The world in general is pretty amazing and I think as adults we sometimes loose sight of this. Life just kicks us in the ass at some point and, for some of us, that curiosity and amazement flickers out. In a past show I alluded to this in a rant about how people might be a little happier in day to day life if they would stop worrying about the sudden stop at the end and just appreciate how amazing our little blue/green ball is.
In the spirit of that rant I’ve decided to start a new weekly post called, quite simply, “Amazing”. I’ll be detailing things I look at with that forgotten childlike wonder and question incessantly while my brain simply says “cool!”. Man-made, natural, earthbound and stellar…there’s plenty of amazing stuff out there to talk about. Hopefully some of these things will appeal to you in the same fashion.
For my first “Amazing” post I’ve dragged out one of my favorite animals: Tardigrades!
Strange is this little animal, because of its exceptional and strange morphology and because it closely resembles a bear en miniature. That is the reason why I decided to call it little water bear.
– J.A.E. Goeze (Pastor at St. Blasii, Quedlinburg, Germany), 1773
~ Basics ~
Tardigrades (a.k.a water bears or moss piglets) are microscopic animals that, at first glance, look similar to arthropods. They’re bilaterally symmetrical (the same on both sides) with 3 sets of legs on each side and tiny eyes. Their diminutive size (up to 1.5mm in length) means they have no need for a circulatory or respiratory system but they do have a tiny nervous system, relatively large brains, muscles, an outer cuticle (which they molt as they grow) and tend to be brightly colored. They walk on their legs with a gait not unlike a bear (see video at the very bottom of this post) and some species have clawed appendages. Though somewhat similar to arthropods they do not have segmented bodies, jointed legs or compound eyes. Recent DNA and RNA testing has also linked them closely to velvet worms but the tardigrades have their own phylum (tardigrada) due to several amazing and unique features.
~ Habitat & Survival ~
Water bears have been found literally everywhere we’ve looked for them. Mountaintops, extreme ocean depths, volcanic vents, under 5 meters of ice, cracks on a sidewalk…literally everywhere. If you were to walk outside right now and find a bit of moss or greenery there’s a good chance you’d find a tardigrade. While they can survive in nearly every condition on earth (and in space) they’re not considered extremophiles, rather extremotolerants (as they cannot thrive in the extreme conditions, just survive them). Forget cockroaches, these little guys are natures born survivors. To date, we’ve found they can and survive:
- freezing, then boiling, then freezing (repeat as nessciary)
- stable temperatures as low as -328F and as high as 304F (only for a few minutes)
- complete lack of water and oxygen (for up to 10 years, though, one was recovered from dried 120 year old moss in a museum only to die a few minutes later)
- extreme changes in salinity
- boiling alcohol
- an extended stay in outer space
- up to 6x the pressure of the deepest parts of the ocean
- submersion in some noxious chemicals
- enough radiation to kill any other living thing (570,000 rads of x-ray radiation)
- being placed in a vacuum and bombarded with electrons (they’re the only animal to survive having it’s picture taken with a scanning electron microscope)
How do they manage? While different species have different survivability rates, they all drop their metabolism to .01% of normal function (a cryptobiotic state; basically dead) and replace the water in their cellular walls with a sugar called trehalose. Some species also curl into a ball, known as a ‘tun’, until re-hydrated.
~ Diet & Reproduction ~
Using two sharp, needle-like, stylets they puncture the cellular wall of their meal and suck the fluids out though their mouth (pharynx). While most species feed on mosses and alge, some are carnivorous, eating other microbes (including other water bears!). While most species have males and females there are a few cases where only females have been found. In these cases reproduction is assumed to be asexual but, due to geographic diversity, males of those species aren’t out of the question. Within the gonochoristic (male and female bearing) species the females tend to lay eggs within a shed cuticula to later be fertilzed by one or more males. When hatched they can be as small as .1mm but resemble adults morphologically. As water bears grow they have been found to show clear signs of aging, making the old and young easily identified by the trained eye.
~ Evolution and History ~
Their size and structure makes tardigrade fossils extremely unlikely and equally unlikely to detect. The only recorded fossil specimens are from Cambrian-era deposits in Siberia and Cretaceous amber found in New Jersey and Canada. Whereas the amber specimens are extremely similar to living tardigrades, the Siberian fossils proved quite different, suggesting a stem group of living species.
Awesome video of a water bear trolling around some moss
There’s a lot more to learn about these amazing little creatures. The following links are a good start:
references & resources: