Tardigrades are aquatic organisms known to withstand some of the most extreme conditions on Earth and beyond. Now, new research suggests the hardy microscopic invertebrates may be vulnerable to long-term exposure to rapidly increasing temperatures associated with climate change.
Also known as moss piglets or water bears, tardigrades exhibit an extraordinary tolerance to extreme environments when they are dehydrated, or in a desiccated state. As an aquatic species, the millimeter-long organism needs to be surrounded in a film of water during its active state when feeding or reproducing. But when extreme conditions arise, tardigrades can enter cryptobiosis, a “reversible ametabolic state” whereby the organism essentially contracts its body, retracts its legs, and rearranges its internal organs to dry itself out.
Cryptobiosis allows the organism to combat environments that lack oxygen, have high levels of toxic concentrations, or see extreme temperature shifts. Yet, previous studies suggest that extremely high temperatures over a long period of time may be the tardigrade’s “Achilles heel.” With over 1,300 species described so far (including one that looks like a very extra glittery snake), some tardigrades can tolerate temperatures of 151°C (304°F) for up to 30 minutes. However, exposure to temperatures higher than 80°C (176°F) for any longer results in high mortality and almost all die at temps above 103°C (217°F).
"From this study, we can conclude that active tardigrades are vulnerable to high temperatures, though it seems that these critters would be able to acclimatize to increasing temperatures in their natural habitat,” said study author Ricardo Neves in a statement. “Desiccated tardigrades are much more resilient and can endure temperatures much higher than those endured by active tardigrades. However, exposure-time is clearly a limiting factor that constrains their tolerance to high temperatures."
It may be that high temperatures destabilize proteins that are essential for the tardigrades’ cryptobiotic survival. While this state of extreme dormancy allows for metabolism to come to a reversible stop, it requires the tardigrades to retain their “structural integrity.” The genetic makeup of tardigrades makes them nearly indestructible and capable of surviving aquatic environments around the world, including parking lots and Antarctica. A few thousand dehydrated tardigrades even wound up on the moon. However, it appears that extreme heat can alter this maintenance, particularly when a tardigrade does not have time to acclimate to its new environment.
“Global warming is already having harmful effects on habitats worldwide and it is therefore important to gain an understanding of how rising temperatures may affect extant animals,” write the authors in Scientific Reports.
The researchers conclude that the characterization of tardigrade genomes could help “provide important new perspectives on how tolerance to high temperatures is achieved.”