Hot Link: the bearonauts are back!
Between September 14th and 26th 2007, a group of water bears travelled as space passengers.
Please follow the thrilling adventure at the up-to-date Bearonaut Blogspot by K. Ingemar Jönsson,
The project "Tardigrades in Space" (TARDIS) is a part of the Biopan-6 research platform
of the European Space Agency (ESA). Within the FOTON-M3 mission a russion rocket
took care to safely transport the tardigrades into space and to take them back to planet Terra.
Our readers will already know the well-balanced participating ethnic groups:
Richtersius coronifer, Milnesium tardigradum, Echiniscus testudo and
DNA investigations are foreseen to clarify in how far the tardigrade dry states ("tuns")
might have been damaged during the unprotected exposure to space conditions.
In competition with the Red Indian Summer: Colourful Tardigrades
The red and tawny gold colours of automn - we like them though we suspect that
the inbuilt beauty might be just a further picturesque coincidence
in a long series of mother nature's everyday brute decay and breakdown scenarios.
Also the tardigrades exhibit splendid shades of colours which are most conspicuous
when investigated in air. Normally we do not notice them as we use to look at
tardigrades in thin films of water. The reasons for water immersion are quite evident.
Our microscopes are optimized for thin sharp focus object slices
lying under cover glasses of a precisely defined thickness. Moreover,
the inner structures and anatomy of the tardigrades become visible only
when watched in liquid media. In water we do note how tightly the tardigrade
dry states, the so-called tuns, are packed around their stiff bucchal structures,
the bucchal tube and the stylets:
of an Echiniscus tardigrade, immediately after immersion in water.
It becomes quite clear that the maximum package concentration is restricted
by the non-bendable bucchal tube.
Image width ca. 0.15 mm.
The investigation in air is a little bit more cumbersome.
The dry moss cushions resemble miniature jungles and normally
most of the tardigrade tuns are perfectly hidden within the densely packed moss leafs:
Dry moss cushion. Photograph
in air. Image width ca. 1 cm.
But when dissecting moss cushions and when carefully screening
single moss plant stems we will come across tuns as well.
Separated single moss
plant from a dry moss cushion with a tardigrade tun.
Image width ca. 3 mm. Photographed in air.
The visible colour of the tardigrade tuns depends to a great extent
on the kind of illumination. The following photomicrographs illustrate that
the same kind of tun might appear dark, almost black, silver-white,
reddish-transparent, intensively blue, blue-red, even like mother of pearl,
in all rainbow colours.
All photomicrographs were made by means of white light.
The various colours are mainly due to interference phenomena.
Just remember school physics with the lessons about the colour of extremely thin platelets.
Incident light is being reflected on the upper and lower borderlines of
the platelet structures and the two light rays are producing interference when coming back to
the observer at different times due to pathway differences.
The same effect happens when thin oil or bacteria films on water are observed by means
of a torch. Depending on the angle we will observe different colours:
blue, green and red. The blue colour appears at high angles (small pathway differences),
the red one at low angles (greater pathway differences).
Area variations with different interference patterns signalize variations in the structural properties.
The pores of the Echiniscus armour plates do cause a complicated interference pattern
similar to the dots on a computer cd. Platelet structures with a typical thickness range between
0.25 to 0.5 µm as a rule will produce the strongest interference colours, whereas too small
and too big structures will produce no interference at all. Things become
more complicated due to overlay factors like different refractive indices
of the materials and different light incidence values.
The exuviae (empty cuticulas with eggs) of the Eutardigrade water bears
are less conspicuous than those of the Echiniscidae and reveal less colour.
This no-or-little-colour visual appearance is caused by the extreme smoothness
and the low wall thickness of the cuticula of the non-armoured Eutardigrades.
But also in those cases we will normally note a little bit of colour due to
interferences, similar to those effects that we find on modern florist's flower packaging material:
Exuvium of the Eutardigrade Milnesium tardigradum .
Three eggs in an early stage of development. The cuticula shows some
minute traces of colour, only at the edges. The pathway of the light is
longest there and allows some interference.
Those faint and almost invisible thin cuticula layers of the Eutardigrades
allow a much better insight into the tardigrade anatomy and egg development.
We will make use of this lucid biology window in our next issue in order to follow
the hatching of Milnesium tardigrades.
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).
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.