How to become a Bio-Daredevil
Become a Tardigrade. That's my answer.
Yep, you read that right.
There is one organism on our planet, who is so resilient that not even five mass extinctions could kill it. I just told you what it is, but what IS it? Today, you'll find out what they are, how they function and are so damn tolerant to this planet as well as how we can use this in the future.
What is it?
A tardigrade is an eight-legged micro-animal that populates almost all environments on this planet. It's known as a water bear to some and looks kinda cuddly to me. Although, it does have a chitin exoskeleton which it outgrows and sheds - maybe not as cuddly as perceived. This helps people like me and you identify it as an Ecdysozoan (includes the arthropods and the nematodes too).
How did they come about though? They are thought to have diversified from their basal ancestors in the vibrant Cambrian period (500 mya). So if you think about it, they have been virtually unchanged for half a billion years. Crazy, right?
Resilience is Key
Tardigrades are probably the most resilient animals on this planet (that we know of) and this bodes quite well for them.
What I want you to do, is think of any habitat in the world, anywhere at all.
There are tardigrades there.
A pretty radical mind reading trick you can show to your friends, but it's not even a trick. It's true. Tardigrades are found on mountains, the deep sea, rainforests, volcanoes, Antarctica. This allows them to develop resistance to some of the harshest temperatures, pressures, hypoxia, radiation (as seen in a study in 2006) and even dehydration. But, you will see later how the heck they can pull off these stunts.
Here are some mind-bending resilience statistics for you:
pressures of 1200 atm
surviving more than 10 year dry states - body water capacity decrease by 82%
5000 Gy (gamma rays)
Repairing its DNA under strong UV conditions
What this says to me is that they can survive conditions and factors that limit and restrict most if not all life as we know it.
One thing I want you to remember, is that tardigrades are not extremophiles! They are only adapted to endure such harsh environments, not exploit them.
In fact, this has brilliant ecological impacts; if tardigrades can inhabit almost any environment on Earth, then surely that means that a lot more organisms than just tardigrades are capable of this?
Let's simulate this shall we?
tardigrade populates environment extensively
attracts predators (parasitic protozoa, spiders, neamtodes and other tardigrades)
forms an ecosystem in that particular environment
I was thinking this could be modelled with the Lotka-Volterra model (a pair of non-linear differential equations that describe predator-prey interactions in an ecosystem) - BUT, if we use this, we have got to assume the following:
The prey population finds ample food at all times.
The food supply of the predator population depends entirely on the size of the prey population.
The rate of change of population is proportional to its size.
During the process, the environment does not change in favour of one species, and genetic adaptation is inconsequential.
Predators have limitless appetite.
And this only works if the prey has an unlimited supply of food - AHA! That's where we remember that tardigrades are not extremophiles and therefore cannot exploit, only endure their environment.
"While tardigrades can survive in extreme environments, they are not considered extremophiles because they are not adapted to live in these conditions. Their chances of dying increase the longer they are exposed to the extreme environment."
So on that basis, we cannot apply Lotka Volterra models (as they assume they are indeed extremophiles) and hence tardigrades cannot create huge or even smaller ecosystems wherever they end up - they may seem cool, but in reality, they just need a hug!
How do they do it?
They do it through a process called cryptobiosis, which is defined as 'a metabolic state of life entered by an organism in response to adverse environmental conditions'
But if you cast your minds to the different types of hazards tardigrades can resist:
extreme temperatures and pressures
Well, our little friend here utilises different versions of cryptobiosis specialised for each adversity - anhydrobiosis, cryobiosis, anoxybiosis.
'Anton van Leeuwenhoek first documented cryptobiosis in 1702, when he observed tiny animalcules in sediment collected from house roofs. He dried them out, added water, and found that the animals began moving around again. The animals were likely nematodes or rotifers, other types of cryptobiotic animals.'
What they do, is they curl up into a tiny ball called a 'Tun'. It requires the formation of a protective sugar called trehalose which moves into its cells and replaces lost water, by forming a preserved matrix. It prevents crystallisation of cells and hence prevents damage to the cell surface membrane (which controls many key cell functionalities and for example, charge balance).
Another mesmerising mechanism they are believed to have adopted is the utilisation of Tardigrade Specific Intrinsically Disordered Proteins (TDP's), whereby these proteins become a glassy structure when the cells start to dry out, cocooning any elements of these cells that are vulnerable to dehydration for example.
“When the animal completely desiccates, the TDPs vitrify, turning the cytoplasmic fluid of cells into glass,”
says Thomas Boothby of the University of North Carolina at Chapel Hill.
“We think this glassy mixture is trapping [other] desiccation-sensitive proteins and other biological molecules and locking them in place, physically preventing them from unfolding, breaking apart or aggregating together,” - this basically freezes the tardigrade in time until conditions improve again, ready to resume where it left off!
This has been known to reduce metabolism in a single tardigrade to 0.01%, extending its survival of such crazy crazy environments.
