Tardigrades (whose tiny cylindrical bodies are 0.01 to 1.2 millimeters long) are masters at adapting to extreme environmental conditions that would be deadly to most organisms on Earth. In the state of anhydrobiosis , that is, complete dehydration, they are capable of surviving for many years in a dormant state. Although it is something we already knew, all the secrets of these tiny invertebrates have not yet been revealed. For example, what happens to their biological clock when they go into a frozen state to survive sub-zero temperatures? Scientists claim to have found the answer to this question.
In 2019, Professor Ralph Schill of the University of Stuttgart showed that tardigrades can survive for many years in a state of anhydrobiosis and the same happens when frozen. However, do they age or not in state state? maybe this process is slower? Now, a team of researchers in Germany, including Ralph Schill himself, and South Korea have already found the answer: tardigrades do not age.
Stopping the biological clock
The scientists took a group of more than 500 tardigrades that were subjected to repeated cycles of freezing and thawing, until all the animals died. Meanwhile, another group of tardigrades was kept at normal room temperature.
When the researchers deducted the length of time the tardigrades spent in the frozen state, comparison with control groups showed nearly identical lifespans. “Tardigrades also freeze their biological clock in ice like a sleeping beauty,” Schill clarifies.
This is their best kept secret: when they are frozen, the so-called water bears go into a state of “cryobiosis” and stop aging completely until they thaw. Such a finding builds on previous research that showed tardigrades undergo a similar process called anhydrobiosis when faced with extremely dry conditions. This incredible ability to completely shut down her metabolism until circumstances become more favorable has been labeled the “Sleeping Beauty” hypothesis in reference to the fairytale princess who spends a century in suspended animation.
a similar life
Among those that were frozen (at -30ºC) and thawed continuously, the longest-lived tardigrade survived a total of 169 days, of which 75 were spent in cryobiosis while 94 were spent at normal temperature. Similarly, the oldest tardigrade in the control group lived for 93 days, illustrating how animals appear to stop aging altogether when frozen.
“During periods of inactivity, the internal clock stops and only starts working again once the organism reactivates,” explained Schill, in his new work published in the Journal of Zoology. “So tardigrades, which typically only live a few months with no rest periods, can live for many years or even decades.”
Referencia: J. Sieger et al, Reduced ageing in the frozen state in the tardigrade Milnesium inceptum (Eutardigrada: Apochela), Journal of Zoology (2022). DOI: 10.1111/jzo.13018
