Deciphering the Biological Enigma—Genomic Evolution Underlying Anhydrobiosis in the Phylum Tardigrada and the Chironomid Polypedilum vanderplanki

SIMPLE SUMMARY: Water is a requirement for life on Earth; loss of free water within the body or cell almost always leads to death. However, in several invertebrate lineages, some species can tolerate desiccation by entering an ametabolic state known as anhydrobiosis. Here, we review recent advances in our understanding of the molecular mechanisms and genomic evolution underpinning anhydrobiosis. We then propose several perspectives for further improving our understanding of anhydrobiosis. ABSTRACT: Anhydrobiosis, an ametabolic dehydrated state triggered by water loss, is observed in several invertebrate lineages. Anhydrobiotes revive when rehydrated, and seem not to suffer the ultimately lethal cell damage that results from severe loss of water in other organisms. Here, we review the biochemical and genomic evidence that has revealed the protectant molecules, repair systems, and maintenance pathways associated with anhydrobiosis. We then introduce two lineages in which anhydrobiosis has evolved independently: Tardigrada, where anhydrobiosis characterizes many species within the phylum, and the genus Polypedilum, where anhydrobiosis occurs in only two species. Finally, we discuss the complexity of the evolution of anhydrobiosis within invertebrates based on current knowledge, and propose perspectives to enhance the understanding of anhydrobiosis.