Study

Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa)

Piraino, Stefano; Boero, Ferdinando; Aeschbach, Brigitte; Schmid, Volker

The Biological Bulletin, 1996

Peer-reviewedcontrolled laboratory experimentlaboratory

What they did

Medusae of Turritopsis were subjected to starvation, temperature change and physical damage in culture, and their subsequent development was followed histologically to determine the fate of the tissues.

Studied in: Turritopsis
Sample size: medusae subjected to stress in culture

What they found

Stressed medusae contracted, settled and transformed back into the polyp stage, with differentiated cells changing type directly rather than passing through an undifferentiated intermediate. The resulting polyps went on to bud new medusae.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

The medusa stage can revert to the polyp stage by transdifferentiation, reversing what had been considered a one-way developmental sequence.

How NatureHQ reads it

This is the paper underneath "the immortal jellyfish", and the finding is stranger and narrower than the phrase. Nothing here is an animal that does not die: these medusae are eaten, they get sick, and the reversal is a stress response rather than a default. What was overturned is the assumption that development runs one way — an adult cell changing directly into a different adult cell type, in an animal, without going back to a stem-like state.

Limitations

Laboratory stress conditions; how often reversal happens in the sea is unknown.
The genus is taxonomically messy and later work has split it, so "Turritopsis nutricula" in this paper may not be the species usually named in popular coverage.
Reversal is not survival: predation and disease are unaffected by it.