But there has been some heated debate as to whether horizontal gene transfer (HGT) can or cannot occur in tardigrades. HGT is the movement of genetic material between individual unicellular or multicellular organisms; it plays a key role in evolution.
One paper in 2015 proved HGT, but another in 2016 attempted to disprove it - not enough research here and so we can't really make a definitive decision right now!
In 2015, they stated that 17.5% of it's genome was foreign - 'They found the H. dujardini genome is material from several entirely different kingdoms—mostly bacterial (16 percent) but also fungal (0.7 percent), plant (0.5 percent), archaeal (0.1 percent), and viral (0.1 percent).'
If it could exchange genes in this way, then HGT coupled with it's ability to reproduce asexually could provide quite integral insights into the fact that organisms that are stress-tolerant 'might be predisposed to acquiring foreign genes'. Horizontal gene transfer (HGT) causes the exchange of specific genes in the genome which could tend to more resiliant organisms than others, because they possess that one gene the other tardigrades are jealous of. This forms the basis of Evolution by Natural Selection where allele frequency of a selective advantage is increased in a population - that advantage being tolerance to stressful environments in this case.
This allows us to think about the 'tree of life, but more as a web of life' - where the branches can intersect now...
Why should you care?
You don't need to really.
If you are mugged on the street (hopefully you aren't), then tardigrades aren't really going to help you in that situation. Ah, but if you want to preserve yourself, only to be thawed back to reality in the future to discover a whole new world, then maybe, just maybe this could work.
Cryopreservation is a far-fetched idea in my books and doesn't seem to have worked in the past. But what if we employ some of the tardigrade's mechanisms for our own benefit? Okay, we can't Cryopreserve, but we could resist certain environments better.
So what I'm saying, is that even if we do manage to utilise trehalose or another substance in the future for cryopreservation or to resist different environments to larger extents, then maybe we don't even need it - maybe it's just a case of natural exposure.
Some may argue that that comes with Natural Selection (Darwinian) and some Lamarckian side of thinking to some extent in the fact that natural exposure allows you to become more tolerant. Just how Arctic Inuit communities are better suited for the cold than your average Indian man from Mumbai (not me) who lives in 30 degrees Celcius of heat everyday.
But you see, that's the problem, one could argue that we don't occupy extreme environments compared to something that tardigrades can tolerate - so what's the point?
What are some questions we could answer in the future by applying our knowledge of tardigrades to our own lifes:
Maybe preserve specimens for longer periods of time than previously anticipated?
Are there any commercial benefits to substances such as trahalose (preservation)?
As you can see, I'm adding a lot of maybe's and questions to this article, because we need to keep asking these questions and not settle for the knowledge we have right now. If we settle now, then society collapses and the progression of humankind stops.
I think there's a lot of scope for research here as to what needs to be done to allow us to adapt to this ever-changing environment - it may not seem like it, but I kid you not, the Earth is changing as we speak and has been doing so for a while now (4.6 billion years - not that long).
Remember what I said at the start, tardigrades have survived all 5 mass extinctions. What I want you to think about is how we can use tardigrades to our own advantage to survive the imminent mass extinction we should all be doing something about...
I think as a species, it is our job to thrive here (which we have done) and continuously seek ways to improve our way of life and the Earth's aswell, because ultimately we can just do the same thing over and over again for millions of years - treat the Earth unfairly.
But if we all actively seek ways to improve life for yourself and others, then collectively we can make a difference. I'm going into the Earth Sciences as a career, but you don't have to - just be mindful of your actions and think what impact it could have on a small and large scale.
Because at the end of the day, we are all in this together, like the Covid -19 lockdowns - we are all Earth Scientists in the end.
So Aryan, how do you become a Bio- daredevil?
Become a tardigrade.
Yes you did read that correctly - that's my answer.
Radiation tolerance in the Tardigrade Milnasium Tardigradum - https://www.researchgate.net/profile/Takahiro_Kikawada/publication/6620865_Radiation_tolerance_in_the_tardigrade_Milnesium_tardigradum/links/547fc19e0cf25b80dd703913/Radiation-tolerance-in-the-tardigrade-Milnesium-tardigradum.pdf (accessed 24/1/21)
What is a tardigrade - https://serc.carleton.edu/microbelife/topics/tardigrade/index.html (accessed 2/2/21)
What the World's Toughest Animal Is Really Made Of - https://www.nationalgeographic.com/news/2015/11/151128-animals-tardigrades-water-bears-science-dna/ (accessed 3/2/21)
No evidence for extensive horizontal gene transfer in the genome of the tardigrade Hypsibius dujardini - https://www.pnas.org/content/113/18/5053 (accessed 1/2/21)
Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade - https://www.pnas.org/content/112/52/15976 (accessed 1/2/21)
Tardigrade - https://en.wikipedia.org/wiki/Tardigrade (accessed 22/1/21)
Tardigrades turn into glass to survive complete dehydration -
https://www.newscientist.com/article/2124893-tardigrades-turn-into-glass-to-survive-complete-dehydration/#ixzz6lSXZuPiC (accessed 3/2/21)