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.
A new study shows unprecedented ability for reverse development in ctenophores, which are also known as comb jellies.
The findings suggest that life cycle plasticity in animals might be more common than previously thought.
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.
Joan J Soto-Angel, a postdoctoral fellow in the Manet Team at the Department of Natural History at the University of Bergen, said: “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.”
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.
Soto-Angel said: “Witnessing how they slowly transition to a typical cydippid larva as if they were going back in time, was simply fascinating.
“Over several weeks, they not only reshaped their morphological features, but also had a completely different feeding behaviour, typical of a cydippid larva.”
The study broadens the known developmental flexibility of ctenophores and positions Mnemiopsis leidyi as a valuable model for future research in developmental biology and ageing.
Since ctenophores are among the earliest animal lineages, the findings suggest that reverse development may represent an ancient feature in the animal kingdom.
Burkhardt said: “This is a very exciting time for us. 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”.
The new article is published in PNAS.
