Heat shock as inducer of metamorphosis in marine invertebrates.

In most sessile marine invertebrates, metamorphosis is dependent on environmental cues. Here we report that heat stress is capable of inducing metamorphosis in the hydroid Hydractinia echinata. The onset of heat-induced metamorphosis is correlated with the appearance of heat-shock proteins. Larvae treated with the metamorphosis-inducing agents Cs+ or NH4+ also synthesize heat-shock proteins. In heat-shocked larvae, the internal NH4+-concentration increases. This fits the hypothesis that methylation plays a central role in control of metamorphosis. In the tunicate Ciona intestinalis, a heat shock is able to induce metamorphosis too.