As we get older, we sometimes look back at fond memories from younger years and wish that we might be able to return to those simpler times, aging in reverse, especially when we are experiencing times of turbulence.
A recent discovery has revealed that a marine creature has taken this approach rather literally when in dire situations, regressing its physical adult body to a juvenile stage once the stress from injury or starvation has subsided; essentially aging in reverse.
The Immortal Jellyfish
Amidst the cycle of life and death, there was only one creature that we were aware of that is truly extraordinary, the turritopsis dohrnii also called the immortal jellyfish. This tiny creature has been drifting along since before the demise of the dinosaurs 66 million years ago, it is most likely smaller than the nail on your pinky finger, but it was the one and only known biologically immortal animal on Earth.
When the immortal jellyfish grows old or is damaged it evades death by reverting to a baby polyp stage by reabsorbing its tentacles and entering a resting stage as a “blob” of undifferentiated cells lying on the seafloor, essentially aging in reverse. Then the young polyp will eventually produce new adult forms. Interestingly enough, the mature buds are genetically identical to the polyp.
This hydrozoan was first described by scientists in 1883, but its eternal life cycle wasn’t known until it was accidentally discovered by experts a century later. Since then, its backward life cycle has earned it the nickname of the “Benjamin Button Jelly” in reference to F Scott Fitzgerald’s fictional character who he describes as aging in reverse (born old and dies young).
Studies have shown that colonies of immortal jellyfish kept in captivity can regress, aging in reverse, into the polyp stage and begin life anew up to 10 times in 2 years. This species may have originated in the Mediterranean but it is now in every ocean in the World. The immortal jellyfish is the only known species that can rejuvenate after sexual reproduction, making it biologically immortal.
Warty Comb Jellyfish Enters The Arena
Previously the immortal jellyfish was thought to be the only species that was capable of aging in reverse to jelly puberty, now this discovery put this Comb Jelly (Mnemiopsis leidy) which is better known as the Sea Walnut or Warty Comb Jelly in the same amazing rejuvenating category.
Comb jellyfish were already known to be special with unmatched regenerative abilities, the ability to fuse together and survive major injuries, only forming a butthole when they need it, and with disregard to biology, they can reproduce sexually in their larval stage.
Previously the comb jelly was observed to reduce its size and mass during periods of starvation to help it survive, but at the time experiments ruled out age-reversing under those conditions.
More recently, marine biologist Joan Soto-Angel, from the University of Bergen in Norway observed the plump gelatinous lobes that define adulthood in this species suddenly disappear on an adult, and in its place pulsed a larva with a more walnut shell shape than any other adult. This prompted the investigation into whether this jelly had just somehow managed to press rewind, allowing it to begin aging in reverse.
Investigating The Backward Life Cycle
65 healthy adult comb jellyfish that had completely reabsorbed their juvenile tentacles were kept isolated in tanks. They were all starved for 15 days, then fed a small amount of a lean diet once a week. As expected, the jellyfish began to shrink, and when they began to reabsorb into their diminishing bodies the feeding schedule was resumed to every second day. Additionally, 15 jellyfish had lobes surgically removed at the start of the experiment to add a further stressor not included in previous research.
Aging In Reverse
“Over several weeks, they not only reshaped their morphological features, but also had a completely different feeding behavior, typical of a cydippid larva,” said Soto-Angel. “Witnessing how they slowly transition to a typical cydippid larva, as if they were going back in time, was simply fascinating.”
These findings published in PNAS showed that these jellyfish were capable of aging in reverse to a youthful form, but only when stressed by starvation, however, this was less common in the group with surgical lobe removal. Only 7 of the 50 starved jellyfish fully reverted, while only 6 out of the 15 injured animals reverted to being the equivalent of 17 again.
“It will be interesting to reveal the molecular mechanism driving reverse development, and what happens to the animal’s nerve net during this process,” says study collaborator Pawel Burkhardt, who is leading investigations into the evolutionary origins of neurons.
“The fact that we have found a new species that uses this peculiar ‘time-travel machine’ raises fascinating questions about how spread this capacity is across the animal tree of life,” said Soto-Angel.
Comb jellyfish are among the earliest animal lineages, findings suggest that this aging in reverse development may represent an ancient feature in the animal kingdom.
“This is a very exciting time for us”, Burkhardt said. “This fascinating finding will open the door for many important discoveries. It will be interesting to reveal the molecular mechanism driving reverse development, and what happens to the animal’s nerve net during this process”.
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References/Sources/Materials provided by:
https://www.uib.no/en/michaelsarscentre/173833/young-again-study-shows-comb-jellies-can-age-reverse
https://www.sciencealert.com/wild-discovery-reveals-that-comb-jellies-can-age-in-reverse
