Anhydrobiosis in tardigrades—the last decade

Journal of Insect Physiology 57 (2011) 567–576

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Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys

Review

On dormancy strategies in tardigrades
Roberto Guidetti *, Tiziana Altiero, Lorena Rebecchi
Department of Biology, University of Modena and Reggio Emilia, via Campi 213/D, 41125 Modena, Italy

A R T I C L E I N F O

A B S T R A C T

Article history: Received 29 November 2010 Received in revised form 2 March 2011 Accepted 3 March 2011 Available online 12 March 2011 Keywords: Anhydrobiosis Cryobiosis Encystment Cyclomorphosis Resting eggs Evolution Tardigrades

In this review we analyze the dormancy strategies of metazoans inhabiting ‘‘hostile to life’’ habitats, which have a strong impact on their ecology and in particular on the traits of their life history. Tardigrades are here considered a model animal, being aquatic organisms colonizing terrestrial habitats. Tardigrades evolved a large variety of dormant stages that can be ascribed to diapause (encystment, cyclomorphosis, resting eggs) and cryptobiosis (anhydrobiosis, cryobiosis, anoxibiosis). In tardigrades, diapause and cryptobiosis can occur separately or simultaneously, consequently the adoption of one adaptive strategy is not necessarily an alternative to the adoption of the other. Encystment and cyclomorphosis are characterized by seasonal cyclic changes in morphology and physiology of the animals. They share several common features and their evolution is strictly linked to the molting process. A bet-hedging strategy with different patterns of egg hatching time has been observed in a tardigrade species. Four categories of eggs have been identified: subitaneous, delayed-hatching, abortive and diapause resting eggs, which needs a stimulus to hatch (rehydration after a period of desiccation). Cryptobiotic tardigrades are able to withstand desiccation (anhydrobiosis) and freezing (cryobiosis) at any stage of their