The olm: the blind cave salamander that lives to 100

By Ed Yong | July 20, 2010 7:00 pm

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

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CATEGORIZED UNDER: Ageing, Amphibians, Animals

Comments (15)

  1. zackoz

    I didn’t see the graph “below” on my screen, but after mucking around a bit, I realised it was among the small images above the post.

    Fascinating stuff – we may learn the secret of longevity from the olm, but if the price is ending up looking like it, then the price is too high.

  2. I might go to Slovenia just to have the Proteus coin

  3. dosed

    There is no mystery why the olm has such longer lifespan. It is totally expected that such an “isolated” organism free from predation and many of the dangers associated with “open” habitats, to evolve towards a longer lifespan.
    There is no advantage in having genes for living much beyond the probability of accidental death, is it?
    So, when the environment permits it, selection will favor organisms living for longer(having more offspring). There is no surprise, or mystery in seeing the olm living as long as a human being, or an elephant…
    I fail to see, from your article, why the olm “will open some promising doors into the biology of aging for years to come”.

    If you replaced the mass axis with one that accounts for predation and accidental death, that black dot would fit right in with the rest. It’s just wrong to read something from the graph, with only mass as a criteria.

  4. You’re confusing ultimate and proximate explanations.

    For general readers, ultimate explanations look at the evolutionary factors behind a trait or behaviour. Essentially, why does an animal have a trait or behaviour? The olm study doesn’t address this question, which is ably covered by dosed’s analysis.

    Proximate explanations look at the ‘how’ behind a trait or behaviour. So the olm has evolved a long lifespan – fine, but how has it achieved this? We don’t know.

  5. dosed

    No, that’s why i added the last paragraph.
    You support the assumption the authors are making. Just because the organism has a small mass, doesnt mean it should have a smaller lifespan. It is a faulty connection.

    In light of its habitat, it is to be expected to have a longer lifespan. No mystery.

    So, the olm “will open [as much] promising doors into the biology of aging for years to come” as elephants do, or human beings.

  6. Chris M.

    @dosed, the comparison is likely to be based partly on the lifespan of captive animals, which tend to avoid predation and (to a degree) accidental death. “Maximum” lifespan does attempt to take these factors into account.

    What’s interesting is that it doesn’t use the known mechanisms of avoiding aging. Clearly, we have an example of something that has improved its longevity relative to its peers, but not done so with any genetic mechanisms that we understand. It really isn’t a big surprise that it has evolved toward a longer lifespan, but to have done so very successfully without using mechanisms that we know of? Clearly it’s done something different; it seems odd to dismiss that, simply because a longer lifespan is expected for its evolutionary history.

    Anyway! Really great animals, and what may turn out to be interesting is comparing the typical olms with the black olm subspecies, which appears to be significantly less specialized for underground living, or with the other Proteidae. Since the mudpuppies are so common in the United States, it’s likely that they make up at least one of the samples in the graph, and may provide a good genetic comparison.

  7. jdmimic

    Great article, thanks for posting about it. It is interesting on multiple interrelated levels.

    Oh, and I am glad to see someone who not only knows the difference between proximal and ultimate causes, but actually makes a distinction between them.

  8. dosed

    Sorry guys but this really isn’t about proximal and ultimate explanations, which are really basic concepts and there is no special merit in making the distinction.

    From knowing the olm’s environment, we should expect it to have a longer lifespan.
    I’ll try to express my “ojection” from a different angle:
    Ed Young: “…the olm’s metabolic rate isn’t any lower than that of its much shorter-lived cousins…………the olm’s antioxidant abilities aren’t anything to shout about.”

    Here you express this observations relative to the olm’s cousins.
    Why should we expect to see a difference?
    Oxidative stress is counteracted by the cell. But there is evidence of a direct correlation (unlike the correlation between mass and lifespan) between antioxidant capabilities and lifespan? Or is it more specific to different groups?
    Can you see the difference between antioxidant capabilities of a turtle with a long lifespan and another one with a shorter lifespan? Or are they more or less the same in this respect? Same question about organisms with higher metabolic rates.
    If I am wrong I’m sure u can easily correct me.

