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What are they doing in winter?

In fact, this is not a modern question. R. Sydney Harper, member of the famous British Royal Microscopical Society has been thinking about this topic already half a century ago and has left a report for us:

"A few month ago the water in the bird-bath was teeming with these organisms, and then a frost came and the water was frozen solid. On thawing, I examined the water again, and found that these little animals were still alive and active".
[many thanks to B. Krause, U.K., for the literature hint]

From this we do have an answer already. Everything goes on in winter. Tardigrades apparently have no problem with a little bit of body-freeze and body re-thawing.
The consequence for us microcopy amateurs is that we can go on watching tardigrades also in winter. Just go ahead and try in a real snow scenario (to international readers: we hope that there is a little bit of snow in your country from time to time as well)

[ snow and moss ]

Urban moss on pavement in winter.
Sorry, the tardigrades are not visible here due to the image scale.


There are further reasons why tardigrades have to be tough guys (and girls). We have already heard about the process of drying out and coming back to life. Furthermore there are moulting phases which each tardigrade undergoes about ten times in life.

Sometimes we would like to moult as well: problems at home, problems at work, being "consulted" or treated unjustly - but of course humans are not able to move on to another skin.

In contrary the tardigrades are able to moult, leaving their old skin (*) in a similar manner as snails do. One reason for moulting is that the so-called cuticula of the tardigrades is unable to grow with the tardigrade. It has been found out already in the first half of the 20th century that the tardigrades might use moulting as a skin cleaning process as well: any parasite living at the outside of the skin is left alone with the old skin.

The beginning of the moulting process can be recognized by the somewhat erratic movements. The tardigrades are unable to feed in this phase and do not clinge to their plant substrate as usual.

[ Tardigrade (tardigrada) during moulting ]

Tardigrade during moulting. The old skin is clearly visible. Body length ca. 300 µm.

[ Tardigrade (tardigrada) during moulting ]

Tardigrade during moulting. Close-up of the head with double contours caused by the separation of the old and the new skin.
Typical  Macrobiotus tardigrade.

The tardigrades have to do a lot of exercise in order to loosen the old muscle-skin joints.

[ Tardigrade (tardigrada) during moulting ]

Tardigrade during moulting. Even in the still images the task is quite clear and the style of movements can be deducted. Body length ca. 300 µm.

The old cuticula can be clear like glass, reminds of cellophane foil, is completely unflexible and has a tendency to crease.

[ Tardigrade (tardigrada) during moulting ]

Tardigrade (tardigrada) during moulting.
Hind body. Old and new claws of the fourth pair of legs are visible at the same time.
Typical Macrobiotus claws.

[ Tardigrade (tardigrada) during moulting  ]

Tardigrade (tardigrada) during moulting.
Head: Cellophane type structure of the old skin.

The animal is moving very dynimcally.
Top left: stylets visible.

In the next issue we will follow the further steps of moulting. Lust but not least we will see that the old cuticula bears some interesting visual information. And we have not to bother the tardigrade in order to study those details.

(*) Skin in this context is meant as "Cuticula" i.e. the outermost layer of a more complex system made up of several systems.


R. Sydney Harper: The Tardigrada. The Microscope, 9 (1952) Heft 3 (Sept./Okt.).

© 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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