Ming Clams, Glass Sponges: When Life Spans Millennia
Step into a time machine to catch a glimpse of a prehistoric mammoth, or travel back through the centuries to watch Leonardo da Vinci at work in his studio in Amboise… A very human fantasy that can be fulfilled, under rare circumstances, by observing certain living organisms today that date back to ancient times.
Simon Galas, University of Montpellier
But first, how do we determine the age of a species suspected of having an extremely long lifespan? For some species, this can be done by examining a specific structure in their bodies or by analyzing a unique feature of their environment. This is the case with a shellfish known as 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 of past climates. The researchers’ goal was to gather information on the chemical composition and temperature of ancient ocean water. But how? 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 research team decided to examine these clams in order to learn more about past changes in our climate. Just like tree rings, clams grow their shells each year, leaving a visible mark. By combining the analysis of these growth marks with measurements of the chemical composition of their shells, the scientists were surprised to find that this clam was 373 years old. A clam that lived during the reigns of several French kings, including Charles VIII of Valois, FrancisI, Henry IV, Louis XVI, and even Napoleon III. Better yet: 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 that chance discovery, specimens nearly 500 years old 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, that is not the case at all! In 2004, the Pisces V oceanographic research submersible, operated by the U.S. National Oceanic and Atmospheric Administration (NOAA) and the Hawaii Undersea Research Laboratory, collected coral samples off the coast of Hawaii at depths ranging from 400 to 500 meters. Two species of coral, frequently harvested for jewelry, were particularly sought after: Gerardia sp. and Leiopathes sp. After analysis using a new carbon-14 dating technique, the results came in. These coral species were found to be 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 vulnerability to recent climate change makes them valuable indicators for understanding shifts in climate and changes 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, a dredging expedition in the East China Sea at a depth of 1,100 meters off the coast of Okinawa enabled a team of German, Swiss, and Chinese oceanographers to collect three specimens of a very unusual sponge called Monorhaphis chuni. This species, also known as the “glass sponge,” is the sole 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 produces a sort of stalk, a spicule, composed of calcium and magnesium that can reach nearly 3 meters in length. It is a long, thin, flexible strand resembling fiberglass that allows the sponge to anchor itself to the seafloor. Chemical analysis (4) of this flexible stalk has made it possible to determine the age of this sponge, which is estimated at… 11,000 years! In a more recent study, samples of this sponge species, collected in the eastern and southern parts of the South China Sea at depths between 1,110 and 2,100 meters, revealed—following chemical analysis of the silica and germarium contained within the several-meter-long spicules—an estimated age of 17,000 years…
It has been proposed that the information contained in this flexible stem, which grows each year, could serve as a paleoenvironmental archive for the entire Holocene geological period (a period that began 10,000 years ago and continues to this day). By analyzing this spicule, it is indeed possible to determine the conditions prevailing in the ocean over the past 11,000 years, as well as 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 travel 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 may be linked to its ability to protect itself and repair damage caused by oxidation. Defenses may help delay the damage caused to their DNA or proteins by free radicals. It is, however, possible that these organisms use other mechanisms to support their longevity.
Bringing to life what has come down to us from time immemorial
Another characteristic of longevity is linked to the ability to “go into hibernation.” There are a few rare organisms capable of remaining in a state of slowed or suspended life and then waking up when conditions permit. And to study them and determine their age, we must examine their environment.
A team of Russian scientists conducted surveys between 2002 and 2015 in the permafrost of two regions in Siberia. The scientists performed carbon dating on the layers they were exploring. This allowed them to discover frozen worms 3.5 meters deep in the frozen ground. After cultivating them under appropriate conditions, 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 have drilled into soil layers corresponding to ancient salt lakes dating from 9,000 to 3,000 years ago. In salt crystals, they noticed inclusions that, under a microscope, revealed tiny rods 0.005 millimeters long.
provided by the author, CC BY
After dissolving the salt crystals in suitable 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 dormancy inside salt crystals. Although they may 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 a lobster’s age is difficult, as the technique to do so has only existed for a very short time. Researchers have discovered that teeth found in its stomach can confirm the crustacean’s age. And estimates indicate that the American species American lobster can live for over a hundred years. Two stories tell of a 132-year-old lobster that was reportedly released after spending nearly 20 years in the aquarium of a restaurant on Long Island near New York, and of another, nearly 100 years old, that was saved from the pot at a Canadian restaurant by a generous donor. So, rein in your appetite!
Simon Galas, Professor of Genetics and Molecular Biology of Aging, CNRS – School of Pharmacy, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.