• Emily Costello

How to live forever - Jellyfish edition

The gift of immortality. Living forever. It's something we read about in stories and see in the movies. Nothing like real life... or so we thought. Introducing Turritopsis dohrnii (aka. The Immortal Jellyfish).

Now, what has led to this teeny little floating piece of living jelly to earn such an impressive title?

For a normal jellyfish (Hydrozoa), their life begins as larvae, tiny specks floating in the vast ocean. Those that survive predation at this stage will eventually come to settle on hard ground and form young polyps - squishy living plant-like things if you will. This is the safest and most stable stage of their life as they are protected from predators and resilient to changes in their environment (remember this). As they grow, they will bud off into small jellyfish, released into the sea to grow and mature (they are now in the medusa form). Once fully grown, mature jellyfish will reproduce by releasing sperm and eggs into the water to produce larvae once more. The adults jellies will age and die. This is where their journey ends.

So what happens to Turritopsis dohrnii?

Essentially, it's the same cycle. However, these guys have the strange ability to revert into that polyp form whenever the hell they want! As mentioned before, this stage is the safest, so when they get stressed as fully grown adults, or even feel in danger, they will turn into a ball of tissue and grow as a polyp again on the rocks. Weird I know. Imagine if every time you got stressed you could just revert back to being a baby, where you have no worries and everyone did everything for you. Problem solved!

If you think about it, the ability to change forms is not uncommon. Caterpillars turn into butterflies and tadpoles into frogs, but they never go the other way. Trans-differentiation (the changing of one cell type to another) is something that nearly all living things are capable of. When a human baby is growing and forming, the cells are changing into specialised types. Every cell in our body has all the information it needs to grow a whole new person, however after it has become specialised to do a specific job, it only has access to part of that information (for example, a skin cell can grow more skin cells but cannot produce cells fit for the heart). This is why scientists are so interested in this particular jellyfish. Even though as an adult it is made up of specialised cells, it can collapse and revert to a ball of un-specialised cells over and over again.

Imagine what we could achieve with this knowledge. Being able to generate healthy tissue from damaged ones.. maybe even grow a lost leg!

As cool as the immortal jellyfish is, you might be wondering how our seas are not full to the brim with them if they can truly live forever. Well, the truth is, even the immortal jelly, with its' never ending life cycle can end up as a tasty snack if it is unlucky enough to cross paths with a hungry turtle :(

(Lisenkova, A., Grigorenko, A., Tyazhelova, T., Andreeva, T., Gusev, F., Manakhov, A., Goltsov, A., Piraino, S., Miglietta, M. and Rogaev, E., 2017. Complete mitochondrial genome and evolutionary analysis of Turritopsis dohrnii, the “immortal” jellyfish with a reversible life-cycle. Molecular Phylogenetics and Evolution, 107, pp.232-238)

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