Ming clams, glass sponges, when living things span the millennia
Step into a time machine to catch a glimpse of a prehistoric mammoth or travel back centuries to watch Leonardo da Vinci at work in his studio in Amboise... A very human fantasy, which can be fulfilled in rare circumstances by observing certain living organisms today that date back to ancient times.
Simon Galas, University of Montpellier
But first, how can we determine the age of a species suspected of extreme longevity? Some species can be aged thanks to a special structure in their bodies or a particular feature of their environment. This is the case for a shellfish, the Arctica islandica clam. We had to wait nearly 136 years before scientists were able to unlock its secret.
The Ming clam
It all began in the early 2000s with a study on past climates. The researchers' idea was to collect information on the chemical composition and temperature of ancient ocean water. But how could this be done? These paleoclimatologists used clams from the Kiel Museum that had been collected during an oceanographic expedition around Iceland in July 1868 and then stored in drawers at the Kiel Museum in Germany. One of these clams is called Arctica islandica.
In 2004, the team of researchers decided to examine these clams with the aim of learning more about past changes in our climate. Like tree rings, clams grow their shells each year, leaving a visible trace. By combining the analysis of these growth marks with measurements of the chemical composition of their shells, scientists were surprised to find that this clam was 373 years old. A clam that lived alongside several kings of France, including Charles VIII of Valois, FrancisI, Henry IV, Louis XVI, and even Napoleon III. Better still, in 2006, the discovery of another specimen estimated to be 405-410 years old off the coast of Iceland earned it the name "Ming," in reference to the dynasty of emperors who ruled China fromthe 14th tothe 17th century.
Hans Hillewaert/Wikipedia, CC BY-SA
Since this chance discovery, individuals aged nearly 500 years have been identified. One might be surprised by this extreme longevity and imagine that it would be difficult to match or even surpass... In fact, this is not the case! In 2004, the oceanographic exploration submarine Pisces V, belonging to the US agency NOAA and the Hawaii Undersea Research Laboratory, took coral samples off the coast of Hawaii at a depth of between 400 and 500 meters. Two species of coral, frequently plundered for use in jewelry, were particularly sought after: Gerardia sp. and Leiopathes sp. After analysis using a new carbon-14 dating technique, the results were in. These species of coral were 2,742 years old for Gerardia sp. and 4,265 years old for Leiopathes sp.!
These corals are a testament to the past, and their increasing fragility in the face of recent climate change makes them useful sentinels for understanding climate change and variations in sea temperatures. But do these organisms represent the upper limit of longevity that living animals can achieve? Perhaps not!
An 11,000-year-old glass sponge
Hermann Ehrlich, CC BY
In 1986, dredging in the East China Sea at a depth of 1,100 meters around Okinawa enabled an expedition of German, Swiss, and Chinese oceanographers to catch three specimens of a very unusual sponge called Monorhaphis chuni. This species, also known as the "glass sponge," is the only representative of its family. It lives in the deep ocean, which, like the abyss, is characterized by a total absence of light, extreme cold, and high pressure. As it grows, the glass sponge generates a kind of stem, a spiculum, composed of calcium and magnesium, which can reach a length of almost 3 meters. It is a kind of long, thin, flexible thread resembling fiberglass, which allows the sponge to anchor itself to the seabed. Chemical analysis (4) of this flexible stem has made it possible to determine the age of this sponge, which is estimated to be... 11,000 years old! In a more recent study, samples of this species of sponge, caught in the eastern and southern China Sea at depths of between 1,110 and 2,100 meters, revealed, after chemical analysis of the silica and germarium contained in the several-meter-long spicules, an estimated age of 17,000 years...
It has been suggested that the information contained in this flexible stem, which grows each year, could serve as a paleo-environmental archive for the entire Holocene geological period (a period that began 10,000 years ago and continues today). By analyzing these spicules, it is possible to determine the conditions prevailing in the ocean over the past 11,000 years and to date any changes in water temperature and composition that may have occurred. This type of living organism is obviously a godsend for those trying to find traces of the climate and its biogeochemical changes in the past. They are literally a tremendous opportunity to go back in time.
What is the secret behind these organisms? Few studies are available. However, in the case of the centuries-old clam, its great age could be linked to its ability to protect itself and eliminate damage caused by oxidation. Defenses may delay damage to their DNA or proteins caused by free radicals. However, it is possible that these organisms use other mechanisms to support their longevity.
Awaken life from the depths of time
Another characteristic of longevity is related to the ability to "fall asleep." There are a few rare organisms capable of remaining in a state of slowed or suspended life, only to wake up when conditions allow. And to study them and determine their age, we must look at their environment.
A team of Russian scientists conducted surveys between 2002 and 2015 in the permafrost of two regions of Siberia. The scientists carried out carbon dating of the layers in which they were conducting their explorations. They were thus able to discover frozen worms 3.5 meters deep in the frozen ground. After adapting their culture, they succeeded in reviving two species of worms that produced offspring. These two species (Panagrolaimus and Plectus) of frozen worms were 32,000 and 42,000 years old, respectively!
Another "awakening": in Death Valley, on the border between Nevada and California, geologists conducted surveys of soil layers corresponding to ancient salt lakes dating from 9,000 to 3,000 years ago. In salt crystals, they noticed inclusions that revealed, under a microscope, very small sticks 0.005 millimeters long.
Provided by the author, CC BY
After dissolving the salt crystals in appropriate culture media and waiting a few months, they were surprised to see the cultures become cloudy, indicating the presence of organisms. These were actually Archaea that had just awakened after more than 42,000 years of sleep in salt crystals. Although they look similar, Archaea are very different from bacteria.
Would you dare to taste a century-old wine?
Dating living organisms also means knowing what's on our plates. Foodies, did you know that determining the age of a lobster is difficult, as the technique for doing so has only been around for a very short time? Researchers have discovered that teeth located in its stomach can attest to the crustacean's age. And estimates indicate that the American species American lobster can live for over a hundred years. Two anecdotes tell of a 132-year-old lobster that was released after spending nearly 20 years in the aquarium of a restaurant on Long Island near New York, and another, around 100 years old, that was saved from the cooking pot of a Canadian restaurant by a generous donor. So, curb your appetite!
Simon Galas, Professor of Genetics and Molecular Biology of Aging, CNRS – Faculty of Pharmacy, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.