Tardigrades, also known as water bears, are remarkable creatures known for their ability to withstand extreme conditions. These tiny, eight-legged animals can be found in nearly all habitats on Earth, ranging from the deepest oceans to the highest mountains. They have evolved a unique survival mechanism called cryptobiosis, where they enter an inactive state known as a “tun state.” This ability allows them to halt their metabolism, enabling survival in the harshest environments, such as the vacuum of space or extreme temperatures.
Cryptobiosis and Tardigrade Survival
Cryptobiosis is a survival strategy where tardigrades almost completely stop their metabolic functions. This state helps them endure dehydration, extreme temperatures, and even space-like conditions. Scientists believe that this ability also played a role in helping tardigrades survive mass extinction events, such as the “Great Dying,” which occurred around 252 million years ago. During this event, approximately 90% of life on Earth was wiped out due to catastrophic environmental changes triggered by volcanic eruptions.
Recent Study on Tardigrade Fossils
In a study published on August 6 in Communications Biology, researchers reanalyzed ancient fossils of tardigrades encased in amber. These fossils are estimated to be between 72 million and 83 million years old and represent some of the first fossils of tardigrades ever discovered. By using advanced imaging techniques, such as confocal fluorescence microscopy, scientists were able to create high-resolution 3D images of the fossils and classify the extinct species.
Discovery of a New Tardigrade Species
Among the fossils studied, only one species had been previously named: Beorn leggi. The other fossil was too small to be described earlier. However, with the advanced imaging techniques, researchers identified and named a new genus and species of tardigrade, Aerobius dactylus. This discovery allowed scientists to trace the evolutionary history of tardigrades and gain insights into when they developed the ability to enter cryptobiosis.
Evolution of Cryptobiosis
Not all tardigrades can enter a tun state. There are two major classes of tardigrades, and only one family within these classes can undergo cryptobiosis. By studying fossil features, such as the shape and placement of tardigrade claws, researchers estimated that the two major classes of tardigrades diverged around 500 million years ago during the Cambrian period. Cryptobiosis is believed to have evolved separately in both classes between 430 million and 175 million years ago, encompassing several mass extinction events.
The Role of Cryptobiosis in Extinction Events
The researchers believe that cryptobiosis helped tardigrades survive mass extinctions, including the Great Dying. By entering a state of suspended animation, tardigrades could survive until environmental conditions improved. While this ability likely contributed to their survival during these catastrophic events, it is uncertain if cryptobiosis was the primary reason for their persistence throughout Earth’s history.
Multiple-Choice Questions (MCQs):
- What is cryptobiosis in tardigrades?
- a) A form of reproduction
- b) A state of extreme activity
- c) A survival mechanism where metabolism is nearly halted
- d) A way to enhance their growth
- Answer: c) A survival mechanism where metabolism is nearly halted
- What event is referred to as the “Great Dying”?
- a) The extinction of dinosaurs
- b) The Permian extinction around 252 million years ago
- c) The Ice Age
- d) The rise of mammals
- Answer: b) The Permian extinction around 252 million years ago
- Which imaging technique did scientists use to create 3D images of tardigrade fossils?
- a) X-ray
- b) Confocal fluorescence microscopy
- c) Electron microscopy
- d) Ultrasound
- Answer: b) Confocal fluorescence microscopy
- What does cryptobiosis help tardigrades survive?
- a) Extreme temperatures
- b) Dehydration
- c) The vacuum of space
- d) All of the above
- Answer: d) All of the above
- When did the two major classes of tardigrades diverge?
- a) Around 500 million years ago
- b) Around 300 million years ago
- c) Around 250 million years ago
- d) Around 100 million years ago
- Answer: a) Around 500 million years ago
- Which of the following statements about cryptobiosis is true?
- a) It was developed to survive the Great Dying.
- b) It likely helped tardigrades survive mass extinction events.
- c) All tardigrades can enter cryptobiosis.
- d) Cryptobiosis evolved only once in tardigrades.
- Answer: b) It likely helped tardigrades survive mass extinction events.