The Seemingly Indestructible Jewels of Evolution
Introduction
Evolution is the mechanism through which the species of our world adapt to their surroundings. Traits that are deemed favorable, or those that positively contribute to the survival and reproduction of a species, are passed down, whereas those that disadvantageous are pushed out of their genome. In doing so, species evolve to best utilize the resources of their environment and fight against predators.
Water Bears?
Tardigrades have recently caught a lot of attention with some people calling them their “spirit animals.” In fact, tardigrades are the true jewels of evolution, embodying all that it can lead to. These somewhat cute extremophiles, nicknamed “water bears,” are seemingly indestructible. Tardigrades are found everywhere on earth, such as beaches, our backyards, all the way to peak of the Himalayan mountains, down the deepest parts of the oceans. However, these aren’t the only places where tardigrades can survive. Researchers have put these creatures to the most extreme tests and the water bears have passed all of them with flying colors. For example, in 2007 scientists sent a sample of tardigrades to space and exposed them to the vacuum of space for ten days. After returning to earth, around 67% of the sample were still alive. Not only were they able to survive in an environment lacking all the necessities of life, but also handled the destructive space radiation that would otherwise destroy any other organism.
Evolution and the Genome of Tardigrades
The unique evolutionary adaptations that the tardigrade has is its ability to enter a “tun” state through anhydrobiosis. The tardigrade enters this state when their environment completely lacks water, or is desiccated. Similar to its environment, the critter shrivels up into a ball-like shape while losing 97% of its water level and slowing its metabolism down to 0.01% of the normal level. Instead of the water in its system, a sugar molecule called trehalose, which is also found in other organisms like yeast that can survive drought, takes its place and helps stabilize the destructive expansion of water that would otherwise take place in extreme temperatures. In turning themselves to a dormant state, tardigrades can go into “hibernation” until conditions are favorable once again, perhaps a year, a decade, or even a century later.
Additionally, a recent analysis of the tardigrade’s genome revealed a hidden ability of these critters in their survival: to turn into glass. The analysis revealed that tardigrades have a specific protein that is unique to them, ironically called the “tardigrade-specific intrinsically disordered proteins,” or TDPs, that turn their cytoplasmic fluid into a glass-like state. TDPs are unlike most proteins in that in a normal environment with proper water levels, they do not have the concrete structure that most proteins have. In contrast, they are loose and free flowing. However, when faced with desiccation, the TDPs convert the cytoplasm into a glass-like substance. In doing so, this bioglass helps sustain other molecules that are sensitive to water levels. Additionally, TDPs help prevent water molecules from forming ice crystals that puncture the cytoplasm during freezing or drying, allowing tardigrades to survive in all conditions, even space.
The survival adaptations of tardigrades aren’t limited to their “tun” state and TDPs. The water bears have evolved to gain many tardigrade-specific genes that help in its survival. For example, a protein called Dsup binds to the tardigrades’ DNA and serves as a protective wall against radiation, preventing the DNA from denaturing and breaking apart. Combined with their copious amounts of anti-oxidant enzymes that neutralize ionizing radiation, tardigrades can reduce up to 40 to 60% of radiation damage. In circumstances where the DNA is damaged, the tardigrade genome contains more copies of a gene that helps repair DNA than any other organism as well.
Thieves?
It’s possible that the evolutionary adaptations of tardigrades could’ve been “stolen” from other organisms. To clarify, tardigrades have the ability to absorb the genome of foreign organisms through a process called horizontal gene transfer. However, this ability isn’t unique to tardigrades; bacteria have been known for years to achieve antibiotic resistance through horizontal gene transfer. However, distinctive to the tardigrades is the fact that up to 17.5% of their genome has been found to have its origins from other organisms. Following the process of anhydrobiosis, the cytoplasmic and nuclear membrane of the tardigrades become more porous than usual, allowing for the absorption of genetic material. As a result, many of the genes and adaptations of the tardigrades could have its origins from other organisms.
Applications and Conclusion
The study of tardigrades can lead to substantial applications in our lives. By taking advantage of the tardigrades’ preservation abilities, vaccines and other biological molecules could be infused with the water bears’ genome and be transported much easier. Additionally, this ability could be applied to food storage in third-world countries without access to refrigerators as well as for astronauts. Like the tardigrades may do, humans can also “steal” the tardigrades’ evolutionary abilities into helping our own cells fight radiation. In researching their resilience, interesting perspectives on aging and cancer could be found.
Ironically, despite their ability to survive in any environment, tardigrades can only continuously survive for a couple months. The creatures can break apart their lifespan into multiple decades, but ultimately, they are only active for a short period of time. Nature has a cruel way of balancing everything out and tardigrades are no exception.
To this day, how or why they evolved is still a mystery. The theories presented are some of the possibilities, but perhaps they are simply just aliens from space.
