Metabolic Dormancy in Aquatic Invertebrates

Abstract

One major approach used by invertebrates for coping with extreme environmental conditions is to enter states of metabolic and developmental dormancy. The possession of a latent or resting stage is a common occurrence in the life cycle of organisms inhabiting inconsistent or ephemeral environments, and this phenomenon has been a source of long-standing speculation and fascination (cf. van Leeuwenhoek 1702). Considering the remarkable habitat diversity that exists among aquatic invertebrates, it is not surprising that the distribution of dormancy is broadly scattered phylogenetically. Resting stages have now been reported in virtually every major phylum of invertebrates, with the notable exception of Echinodermata. In some taxa, mature adult forms have the ability to enter states of rest, while in others, specialized resting forms are common only during earlier stages of life cycles.

We sat beside the little pool and watched the tree-frogs and the horsehair worms and the water-skaters, and had wondered how they got there, so far from water. It seemed to us that life in every form is incipiently everywhere waiting for a chance to take root and start reproducing; eggs, spores, seeds, bacilli — everywhere. Let a raindrop fall and it is crowded with the waiting life ….. And we, seeing the desert country, the hot waterless expanse, and knowing how far away the nearest water must be, say with a kind of disbelief, “How did they get clear here, these little animals?” And until we can attack with our poor blunt weapon of reason that causal process and reduce it, we do not quite believe in the horsehair worms….. From Sea of Cortez. John Steinbeck and Edward Ricketts, 1941