‘This is one more stone in resolving the puzzle of olm reproduction in nature. Perhaps, in the future, it will be possible to find eggs and young larvae of olms in nature. So far, nobody has ever seen proteus laying eggs or hatching larvae in nature.’