Reduced ageing in the frozen state in the tardigrade Milnesium inceptum (Eutardigrada: Apochela)

Abstract

Tardigrades can survive harsh environmental conditions, such as drought and low temperature. To withstand freezing, they enter cryobiosis, a state of biological organization in which metabolic activity slows down or comes reversibly to a standstill. Thus, cryobiosis resembles anhydrobiosis, where tardigrades (and a few other invertebrate groups) undergo extreme desiccation and appear not to age in the dry state. The lack of ageing in the anhydrobiotic state, the so‐called ‘Sleeping Beauty’ hypothesis, is assumed also to pertain to cryobiosis, but this has not been investigated. To test this, a group of tardigrades was subjected to sub‐zero temperature treatment by alternating weekly periods of freezing at -30°C and feeding at 20°C. The temporarily frozen tardigrades lived twice as long as the control group, but both control and temporarily frozen groups had similar lifespans if the time spent frozen was excluded. This represents the first demonstration that the ‘Sleeping Beauty’ hypothesis applies to cryobiosis, meaning that tardigrades do not age while frozen.