As William and Mary were crowned King and Queen of England, marking the end of the Glorious Revolution and economic dominance of the Dutch Republic, a much less momentous event was taking place. About six hundred miles from the Palace of Westminster, an encyclopedia was published by Johann Weikhard von Valvasor, a historian, scientist, and traveler from southeastern Europe. Spanning over three-thousand pages, the text contains the first known mention of both vampires and cave salamanders, the latter thought to be the offspring of dragons by locals. These legends arose after the pale, writhing creatures were washed out into the surface world by heavy storms; at the time, the existence of European cave fauna was largely unknown.
The species swept from its caverns was not described scientifically until eight decades later, when a specimen was brought to an Austrian naturalist who named the animal Proteus anguinus. The name refers to the shapeshifting, prophetic sea god Proteus of the Greeks and the Latin word for snake, anguis, though it is commonly referred to as an olm. Although Proteus could function quite well as either the name for an English Mastiff or the generic form of a blood-thinning medication, it is not the most descriptive name for Europe’s dragons. Indeed, the name’s shapeshifting implications would be better suited for a salamander species which does not exhibit neoteny—a state where the sexually mature form of a species retains characteristics from its juvenile stages of life.
If you think back far enough, you might recall the charts your kindergarten teacher showed you describing the stages of a frog’s life cycle, beginning with an egg which becomes a tadpole, continues to a froglet phase, and ultimately achieves the mature form of the animal. A salamander’s life cycle is similar, but instead of tadpoles and froglets there exists a larval stage, an anatomical phase along a continuum from the newly hatched salamander to the terrestrial adult without a tail fin or gills. However, given that P. anguinus spends its entire life underwater, inhibition of the final stages of transformation allows the organism to remain fully aquatic. This can also be observed in its more well-known relative, the axolotl, which spends its entire life in the waters of Lake Xochimilco in central Mexico. In fact, the cute tufts on the sides of both the olm and the axolotl are their neotenic gills, which are otherwise absorbed into the body for nutrients in species that undergo metamorphosis into standard, terrestrial salamanders. However, unlike their Mexican relatives(1), the olm’s post-larval form cannot be induced by placing it in shallow water, though the reasons for this are unknown.
Given the early discovery and peculiarity of the little dragon, it has attracted a great deal of scientific attention. In the early years of olm experimentation, a cistern at the University of Vienna was used to house a small population of the slender creatures. The man in charge of the procedures, Dr. Paul Kammerer, claimed that olms were capable of giving birth in colder waters, whereas eggs would be laid in warmer ones. These assertions were backed by reports from the 19th century, including this detailed statement from a county judge:
“On June 17, 1852 I, as well as members of my family and members of my neighbor’s families, witnessed the birth of a young olm.”
-Geck von Verch
Unfortunately, Kammerer was later accused of having forged results to support an unproven hypothesis, which shed doubt on much of his previous work. Despite some reasons to believe that Kammerer was innocent, the accusations proved too much to handle; it was not long before his body was found, gun in hand, in the Austrian mountains. Thus, considering that reports for live birth are either old, dubious, or both, it is unclear whether olms are capable of doing so.
Nevertheless, the studies performed on this organism are fascinating, and one of the most recent projects hopes to sequence the entire genome of the cave salamanders. The salamander family is renowned for its immense genomes, and the olm seems to surpass all of its genomically well-endowed cousins in the surface world. Researchers claim that the olm’s cells have about fifteen times more DNA than a human’s, resulting in the largest known genomes in the animal kingdom. To highlight just how enormous this is, consider this article, around 10,000 characters long. If you can imagine what four and a half million copies would look like, you’ll have a good idea of how much genetic information is encoded in each of this subterranean creature’s cells.
Due to the high activity of retrotransposons, salamander genomes have become far larger than those of most animals. Think of retrotransposons as a genetic copy-and-paste mechanism—assuming the copy is not inserted into a functional part of DNA, the genome may continue to expand, notwithstanding the cellular costs associated with an increase in DNA. Most organisms have introns in their DNA, or regions that do not encode for proteins. The proliferation of retrotransposons can result in huge introns, which means that cells will take longer to divide. Studies of our aforementioned Mexican friends have suggested that these large genome sizes might be what allow salamanders to regrow body parts(2), as slower cellular development results in less of a distinction between different kinds of salamander tissue. Once cells are damaged, they are able to return to an embryonic state until the lost body part is regenerated. Thus, continued studies of the olm may provide valuable insight into how genomes evolve and how humans might use regeneration to grow tissue.
The olm is even mentioned in one of the most famous (or infamous, depending on your worldview) texts in human history:
“Far from feeling any surprise that some of the cave-animals should be very anomalous, … as is the case with the blind Proteus, … I am only surprised that more wrecks of ancient life have not been preserved, owing to the less severe competition to which the inhabitants of these dark abodes will probably have been exposed.”
-Charles Darwin, On the Origin of Species, 1859
Barring Charlie’s insinuation that this adorable creature is, in truth, a wreck, it is interesting that few caves boast an abundance of organisms. You’ll hear no complaints from the olm, however. Despite its small stature, it is the apex predator of its watery underworld, which consists of a variety of locations throughout Slovenia, Croatia, and Bosnia-Herzegovina, as well as a small corner of northeastern Italy. This is a considerable range for a troglobite, or cave-dwelling organism. For comparison, consider the Alabama cave shrimp, a troglobite found only a few hours from my university. The animal’s known range was confined to a few caves in the same county until a 2019 report introduced a seventh cave in the adjacent county with a whopping six shrimp. I should also mention that the discovery of this colossal population was the result of two separate surveys a year apart, each yielding two and four organisms, respectively.
