Reverse Development in Jellyfish: Raising New Questions About Aging

• 30 Nov 2024

Reverse Development in Jellyfish: Raising New Questions About Aging

 

It's not the first time scientists have stumbled upon a remarkable marine phenomenon by accident. The case of the "immortal jellyfish" is one such example. Discovered by Christian Sommer and Giorgio Bavestrello in the 1980s, this jellyfish, Turritopsis dohrnii, stunned researchers when they found that it could revert to an earlier stage of its life cycle instead of dying when stressed.

 

Normally, adult jellyfish, known as medusae, release free-swimming larvae called planulae. These larvae then settle to form polyps, which, in turn, generate new medusae. But Sommer and Bavestrello observed a bizarre process where stressed medusae reversed their development, essentially turning back into an earlier life stage — similar to a butterfly transforming back into a caterpillar.

 

This phenomenon, known as reverse development, has now been observed in another marine creature, the comb jelly Mnemiopsis leidyi. Scientists in Norway have found that, like the "immortal" jellyfish, these comb jellies can also revert to an earlier, larval form when stressed.

 

While the term "immortal" is often used to describe Turritopsis dohrnii, it's somewhat misleading. "Reverse development" is a more accurate description, according to Pawel Burkhardt, an evolutionary neuroscientist at the Michael Sars Centre, University of Bergen, Norway. Burkhardt, along with his colleague Joan Soto-Angel, led the study of Mnemiopsis leidyi.

 

In their research, the scientists subjected the comb jellies to two forms of stress: prolonged starvation and physical injury, specifically "lobectomy," where the adult lobes are cut off. Both stressors were followed by a reduced feeding regime. They discovered that lobectomy led to lower mortality and higher rates of reversion, with 40% of the lobectomized jellies fully reverting to a larval stage. In contrast, only 14% of the starved jellies reverted.

 

"The unique aspect of Mnemiopsis is that a single individual can revert to a single larva," Burkhardt explained. This is different from Turritopsis dohrnii, which reverts to a colony of polyps, making it harder for scientists to track the development of individual specimens.

 

These findings have significant implications. According to Ferdinando Boero, a marine biologist not involved in the study, the discovery broadens our understanding of reverse development, showing that it can occur in non-cnidarians like Mnemiopsis leidyi. This suggests that the ability to reverse development may not be limited to just one group of jellies, but could be present in species with different body structures and evolutionary histories.

 

Although both Turritopsis dohrnii and Mnemiopsis leidyi are categorized as "jellies," they belong to distinct biological groups: Turritopsis is a cnidarian, while Mnemiopsis is a ctenophore. Their structural differences — or body plans — suggest that reverse development may take on different forms depending on the organism.

 

 

Could humans do reverse development?

 

Could this process have any relevance to human aging? While some scientists have explored the implications of Turritopsis dohrnii's regenerative abilities for human biology, much less is known about how Mnemiopsis leidyi’s reverse development could apply to humans. Burkhardt and his team are focused on understanding how the nervous system changes between the larval and adult stages of the comb jelly. This process involves the regeneration of structures such as tentacles, which require a specific nervous system to function.

 

"The next few years will be critical to understanding the genetic processes behind this," Burkhardt said. "If a genetic switch exists that can restart development, we might look into whether it can be applied to human cells."

However, as Boero points out, while this research is fascinating, rejuvenating humans via reverse development seems unlikely due to our low biological plasticity. The complexity of the mechanisms at play means that reversing aging in humans may remain out of reach, for now.

 

Nevertheless, these discoveries continue to inspire scientists to explore the mysterious process of reverse development in the animal kingdom, pushing the boundaries of what we know about life cycles, survival strategies, and the potential for regeneration in nature.