Aging in reverse: Comb jellies can transform from adult to juvenile 

A recent study has revealed the extraordinary capacity for reverse development in the ctenophore, or comb jelly, specifically in the species Mnemiopsis leidyi. Comb jellies seem to use the strategy of aging in reverse as a survival strategy when they are under pressure.

This surprising discovery, led by the University of Bergen, has added fresh perspectives to the field of developmental biology, suggesting that life cycle plasticity might be more prevalent in the animal kingdom than previously assumed.

Traditionally, animal life cycles follow a well-established sequence: birth, growth, reproduction, and death. Only a few exceptions defy this pattern, such as the “immortal jellyfish” Turritopsis dohrnii, known for its ability to revert from an adult medusa to a polyp stage. 

Now, this remarkable club of life-cycle-reversing organisms includes the comb jelly Mnemiopsis leidyi, adding a new chapter to what is understood about animal regeneration and development.

Life cycle plasticity and rejuvenation

The discovery happened by chance during routine laboratory observations. Joan J. Soto-Angel, a postdoctoral fellow at the University of Bergen, first noticed an adult Mnemiopsis that seemingly morphed into a larval form. 

“The work challenges our understanding of early animal development and body plans, opening new avenues for the study of life cycle plasticity and rejuvenation,” he said. “Witnessing how they slowly transition to a typical cydippid larva as if they were going back in time, was simply fascinating.”

Intrigued by this unexpected transformation, Soto-Angel, together with Pawel Burkhardt from the Michael Sars Center at the University of Bergen, conducted controlled experiments to test whether this reversion could be consistently triggered. 

Comb jellies aging in reverse

Under conditions of stress, such as starvation and physical injury, the Mnemiopsis displayed an ability to revert from its lobate adult form to a juvenile-like cydippid stage. 

Over several weeks, the specimens not only shifted their physical characteristics but also adopted feeding behaviors typical of the larval stage. 

This ability to transform fundamentally alters the way scientists understand life cycle stages and development in early animal lineages.

Implications for regeneration research

The implications of these findings reach beyond ctenophores themselves. “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,” Soto-Angel noted. 

Ctenophores are among the earliest diverging animal lineages, so this newly discovered plasticity could represent an ancestral trait retained from early evolutionary history.

“This fascinating finding will open the door for many important discoveries,” Burkhardt added. “It will be interesting to reveal the molecular mechanism driving reverse development, and what happens to the animal’s nerve net during this process.” 

Understanding how nerve structures adapt or are preserved during such drastic transitions could provide insights relevant to neurobiology and regenerative medicine.

Aging in reverse for survival

Reverse development might have evolved as an adaptive survival strategy, allowing organisms to respond to environmental challenges by resetting to a simpler developmental stage. 

The reversion observed in Mnemiopsis leidyi under stressful conditions could be an evolved mechanism to increase resilience, conserving resources until conditions improve.

The new evidence prompts questions regarding how these mechanisms are regulated and whether similar processes could be found in other species, particularly in more complex organisms. 

The ability of comb jellies to revert to a juvenile form could carry implications for how scientists approach the study of aging, cellular repair, and tissue regeneration.

New horizons in developmental biology

The discovery paves the way for future research into developmental flexibility and regeneration. Revealing the molecular mechanisms that facilitate this reverse development will be key to understanding not just ctenophores but potentially broader biological processes.

The findings challenge previously held notions that complex life cycles are irreversible, showing that under certain conditions, some species can alter their developmental trajectory. 

This opens new questions about how widespread such capabilities may be and whether they exist, undiscovered, in other branches of the animal kingdom.

In conclusion, this breakthrough in studying Mnemiopsis leidyi has added a significant piece to the puzzle of evolutionary biology, demonstrating that the potential for life cycle reversal and developmental plasticity could be more common than once believed. 

The research not only provides new insights into early animal evolution but also presents exciting opportunities for studying regeneration, aging, and cellular processes in broader biological contexts.

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