Meet 100-year old Salamander (Via HerpDigest)

Meet 100-year old Salamander
The Scientist, by Jennifer Welsh 7/21/07

A blind, cave-dwelling amphibian appears to live for more than 100 years, an inexplicable feat that may eventually (when explained) provide insights into aging in other species.

But first, scientists have to unravel the mystery of how the species -- known as "human fish" -- achieves such longevity. "We cannot, at this time, say how this animal manages to survive such a long time," said eco-physiologist Yann Voituron, from the Université Claude Bernard - Lyon, first author of the study published online today (July 21) in Biology Letters. He was able to calculate the animal's extreme longevity by studying over 50 years of birth and death records of a 400-animal captive breeding colony at the Station D'Ecologie Expérimental du CNRS in Moulis, France.

The human fish, also called an olm, is a small, pale salamander, weighing between 15 and 20 grams, that has evolved extreme longevity living blindly in the caves of Europe. It can also live for a year without eating and can survive in hypoxic conditions for years.

Voituron's calculations from the weekly records of the colony predicted the olm's maximum lifespan to be over 100 years, with an average lifespan of 68.5 years. The olm's longevity exceeds that of other amphibians of its size by several times, much the way humans live about four times longer than other animals their size.

Indeed, the runner-up for longest living amphibian, the giant Japanese salamander, weighs in around 25kg, 1000 times more massive than the olm. "It is rather strange to discover that [so small an] animal, weighing about 15-20 grams, is able to survive more than a century," said Voituron. "It's the first time we found this kind of profile for a vertebrate [other than humans]."

In one respect, the amphibian's longevity is not surprising, since it has a natural lack of predators, enabling it to evolve to favor long-term survival and less frequent reproduction.

In other respects, however, the human fish's ability to live 100 years makes no sense, biologically.

Several physiological traits are normally associated with long-lived animals: larger size, low metabolic rates, and high protection against oxidative stress. Examples include giant tortoises and elephants - animals that have large body masses and low basal metabolic rates.

The olm, however, doesn't show any of these traits. So why does it live so long?

John Speakman, an energetics researcher at The University of Aberdeen said in an email that the olm is "a fascinating animal." And in consideration of recent findings that the naked mole-rat, the longest-lived rodent at 28 years, is immune to elevated levels of oxidative stress, the olm "cast[s] further doubt on the oxidative stress theory of ageing."

The authors have suggested two possible explanations. The first is the animal's exceptional laziness -- it only eats about once a month, and doesn't have to run away from predators, because it has none in its natural environment. Because it doesn't extend much energy, its metabolic rate mostly stays at its baseline rates, while most animals' metabolisms are often running much above their basal rate. "This could be a way to avoid free radical production, and thus aging," said Voituron.

Their second theory, supported by data they've collected since publishing the paper, is that the olm's mitochondria function differently from normal mitochondria -- they are able to process more ATP with less oxygen, thereby reducing their free radical output. Voituron is currently learning more about the olm's mitochondrial functioning, and comparing it to other species.

Caleb Finch, an aging researcher at the University of Southern California, said he believes the human fish could be an example of "negligible senescence" -- extremely slow aging without an increase in disease or loss of reproduction.

"This is a new [longevity] example that is very valuable," said Finch. "It documents another group of vertebrates, with actual lifespan data, that show extremely slow aging."

Y. Voituron et al., "Extreme lifespan of the human fish (Proteus Anguinus): a challenge for ageing mechanisms," Biology Letters AOP July 20, 2010 DOI: 10.1098/rsbl.2010.0539