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:
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:
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 (email@example.com).
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