Famous participants in the toughman contests included
“Butterbean” Esch – a 350 lb. boxer with one punch and an iron jaw, and of
course, who can forget Mr. T. The contests are still held in many states, but
MMA now has the majority of the fan base, even more than traditional boxing
between trained fighters.
These guys were tough, but were they the toughest? Humans as
a rule are weak for their size, scared of more things than they should be, and
less inclined to fight to the death for a morsel of food or potential mate –
well most are. So…..
Questions of the Day:
What is the world’s toughest animal?
Ask a hundred people and you may get a hundred different answers.
The bull elephant can fight off an entire pride of lions and can lift five
tons. But can you really give the prize to an animals that is scared of a
mouse?! Maybe they aren’t afraid of
mice, but they will avoid them if possible, according to one of the more scientifically consistent episodes of Mythbusters.
A good second choice might be the honey badger. It
supposedly knows no fear, and proves it by depriving lions of the prey they
just killed. In one case, three honey badgers stole a entire carcass from seven
lions! The South Africa National defense calls their armored personnel vehicles
ratels, the afrikaans word for honey
badger.
The water bear is more scientifically known as a tardigrade (latin for slow walker), a phylum that falls
somewhere near arthropods and nematode worms. There are two classes
(eutardigradia and heterotardigradia) and more than 900 species, but there may be some overlap in those descriptions.
The adult tardigrade will have 40,000 cells, and will never
have more. What is more, every
species of tardigrade is matures with a specific number. This is called eutely (eu = good, and telos =
end). Many lower organisms may be eutelic; their cells have a limited number of
divisions, so they grow to that number and then stop.
It isn’t just whole organisms that might be eutelic, organs
can be as well. For example, the nematode Ascaris
ALWAYS has 162 neurons. The research model nematode C. elegans has exactly 959 somatic cells, although a 2011 study has
shown that C. elegans can lose
critical cell nuclei as they age – tell me about it. Other nematodes, rotifers,
and gastrotrichs have also been shown to have cell constancy at the body and/or
organ level.
Tardigrades do grow after they reach adulthood, just not by
adding cells. Growth by additional cells is called hyperplasia (excess formation), while growth by existing cells
becoming larger is called hypertrophy (excess
nourishment).
Different tardigrade species are adapted to nearly every
environment on Earth. They live in the Arctic and the Antarctic, in the
mountains and the oceans, in the deserts and the jungles. All are found near
water, some marine and some limnal
(freshwater), some in the water and some just next to the water held in mosses
or lichens.
But wherever you find them, you’ll find them in great
numbers. The density of tardigrades can approach two million per square meter. Yellow
crazy ants (Anoplolepis gracilipes) form
supercolonies of incredible density, yet they can only muster about 2000
individuals per square meter. Haven’t heard of crazy ants? You will – look them
up.
Tardigrade toughness doesn’t come from their pursuit of prey or
their ability to fend off predators, but their willingness to live in
conditions that would kill anything else, and
I mean anything, else.
Cold, not a problem. Tardigrades can have liquid nitrogen
(-346˚F/-210˚C) poured on them and they’re just fine. Heat – boil them for a
couple of hours and then watch them lay eggs and go back to eating. Radiation
isn’t a problem either; they can take 5700 grays of ionizing radiation without
blinking.... well, they could if they had eyes. Humans curl up in a ball and die
when exposed to 5 gray.
How do they manage these amazing feats? Basically – they die
and then come back to life. Technically, it’s called cryptobiosis (hidden life), but death and self-resurrection is not a
bad description. During cryptobiosis, metabolism is reduced by 1000x fold or
even more, down to the level where there is NO detectable chemical activity.
There are five recognized types of cryptobiosis, based on
the noxious environmental condition that triggers it – anhydrobiosis (without water), chemobiosis
(chemicals), cryobiosis (cold), anoxybiosis (lack of oxygen), and osmobiosis (change in osmotic
potential).
The primary form for tardigrades is anhydrobiosis. They drop
their claws, retract their legs and roll up into a ball called a tun. 99% loss
of water, roll up into “tun” this is important because it regulates the rate of
evaporative water loss. At this level, they don't hold enough water for damaging reactions
to take place or even enough water to form ice crystals. The water is replaced
by a sugar called trehalose.
Trehalose production is similar to the way many organisms
can protect their structures and biochemistry from environmental damage, but apparently scientists have just touched the surface of how tardigrades react to uncomfortable
environments. A 2013 study indicates that there are many unidentified organic
molecules present in the tuns of tardigrades that are not present in the
organisms under normal physiologic situations.
Earlier reports had professed that 120 year old tardigrades
were revived from dried lichen and moss samples in the British Museum, and that
decades old samples were just fine. But Dr. James Garey of the University of South
Florida tells me that many of these reports have been called into question and
cannot be repeated.
Dr. Garey’s estimate is that tardigrades can survive 1-5
years as a tun, with decreasing viability upon hydration after that. Still,
could any other animal you know of be dead for five years, with no air, no
water, high radiation, liquid nitrogen, and taunts about their size and lineage
– and then come right back to life when the opportunity is right?
Cryptobiosis is quite different than dormancy. Dormancy
doesn’t bring a huge change in physiology – like 99% dessication. Also,
dormancy is preemptive while cryptobiosis is reactive. However, a very good 2011 review of tardigrade reactions shows that they can undergo both dormancy and crytobiosis
– sometime simultaneously!
The question is – how do they survive the bad conditions
WHILE they are forming the tun? It takes about 20 minutes for tun formation to
occur, so it appears that many of the conditions they can endure require them
to already be in the cryptobiologic
state. They can survive the radiation when
they are dessicated, they can survive boiling when they are dessicated. I don’t think it makes them any less
amazing.
Can the exploits of this microanimal help humanity? You
betcha. Tardigrades' ability to undergo anhydrobiosis has begun to influence
the design of medicines. In third world countries, a lack of reliable
refrigeration requires vaccines and medicines don’t need
refrigeration, and can be reactivated upon ingestion.
Dry vaccines are
a current goal, so the National Institutes of Health recently put out a call for proposals for research into more thermostable and reactivateable
preparations. A late 2012 paper has identified a tablet form for deliver of
some protein drugs, with reactivation of the molecules with saliva. This would
be much better than the current reliance on hypodermics and refrigeration. So
tardigrades are tough for themselves, and may fight for us as well.
Borde, A., Ekman, A., Holmgren, J., & Larsson, A. (2012). Effect of protein release rates from tablet formulations on the immune response after sublingual immunization European Journal of Pharmaceutical Sciences, 47 (4), 695-700 DOI: 10.1016/j.ejps.2012.08.014
McGee, M., Weber, D., Day, N., Vitelli, C., Crippen, D., Herndon, L., Hall, D., & Melov, S. (2011). Loss of intestinal nuclei and intestinal integrity in aging C. elegans Aging Cell, 10 (4), 699-710 DOI: 10.1111/j.1474-9726.2011.00713.x
Guidetti, R., Altiero, T., & Rebecchi, L. (2011). On dormancy strategies in tardigrades Journal of Insect Physiology, 57 (5), 567-576 DOI: 10.1016/j.jinsphys.2011.03.003
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