In the caves of Slovenia and Croatia lives an animal that’s a cross between Peter Pan and Gollum. It’s the olm, a blind, cave-dwelling salamander, also called the proteus and the “human fish”, for its pale, pinkish skin. It has spent so long adapting to life in caves that it’s mostly blind, hunting instead with various supersenses including the ability to sense electricity. It never grows up, retaining the red, feathery gills of its larval form even when it becomes sexually mature at sweet sixteen. It stays this way for the rest of its remarkably long life, and it can live past 100.
The olm was once described as a baby dragon on account of its small, snake-like body. It’s fully aquatic, swimming with a serpentine wriggle, while foraging for insects, snails and crabs. It can’t see its prey for as it grows up, its eyes stop developing and are eventually covered by layers of skin. It’s essentially blind although its hidden eyes and even parts of its skin can still detect the presence of light. It also has an array of supersenses, including heightened smell and hearing and possibly even the ability to sense electric and magnetic fields.
The caves of Slovenia and Croatia have provided the olm with safe haven for over 20 million years, but these unchanging habitats are changing quickly. Chemical pollutants leaching into the caves and the attentions of eager black market collectors have seriously hit the olm population, and it is now vulnerable to extinction. Scientists have risen to the challenge by setting up various “cave laboratories” throughout Europe to save and study this iconic species at the same time.
One such laboratory lies in Moulis, France. In 1952, a group of scientists set up several riverbed-like basins in a local cave to mimic the olm’s natural habitat. The animals are protected and regularly fed. Sixty years on, there are more than 400 individuals in the cave, making it the only successful olm breeding programme in the world. And ever since 1958, researchers have been recording births and deaths among the olms on a weekly basis. Thanks to their painstaking census, we now have a unique glimpse into this odd creature and how it lives as long as it does.
Yann Voituron from the University of Lyon has analysed the five decades of data and found that the oldest olms are around 48-58 years old. Still, they show no sign of age-related physical decline. Based on the adults’ survival rates, Voituron calculated that the species lives to an average age of 69 years, supporting reports of captive olms living to 70.
Across different animal groups, the average lifespan can be anywhere from 10-67% of the maximum one. This means that at the very least, the oldest olms should be able to hit a respectable age of around 102 years and it may well live for even longer. Perhaps Voituron’s grandchildren will be able to check up on the same olms that he’s now studying.
Among back-boned animals, the bigger you are, the longer you live (generally speaking – there are exceptions). Whales, elephants and giant tortoises all top the longevity record books, but the humble olm can reach a century while weighing in at a puny 20 grams. The only other amphibian to even approach its lifespan is the giant salamander, which is a thousand times heavier. You can see how unusual the olm is in the graph below in the gallery above, which plots the lifespan of living amphibians against their mass. The olm is the black dot, looming over the clustered throng of white ones.
The deeper mystery here is how the olm achieves such a long life. The standard explanation says that ageing is the result of the very chemical reactions that power our lives. These reactions furnish us with energy but produce highly reactive molecules called free radicals, which damage any DNA or protein that they touch. Over the years, this constant barrage takes a toll on our bodies and ageing is the result; longer lives can therefore be achieved by stopping the onslaught of free radicals, so the story goes.
There are two main ways of doing this, but neither applies to the olm. Reducing your metabolism could do the trick. Since free radicals are the by-products of energy-producing chemical reactions, species that opt for life in the slow lane will produce less of them. As a group, salamanders are hardly go-getters, but the olm’s metabolic rate isn’t any lower than that of its much shorter-lived cousins. An alternative is to cope with the steady flow of free radicals with antioxidants that neutralise them. But again, the olm’s antioxidant abilities aren’t anything to shout about.
Something else must be happening in this bizarre creature and for now, it’s a mystery that goes unsolved. Voituron thinks that this tiny salamander will open some promising doors into the biology of ageing for years to come.
It might have something to do with the predator-free nature of the olm’s caves. Species that can escape from an early death often live longer than their peers, including birds and bats that can take to the air, and tree-dwelling mammals that can hide among the branches. Perhaps the safety of the olm’s home has allowed it to evolve an extreme lifespan without sacrificing its metabolism. Indeed, Darwin himself commented on the safety of the olm’s caves in his famous tome On the Origin of the Species:
“Far from feeling surprise that some of the cave-animals should be very anomalous…as is the case with 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 scanty inhabitants of these dark abodes will have been exposed.”
Reference: Biology Letters http://dx.doi.org/10.1098/rsbl.2010.0539
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