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Eternal sleep? - a dry state with expiry date (II)

How long do you think that one of those torch dry cells will be able to provide some electricity?. One year, five years, fifty years? Thanks to Ebay we were able to purchase some very old dry cells recently and we think that we didn't come across those parrot color cells here for decades. Now, in 2008, they are still able to provide full torch illumination!

[  Old loupe with illumination by historic dry cells ] [  Old loupe with illumination by historic dry cells ]

Left side: Old loupe. Right side: Very old, presumably original dry cells, povided with the loupe, still working. Estimated age of the dry cells: three decades.

But, everyday practical experience teaches that such a dry cell can run out of energy much quicker, within a few years. Obviously, as our oldie dry cells above are able to prove, there are individual differences. And, of course, the iron plate shell will last much longer than the internal chemistry.

Tardigrades are much more complicated than those try cells but they consist of a long lasting shell as well which houses a more delicate and susceptible internal chemistry. So we can look out in our dry samples (I) for living tardigrades and (II) for remaining structures that are still existing but cannot be revived any more.

In the  November issue  we had discussed a thrilling article on tardigrade dry state length. Thanks to this article we did remember a dry moss sample which resided on top of our wardrobe for more than four years:

[  4 Jahre alte Moosprobe mit Bärtierchen ]

Moss sample from France, recovered in Summer 2002 and kept dry until 2006.

Of course we were eager to compare our Echiniscus revival results with those in the mentioned article. In short, the results were similar but not exactly the same. Obviously the survival capacity of the Echiniscus tardigrades is drastically reduced after four years (compared to revival experiments with fresh outdoor samples). In our first experiment we found hundreds of tardigrades which were immobile after rehydration and remained so. Even after moving the tardigrades to fresh oxygen rich water not a single water-bear came back to active life. But further identical experiments tought us that a very small minority of the tardigrades was not dead - even after those four years. Alltogether we found three Echiniscus tardigrades moving normally after 12 hours, two Eutardigrades (Ramazzottius oberhaeuseri) feeding normally and two Macrobiotus eggs which could be brought to hatching in the micro aquarium!
The percentage of living tardigrades was in fact very close to zero, far below one percent. But keep in mind that a tardigrade population might fully recover with a single female survivor outside.
The revival process in those rare cases appeared to be retardiated. Whereas normal tardigrade dry state "tuns" might come back as quickly as within five minutes after rehydration, our "old" tardigrades remained many, many hours in the  asphyctic (anoxybiotic)  state. With the Echiniscus tardigrades, even after 12 hours the snouts appeared to be still slightly retracted though the animals were moving and crawling in a perfectly normal manner:

[ tardigrade in the course of revival  ]

Echiniscus tardigrade, revived after four (!) years of permanent desiccation. Body length ca. 0.3 mm.

[ tardigrade in the course of revival ]

Same tardigrade as above, but other focus level. A remaining crease in the head region clearly indicates that the snout is still slightly retracted.

As far as the other moss inhabitants were concerned, we encountered different survival characteristics. We didn't come across living nematodes or amoeba but found myriads of living rotifers. After having witnessed some living tardigrades even after four years of desiccation we want to reach out for the extremes and will have a closer look on an dry moss herbarium dating back to 1925! See you.

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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