  9. I’d venture that we don’t know enough about other salamander species to make a fair comparison with the olm. Whenever I’ve looked up longevity information about newt or salamander species, the reports are spotty – “maybe 20 or 30 years, but so-and-so zoo had one that lived to 50” kind of stuff. Very few data points.

    I suspect that many amphibian species live a lot longer than we give them credit for. This study of the olms is impressively long-ranging and detailed. Are there comparable studies of related amphibian populations?

    Also, even though some animals live longer in captivity, many are hard to keep alive because we just don’t know a whole lot about them. While I’m speculating, I’m going to say that most of our amphibian lifespan data falls into this category – so a salamander can live 50 years in a zoo cage eating crickets. Does that really tell us the maximum lifespan of its species?

  10. Emp

    Dosed, I think the point is that while we know longer lifespans can result from relatively hazard- and predator-free environments, we don’t know the exact biochemical mechanism that causes the increase in lifespan. Ultimately, knowing that mechanism may prove useful in the study of human aging as well. Just because we know something (long lifespan) is selected for does not mean we know the exact gene(s) that generate the trait, or the exact processes that have an impact on the trait in the organism in question. Thus, Ed’s mention of the normal metabolic rate and antioxidant capabilities of the olm is relevant, because it demonstrates that the mechanisms for delayed aging that many might suggest (and indeed, that many people are researching in other organisms) do not seem to apply to the olm.

  11. dosed

    @Emp, So, we agree there is no mystery(it is expected to)/(mass isn’t the valid criteria but habitat and lifestyle) in finding that a small organism like the Olm has a longer lifespan. But how he achieves it is, a mystery. But aging is just as mysterious for all organisms.

    “we don’t know the exact biochemical mechanism that causes the increase in lifespan. Ultimately, knowing that mechanism may prove useful in the study of human aging as well.”

    I would say we don’t even know the general mechanism that causes an increase in lifespan but only have some clues.
    I was asking if we should really expect to see a clear difference in antioxidant capabilities of two related species, with different lifespans…I don’t know the answer.

    The “only two” known ways of increasing lifespan, that Ed Young has covered above, are missing the most facile and obvious way: selection on fitness for longer time, which is not reflected in antioxidant capabilities. All the systemic diseases and not only, that creep in after an organism passed the “optimal age”(for his lifestyle and habitat) are not enough to explain his increase of lifespan?
    Sure, if the olm lived for a couple of hundred years we would be entitled to expect some sort of novel mechanism that increases lifespan. But the olm fits right in with most other species living in hazard- and predator-free environments.

    Sorry to bore you so much with my doubts but, when we see two men, one having a lifespan of 93 and the other of 71. Do we expect to see relevant differences in antioxidant capabilities? Or the genetic makeup for increased fitness is enough to explained it?
    My example is not so misplaced. The olm faced selection in a hazard- and predator-free environment for 20 my.

  12. Aurora

    I made sure my Inter-rail trip included Slovenia to go see the olms, and this just makes them even more fascinating! Had been mildly disappointed by coverage elsewhere, but you actually explained what Voituron & colleagues did and the significance of the whole issue – thanks, Ed!

  13. Emp

    Dosed, it’s true that there is typically little selective pressure to weed out diseases past the age of breeding (or child-rearing, if applicable) in most animals. Some of those late-onset diseases, such as most types of cancer, are common killers of animals that often manage to survive beyond their breeding years, humans being a good example. But what diseases plague other salamanders that mange to avoid predation, and do they really affect the olm at a different rate? I don’t know the answer to that, and I don’t know if scientists studying the olm do, either. The olm happens to be an interesting case because it actually lives much longer than its kin (and humans!) on average, and yet we know little about how it actually achieves this. Of course, there are likely other creatures with similarly unexplained long lifespans; maybe they’ll be the topic of a future blog post. 😛

  14. GuitarFish2760

    Do you think perhaps the reason for the Olm having such a long lifespan is because it is a cave-dweller and therefore lives in complete darkness, so isn’t exposed to sunlight? The UV element of the suns’ rays are well known for generating free radicals.
    More free radicals= more damage= a shorter lifespan.

    Has this justification been explored?

    Brilliantly- written article by the way, it was a pleasure to read :-)

  15. Chris

    “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” – Actually the olm can live for several YEARS without food which would indicate it has a very low metabolism.


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