How tardigrades and other extremophiles adapt to alien environments
One of the most basic properties of life is that it can adapt to its environment. In fact, this is a key part of NASA’s working definition: Life is a self-sustaining chemical system capable of Darwinian evolution.. And the most powerful tool of adaptation used by any species is natural selection, the mechanism by which its genetic traits change over time.
The first form of life to arise on our planet, commonly referred to as LUCA (Last Universal Common Ancestor), was a fairly primitive microbe, but the organisms that followed have diversified wildly over billions of years. Natural selection has allowed life to inhabit almost every place on Earth, including several kilometers underground and the bottom of the oceans that cover most of the surface. The number of habitats, their varying degrees of complexity, and the ability of evolution to come up with creative ways to make an environment habitable is simply breathtaking.
Fish and invertebrates living in the deep ocean are clear examples of this adaptive ability. These creatures are often colorless. A lot of people don’t even have their eyes working, because who needs sight when you live thousands of feet below water where the sun never shines? Instead, deep-sea fish developed unusually large, razor-sharp teeth. If they happen to catch something in pitch darkness, they don’t want it to float away. To get an idea of the diversity of deep sea animals, check out the World Register of Deep Sea Species. (Creators star Wars probably thought of some of them when they imagined the extraterrestrial inhabitants of the ocean).
Deep-sea fish are a great example of adapting to difficult circumstances, but in my opinion, they are not even the most remarkable. Species that can survive in niches considered extreme (by human standards) are known as extremophiles. However, the term is vague because it is not always clear what we mean by “human standards”. Objectively speaking, one might even think of us like extremophiles, because we breathe oxygen, which is difficult to deal with due to the damage that radical oxygen compounds do to the body. For the first microbial inhabitants of the Earth, oxygen was a toxin. In fact, it caused a major mass extinction called the Great Oxidation Event about 2.4 billion years ago.
Usually, when scientists talk about extremophiles, they mean microbes that exist where no other life forms can exist. But some animals and plants can also be extremophiles. My favorite survivors from the plant kingdom are the resurrection plants, which, although they may look completely dead and decomposed, come back to life and resume photosynthesis after adding a few drops of water. They can lose up to 95 percent of their water content, but within 24 hours of repeated watering, they are fully photosynthetically active again and with little or no tissue damage. The near-death period can last quite a long time – Craterostigma can go without water for at least two years.
Even more impressive ramonda mikoni, also known as the Pyrenean violet, which not only can survive in cold habitats (most resurrection plants live in tropical or subtropical climates), but also has an average lifespan of 200 to 250 years! An article by Beatriz Fernandez-Marin from the University of the Basque Country in Spain details how the Pyrenean violet does this. While most resurrection plants accumulate sugar in response to extremely dry conditions, ramonda mikoni uses antioxidant compounds to trigger secondary metabolic reactions. Sugars help plants survive cold temperatures by protecting against osmotic stress and helping to stabilize cell membranes.
Tardigrades and mushrooms
My favorite animal kingdom survivors are the tardigrades, a group of species also known as water bears or moss piglets. Tardigrades can withstand temperatures from near absolute zero to 151°C.O Celsius, pressures ranging from vacuum to 6,000 times normal sea level pressure on Earth and radiation doses up to 5,000 Grays (1,000 times higher than any other known animal). They can also survive with little to no water. They do this by going into a dormant state called tun, during which almost all of the water in their bodies (which normally freezes and forms ice crystals at low temperatures) is replaced by sugar.
One of those mossy piglets Gipsibius Dujardini, it even turned out that it can withstand an acceleration of 16,000 g! In comparison, a constant force of 16 g can be lethal to humans.
Because of their amazing endurance, tardigrades have been suggested as likely candidates for “colonization” of other planets by terrestrial life forms. Although I’m not so sure. Moss piglets can survive interplanetary travel (do they even need a spaceship?), but only when they are at rest. When they wake up, they will need food – plants, algae, and small invertebrates – to survive. Most likely, if we decide to colonize other worlds, we will send microbes as the first interplanetary life forms from Earth.
In the kingdom of mushrooms, too, there are amazing adaptations. This is an incredibly diverse group of species, and every mycologist has a favorite. I have chosen here a bizarre family of macroscopic subterranean organisms known as Armillaria. Because it is pathogenic to trees, it is also known as honey mushroom or Armillaria root disease. These mushrooms are incredibly large. One genetically homogeneous colony found in Oregon measures almost ten square kilometers and is estimated to be between 1,900 and 8,650 years old. The total weight of the colony is about 600 tons, which means that if we consider it as a single organism, then it is the largest on Earth. (Personal note: although Armillaria one impressively huge mushroom, I’m much more of a yeast fanatic Saccharomycetes cerevisiaealso known as baker’s yeast, an indispensable ingredient for making bread and beer!)
Once again, the lesson to be learned from these bizarre creatures is that nature never ceases to amaze. And this is only on our familiar planet. Imagine the diversity we could find on alien worlds very different from ours in terms of their environmental conditions, such as in the deep ocean of Europa or on a super-Earth outside our solar system.
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