Tardigrades and anhydrobiosis
Tardigrades are aquatic animals – even if their terrestrial habitat is simply a thin film of water in moss or leaf litter. When water becomes unavailable, tardigrades enter anhydrobiosis – a reversible dormant state. They draw in their legs and retract their bodies to form a tun. When conditions become favourable, tardigrades rehydrate and carry on with their life processes unharmed.
Diagram notes
The diagram in the video uses abbreviations to label parts of the tardigrade’s body. Most deal with feeding and digestion.
mo (mouth)
st (stylet)
pb (pharyngeal bulb)
mg (midgut)
go (gonad)
Questions for discussion
Adaptations can be structural, physiological or behavioural. How would you classify anhydrobiosis?
What do you think triggers tardigrades to enter anhydrobiosis?
Why do you think they tuck in parts of their bodies as they form a tun?
Transcript
Voiceover
Cryptobiosis is a physiological state in which an organism’s metabolic activity is significantly reduced due to inhospitable environmental conditions.
One form of cryptobiosis is anhydrobiosis, which is Greek for ‘life without water’. Anhydrobiosis, like other forms of cryptobiosis, is reversible. The organism returns to full metabolic activity unharmed.
Tardigrades use anhydrobiosis to survive environmental stresses, including extreme temperatures and desiccation.
When tardigrades sense a decrease in external water, they begin to enter the dehydrated tun state – drawing in their legs and contracting their bodies to form a desiccated cyst. Metabolic activity becomes undetectable. When conditions become favourable, tardigrades rehydrate and carry on with their life processes.
Acknowledgements
Video (Movie S1) from “Halberg KA, Jørgensen A, Møbjerg N” (2013). Desiccation Tolerance in the Tardigrade Richtersius coronifer Relies on Muscle Mediated Structural Reorganization. Video released under CC BY 4.0
Tardigrade dehydration and rehydration diagram, adapted from work by Chiswick Cap. CC-BY-SA-4.0
