HMN 2026: How Tardigrades reveal extreme heat-blocking survival trick while in tun state

Tardigrades, also known as water bears or moss piglets, are tiny eight-legged animals that can survive in extreme environments, where humans and most other animals would die. This resistance to extreme conditions, including intense heat, very high or low temperatures, radiation and low oxygen levels is called “extremotolerance.”

A biological process that allows tardigrades to survive in extreme environments is anhydrobiosis. This is a reversible process via which the animals lose most of their body water and their metabolism temporarily stops, which in turn allows them to survive in dry environments. When tardigrades undergo this process, they curl up and enter what is known as a “tun” state.

Researchers at the Indian Institute of Science recently carried out a study aimed at better understanding how a species of tardigrade—called Paramacrobiotus sp. BLR strain—survives extreme heat while in the tun state. Their findings, published in the Journal of the Royal Society Interface, suggest that reductions in thermal conductivity are central to the survival of this species at high temperatures and under extreme heat.

Measuring the flow of heat in tardigrades

To investigate the processes via which tardigrades Paramacrobiotus sp. survive while in the tun state, the researchers carried out a series of experiments. They placed active tardigrades and tardigrades in the tun state in small PCR tubes at extreme temperatures ranging from 45°C to 85°C, for a period of one hour.

While the animals were exposed to these high temperatures, they measured the flow of heat (i.e., thermal conductivity) in their bodies using an instrument they developed. They then compared both the survival rates and thermal conductivity of active tardigrades to those of dehydrated tardigrades.

“The objective of our paper was to find out the limit of thermotolerance of the tardigrade and its mechanism,” Sandeep M. Eswarappa, senior author of the paper, told Phys.org. “To do this, we built a vacuum apparatus to direct the heat flow through tardigrades. This helped us to estimate the heat transfer rates at two different states of tardigrades.”

Eswarappa and his colleagues found that active tardigrades did not survive high temperatures for one hour, even the lowest experimental temperature of 45°C. Instead, 90% of tardigrades in the tun state survived under the same conditions, and some of them were still alive after one hour at 85°C.

Interestingly, the researchers found that tardigrades in the tun state exhibited a higher thermal resistance and a reduced flow of heat through their bodies. In their paper, they propose that the observed lower thermal conductivity protects the animals’ internal cellular structures and prevents heat-related damage.

Toward a better understanding of extremotolerance

The results of this study suggest that the ability to survive extreme temperatures is supported not just by biochemical, but also by physical processes. Further research could try to validate the team’s observations across a wider range of extremotolerant animal species.

“Our observations suggest that tardigrades can adjust their thermal conductance to protect themselves from heat,” explained Eswarappa. “As part of our next studies, we plan to identify the molecular mechanisms behind this phenomenon.”

The findings gathered by Eswarappa and his colleagues could potentially also serve as inspiration for the design of new materials and technologies that can operate at extreme temperatures. These technologies could be deployed in space, deserts, underwater, areas affected by wildfires, and in other challenging scenarios.

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