Unusual “Time-Travel” Creature Can Age in Reverse, Astonishing Scientists

Under stressful conditions, the ctenophore Mnemiopsis leidyi can revert from a lobate adult stage to a cyddipid larva, depicted here. Credit: Joan J. Soto-Angel

Comb jellies can reverse their development from adult to larva, a rare flexibility in animal life cycles that may be an ancient trait.

A recent article in PNAS unveils a remarkable discovery: the ability for reverse development in a ctenophore, commonly known as a comb jelly. These findings indicate that life cycle flexibility in animals may be more widespread than previously believed, scitechdaily.com.

Animal life cycles typically follow a familiar pattern, declined in countless variations: they are born, grow, reproduce, and die, giving way to the next generation. Only a few species are able to deviate from this general principle, the best-known example being the ‘immortal jellyfish’ Turritopsis dohrnii, which can revert from an adult medusa back to a polyp. This elusive group of animals with flexible life cycles now includes the ctenophore Mnemiopsis leidyi.

“The work challenges our understanding of early animal development and body plans, opening new avenues for the study of life cycle plasticity and rejuvenation. 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 Joan J. Soto-Angel, a postdoctoral fellow in the Manet Team at the Department of Natural History at the University of Bergen.

Gelatinous time-travel

The remarkable discovery began by chance. While observing animals in the laboratory, Soto Angel noticed that an adult ctenophore had vanished from a tank, seemingly replaced by a larva. Curious to find out if these could be the same individual, he and Pawel Burkhardt, group leader at the Michael Sars Centre at the University of Bergen designed experiments to try and reproduce this potential reversion under controlled conditions.

When exposed to the stress of starvation and physical injury, Mnemiopsis leidyi demonstrated an extraordinary ability to shift from its lobate form back to a cydippid larval stage. “Witnessing how they slowly transition to a typical cydippid larva as if they were going back in time, was simply fascinating,” Soto Angel recalled. “Over several weeks, they not only reshaped their morphological features, but also had a completely different feeding behavior, typical of a cydippid larva.”

An ancient model to study life cycle evolution

The study broadens the known developmental flexibility of ctenophores and positions Mnemiopsis leidyi as a valuable model for future research in developmental biology and aging. Since ctenophores are among the earliest animal lineages, the findings suggest that 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.”

Reference: “Reverse development in the ctenophore Mnemiopsis leidyi” by Joan J. Soto-Angel and Pawel Burkhardt, 29 October 2024, Proceedings of the National Academy of Sciences.

DOI: 10.1073/pnas.2411499121