Phenotypic plasticity in hydrozoans: Morph reversibility

The life cycle of Hydrozoans typically comprises two phases: the polyp, eit her solitary or colonial with generally a benthic habitat, and the medusa w hich lives in the plankton. In its typical metagenetic cycle, the medusa is budded from the polyp, which is the product of sexual reproduction of medu sae. However several alternative reproduction patterns have also been descr ibed In particular some species are able to perform a regressive transforma tion of the medusae that transform themselves into polyps bypassing sexual reproduction. In a species with alternative morphs switched by the environm ent, the more labile is the correlation between environmental factors actin g on the genetic switch and the factors to which the resulting form is adap ted the more hazardous will be the development of either body form. However , we can explain the evolutionary advantage offered by reversion between mo rphs of these plastic species living in shallow water unpredictable environ ments: should produced medusae be released in the "wrong" environment, they would still have a chance of survival under another form.