Because troglobites are highly adapted to their subterranean environments, they are unable to survive on the surface, which means that travelling to other caves is impossible unless the caves are connected underground. Thus, organisms are often confined to a single cave either until the species goes extinct or until a passage to another cave opens. Due to high adaptation to their subterranean environments, troglobites are extremely susceptible to environmental change, especially from pollutants like heavy metals or pesticides. An accident in, or poor management of, an industrial facility may release enough toxins to devastate a cave’s fauna beyond repair, and given that most troglobites inhabit narrow ranges, there are few places to turn to once a cave is contaminated. Moreover, even if a connection to another cave is present, pollutants may be able to travel throughout these systems just as well as the native troglobites. As such, many cave-dwelling organisms are at risk of extinction, including our beloved olm.
Sadly, olms are far from the only amphibians in such a predicament. The International Union for Conservation of Nature, known for its Red List of Threatened Species, lists two out of every five amphibian species at risk for extinction. Despite their potential for developing medicines, many amphibians are past the point of no return, with the only hope of surviving in the hands of the species driving their extinctions. The olm is itself listed as vulnerable, the least worrisome category for a threatened species, though its specific physiological requirements could easily knock it down to the endangered or critically endangered categories should any significant changes occur to their environment. These problems are exacerbated by the fact that female olms only produce eggs every dozen years or so, and any offspring resulting from these rare clutches must survive for fifteen years to reach sexual maturity. Fortunately, conservation efforts are underway in Slovenia(3) and a large population of olms is held in a French cave for research, thus ensuring that the species can be reintroduced to its natural habitat if necessary.
An amphibian’s lifespan typically correlates with its body mass, with heavier amphibians outliving lighter ones. Ever enigmatic, the olm defies this pattern with an average life expectancy of seven decades and an estimated maximum age of over a hundred years even though it rarely exceeds twenty grams. For comparison, the iPhone 12 weighs about 164 grams, or eight large olms. The baby dragon’s closest competitor in the Amphibian Longevity Olympics, the Japanese giant salamander, fails to surpass these ages despite often weighing as much as a thousand olms. I like to imagine that as Louis Armstrong perfected his trumpeting, fascist sentiments boiled in Europe, and F. Scott Fitzgerald penned the book that would highlight the decadence of the 1920s, a little olm patiently laid her clutch of eggs in the Stygian depths of an unmarked cave. Throughout the past century, one of her offspring feasted on shrimp, explored its domain, and had a few olms of its own; now, weary from its long life, it will soon rest, all the while oblivious to the chaos of man.
(1) Although olms have not been documented morphing into a terrestrial form, axolotls occasionally undergo this transformation. Here is an especially informative video which, other than the expected butchering of a Nahuatl word, presents an exceptionally accurate and carefully detailed overview of this process:
(2) The regeneration process is depicted in the following video, released by the Postojna Cave YouTube channel:
(3) A cave system in Slovenia where many olms live, containing a tank of specimens for public viewing:
Axolotl, photo from KinEnriquez and used under Pixabay License.
Arne Hodalič, CC BY-SA 3.0 , via Wikimedia
Joseph Nicolaus Laurenti, Public domain, via Wikimedia Commons
Niemiller ML, Inebnit T, Hinkle A, Jones BD, Jones M, Lamb J, Mann N, Miller B, Pinkley J,
Pitts S, Sapkota KN, Slay ME (2019) Discovery of a new population of the federally endangered Alabama Cave Shrimp, Palaemonias alabamae Smalley, 1961, in northern Alabama, Subterranean Biology 32: 43-59. https://doi.org/10.3897/subtbiol.32.38280,
CC0, via Wikimedia Commons
The U.S. Army, Public domain, via Wikimedia Commons
Johann Weikhard von Valvasor, Public domain, via Wikimedia Commons
Arntzen et al. 2009. Proteus anguinus. The IUCN Red List of Threatened Species.
Girijala, R. L., & Bush, R. L. 2018. Review of Socioeconomic Disparities in Lower Extremity
Amputations: A Continuing Healthcare Problem in the United States. Cureus, 10(10).
Ley, Willy. 1967. Epitaph for a lonely olm. Galaxy Science Fiction, 95-104.
Mendelson et al. 2006. Confronting Amphibian Declines and Extinctions. Science, 373(5783),
More than 37,400 species are threatened with extinction. 2021. The IUCN Red List of Threatened
Species. Retrieved from https://www.iucnredlist.org/
Niemiller et al. 2019. Discovery of a new population of the federally endangered Alabama cave
shrimp, Palaemonias alabamae Smalley, 1961, in northern Alabama. Subterranean
Biology, 32, 43-59. https://doi.org/10.3897/subtbiol.32.38280
Proteus Genome Project. 2021. Retrieved from https://www.proteusgenome.com/
Romero, Aldemaro. 2009. Cave Biology: Life in Darkness. Cambridge University Press.
Sessions, S. K., & Wade, D. B. 2020. Forever young: Linking regeneration and genome size in
salamanders. Developmental Dynamics. https://doi.org/10.1002/dvdy.279
Sket, Boris. 1997. Distribution of Proteus (Amphibia: Urodela: Proteidae) and its possible
explanation. Journal of Biogeography, 24(3), 263-280.
Swingle, W. W. 1922. Experiments on the metamorphosis of neotenous amphibians. Journal of
Experimental Zoology, 36(4), 397-421. http://doi.org/10.1002/jez.1400360402
The great feat of translation Valvasor is over. 2012. Radio-Television Slovenia. Retrieved from
Voituron et al. 2011. Extreme lifespan of the human fish (Proteus anguinus): a challenge for
ageing mechanisms. Biology Letters, 7(1), 105-107. https://doi.org/10.1098/rsbl.2010.0539