Are jellyfish immortal?

Tamsin wants to know whether so-called immortal jellyfish really exist. Chris Smith put this question to ecologist Danni Green from Anglia Ruskin University...

Danni - Yeah, so it’s not immortal in the way that in the old movie, the Highlander is immortal. So obviously not chopping off their heads and absorbing their powers unfortunately. But yeah, there is a jellyfish called Turritopsis Dohrnii, and it was actually discovered by accident, by a lazy grad student who was doing some experiments on them over the summer. And his name was Christian Sommer, and he had the medusa in the tank, which is the jellyfish form we know and love, the adult form, with the bell and the tentacles. And he left them over the summer, and he went off on holiday. When he came back he expected to find some dead medusae, maybe some polyps. All he found was polyps, which is the juvenile form. That’s the form that sits on the bottom, and that eventually grows into smaller medusae. And they are sexually reproductive, and they reproduce planula larvae and they come back down into polyps again. And all he found was polyps and he thought “that’s strange, what’s happened, where are all the dead ones, where are all the different stages?”

So then they did some experiments and they discovered that what was happening, was that when these animals get stressed, they revert to a juvenile state. So it’s a little bit like the Benjamin Button of Cnidaria I guess. So they get stressed and they can go back into being a polyp, and they can do it forever as far as we know, in a laboratory system at least.

Chris - So they transform the body of the big one, the parent for want of a better phrase, into lots of little blebby off bits, which are the polyps.

Danni - Back into one, and it’s a little bit like a butterfly going back to a caterpillar. It’s a bit like that.

Chris - But it’s also re-absorbing and redeploying all its body parts to make a totally new form of the organism?

Danni - Yeah

Chris - And not just one, but many?

Danni - Yeah so, it’s a process called transdifferentiation. And apparently, there’s talk amongst medical scientists like yourself, to use this in a way for human health, and to reduce the aging process.

Chris - But if what you’re saying is true, that these animals can just basically turn themselves back into a more primitive form of themself, there will be some jellyfish cells in the adult that turn into juvenile jellyfish cells. But when those little ones grow into big ones again, they’re going to make new cells, aren’t they? So the cells that are in there, there might be the odd cell that’s from the original parent, but they’ll have grown to make lots of newer cells. Won’t they?

Danni - Yeah, exactly.

Chris - So is it strictly immortal then?

Danni - Well it’s immortal in the sense that it can just keep going, again and again, ultimately. Not in the sense that they can’t be killed.

Chris - But a human being can reproduce, Laura will know. And you take an egg cell, that an adult has made but actually was made when her mother was pregnant with her. And that egg is then fertilised by a sperm, that one cell. You then make a whole new organism. But at the same time you’ve still made all new cells, so, you could call a human immortal then, because it’s similar in a sense to what the jellyfish is doing isn’t it?

Danni - Yeah, I suppose technically, it’s not immortal, but it’s probably the closest thing that we have on Earth that we know of to immortal perhaps.

Chris - Why do you think the jellyfish do this? Is it some kind of defence mechanism?

Danni - I think it’s a defence mechanism, it’s preservation. Now, it’s not been observed in the wild, keep in mind, because obviously this is a difficult animal to study, it’s only been seen in the laboratory. And as far as we know it can just keep doing this over and over, and even if you pinch them with a pair of forceps, they can do this within three hours. They can reduce back from the medusa stage to the polyp stage. So it happens very quickly as well.