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Dactylobiotus dispar (III)

A typical  Homo sapiens  needs about two decades for development, sometimes even more ... just think of those youngsters that are aged 30 and still live with their parents! Perhaps you happen to know this "Elling" cinema movie where the main character takes still more time and patience to develop.
As a rule the parental precautions tend to be more complex for complex beings, whereas "primitive" organisms like amoebas or paramecia seem to behave differently: at the very moment they are "born" by cell division they already appear to be perfectly able to feed and to develop like the parental organism.

There are controversial discussions in literature about whether tardigrades are in fact able to take care for and to protect their eggs after the moment of egg deposition. It has been reported that some species carry along their eggs within the old cuticula after moulting thus performing continuous and ongoing care also after egg deposition. Of course it might be difficult to decide whether this behaviour has to be interpreted as an "accident", as instinct or even as intelligent intention:

[ Tardigrade, carrying along the old cuticula with eggs ]

Some tardigrade species are known to carry along their eggs within the old cuticula after moulting. This kind of parental care can be continued until the hatching occurs.
Illustration based upon an original drawing by Ernst Marcus (1928), see literature, p. 185.

It took us a long time until we were able to document a situation in tardigrade life that can be definitely regarded as parental care. We found in a single case that a  Dactylobiotus dispar  female chose an appropriate shelter for its eggs that normally would be deposited freely, without a sheltering cuticula:

[ Dactylobiotus dispar, eggs in protective water flea shell ]

Eggs by Dactylobiotus dispar , deposited in a water flea shell. Diameter of the eggs ca. 90 µm. The egg in the lowest position on the image is already empty, the missing baby tardigrade hatched, gone and away.

Of course one could argue that this is a unique finding and that the deposition in the shell did occur by accident.
But a look into the scientific literture reveals that scientists have reported similar scenarios for other tardigrade individuals and other tardigrade species. E.g. Ernst Marcus in his famous tardigrade monograph depicts eggs of the tardigrade  Hypsibius hastatus  in a water flea shell as well and remarks that chitinious remains of insects can serve as tardigrade egg hides too, in this particular case referring to the species Macrobiotus pullari .
The sober tardigrade scientist in his constant fight for non-emotional scientific objectiveness will prefer to talk about a thigmotactic behaviour, i.e. about an egg deposition that might be purely mechanically triggered by some sort of material object, no matter what object.
On the other hand the amateur and tardigrade enthusiast will possibly believe that those findings must be interpreted undoubtedly as undeniable proofs for the tremendous intelligence of those tardigrade females that seem to be able to chose selectively among the many objects in water in order to provide an optimum shelter for their babies.
In any case, why not? We know that individuals of the  Homo sapiens  species are able to choose among various TV channels, advertised merchandise and a selection of restaurants ;-)


Marcus, E.: Bärtierchen (Tardigrada). p. 185 and p. 210/211. Jena 1928.

© 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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