For those divers feeling their age on more arduous dives and wishing they could wind the clock back to their prime, don’t dismiss the possibility. It seems that at least some of the creatures seen on your dives are able to do just that, so imagine if their ability could be replicated!
Researchers Joan Soto-Angel and Pawel Burkhardt of the University of Bergen in Norway have discovered that a species of comb jelly, Mnemiopsis leidyi, has the ability to reverse its life-cycle, U-turning from adulthood to a larval stage. The bad news is that what is required to drive the process is severe stress.
In fact another species, Turritopsis dohrnii, was already known to be able to revert from adult medusa to a polyp, earning it the tag “immortal jellyfish”, but the new find demonstrates that this ability is not unique.
“We showed that mature lobate stages of M leidyi are able to reverse to a cydippid larval stage after a period of stress,” says Soto-Angel. “The fact that we have found a new species that uses this peculiar ‘time-travel machine’ raises fascinating questions about how widespread this capacity is across the animal tree of life.”
Unusual abilities
Comb jellies, or ctenophores, had previously been associated with regeneration and another unusual ability: to reproduce sexually even at the larval stage.
When Soto-Angel noticed that an adult M leidyi jelly, also known as a sea walnut, had vanished from a tank leaving only a larva behind, he and Burkhardt set out to find out whether they could control the conditions for such a reversion.
To achieve this, 65 healthy adult sea walnuts were kept isolated in tanks and starved for two weeks before being fed only once a week, and later every two days. Fifteen had had their adult lobes surgically removed, adding a further stress factor.
The jellies began to shrink, those still with lobes reabsorbing these into their bodies. “Witnessing how they slowly transition to a typical cydippid larva as if they were going back in time was simply fascinating,” says Soto-Angel.
“Over several weeks, they not only reshaped their morphological features, but also had a completely different feeding behaviour, typical of a cydippid larva.”
Ancient feature
The experiment showed that while seven of the 50 starved jellyfish fully reverted to larvae, a higher proportion of the lobectomised and therefore more-stressed jellies – six out of 15 – did so.
Comb jellies are among the earliest animal lineages, so it is thought that reverse development might represent an ancient feature of the animal kingdom.
“This fascinating finding will open the door for many important discoveries,” says Burkhardt. “It will be interesting to reveal the molecular mechanism driving reverse development, and what happens to the animal’s nerve net during this process.”
The study is published in the journal Proceedings of the National Academy of Sciences.
Also on Divernet: 5 jellyfish species you may see more often in UK’s warming seas, Warming & winds propel alien jellyfish to UK, Deep jelly named – no sample required
