Dormancy in invertebrates

The ability to survive in a dormant state is a widespread, yet unevenly distributed feature among invertebrates. Organisms belonging to classes and phyla that include fresh-water or terrestrial representatives are more likely to possess a dormant stage than those in groups that are exclusively marine. Moreover, within taxa where dormancy has evolved, it is more common among fresh-water and terrestrial species than in marine species. This correlation between dormancy and habitat across 29 free-living invertebrate phyla raises the question of cause and effect. Are dormant stages more common in fresh-water and terrestrial habitats because there is greater selection for dormancy in those environments, or is dormancy a prerequisite for the successful invasion of non-marine systems? The mechanism of dormancy varies among species and ranges from a specialized diapausing embryo to a quiescent adult. Dormancy has most likely arisen multiple times in invertebrate life histories, both within and between phyla. Although dormancy may facilitate the invasion of fresh-water and terrestrial habitats, it is not always a requirement: many non-marine species do not exhibit dormancy.