The Biological Bulletin, Vol 190, Issue 3 302-312, Copyright © 1996 by Marine Biological Laboratory

DEVELOPMENT AND REPRODUCTION

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

S. Piraino, F. Boero, B. Aeschbach and V. Schmid
Istituto Sperimentale Talassografico CNR "A. Cerruti," Via Roma 3, I-74100 Taranto,and Laboratorio di Ecologia de1 Benthos, Stazione Zoologica di Napoli "A. Dohm, " 80077 Ischia Porto (Naples), Italy

Organisms develop through a series of stages leading to sexually mature adults. In a few cases ontogeny reversal is possible, but it does not occur typically after the onset of sexual reproduction. All stages of the medusa Turritopsis nutricula, from newly liberated to fully mature individuals, can transform back into colonial hydroids, either directly or through a resting period, thus escaping death and achieving potential immortality. This is the first metazoan known to revert to a colonial, juvenile morph after having achieved sexual maturity in a solitary stage. Selective excision experiments show that the transformation of medusae into polyps occurs only if differentiated cells of the exumbrellar epidermis and part of the gastrovascular system are present, revealing a transformation potential unparalleled in the animal kingdom.