Notes on colony formation in Diatoma tenuis and Diatoma vulgaris
Colony formation in Diatoma tenuis and Diatoma vulgaris represent extensive topics and will only be briefly discussed here. Publications have been submitted on this subject.
Diatoma tenuis
Diatoma tenuis can occur in the form of longer chains and star-shaped structures, with up to four such
     |
star-shaped structures connected. Transitional forms also appear. In culture, only star-shaped and linked star-shaped colonies were observed. On the left again images from the cultures are shown.
A simple star-shaped colony of three diatoms does not seem to differ from Asterionella formosa with respect to the connection points at first sight, but with two connected stars it becomes clear that the connection points of the diatoms in the chains are not generally located at the same apex (see image below). The two diatoms that connect the two star-shaped structures each have their connections at diagonally opposite locations. The rules of formation must take this into account and allow the typical forms of simple and chained stars to reproduce themselves repeatedly.
For the preservation of the structures over the generations, the breaking of the chains must also take place appropriately. It almost always occurs spontaneously without external forces and exclusively at the connection points of the star-shaped substructures, so that star-shaped fragments are always formed.
|
|
Transitional forms arise between completed concatenated star-like structures. At the top of the page two examples of such forms are shown.In the example on the left, two separations are required for the almost fully developed diatoms to form a colony of two star-shaped structures. In the example on the right, there is just one. In the phase of exponential growth, the proportion of transitional forms is low, which can be explained by sufficient synchronicity of the divisions.
The video on the left shows the vegetative reproduction in a low-density culture in 3600 time-lapse.
The asymptotically reached angles between adjacent diatoms range around 120° and do not scatter by far as much as in Asterionella formosa. This high symmetry gives them a low sinking speed despite the small number of diatoms in the star. The influence of the asymmetry on the sinking speed can be roughly estimated. Furthermore, it is essential that the opening of the angles happens quickly compared to the generation time, so that favorable conditions exist for a longer time.
A study of pattern formation in Diatoma tenuis, including the timing of colony formation, was submitted under the title " Colony and Pattern Formation in Diatoma tenuis " for the following book:
Chain Diatoms [DCHN, Volume in the series: Diatoms: Biology & Applications, series editors: Richard Gordon & Joseph Seckbach, in preparation]” Tiffany, M. and Ghobara, M. (eds.) (2024).
Diatoma vulgaris
The image gallery of Diatoma vulgaris shown again below left exhibits long zig-zag shaped colonies. The connection points are located at changing positions of the diatoms. The discoverer of the species, Bory de Saint-Vincent (see his drawing right below) wrote that he could not recognize an order structure in it.
      |
 |
Nevertheless, it is possible to find rules for the structure formation, which, however, also have a stochastic part.
Agreement with a deterministic approximation is found only over lengths in the order of 20 to 30 diatoms. Further limiting the observability of the deterministic approximation are deviations from the synchronicity of the cell divisions.
The opening of diatoms after division into a V-shaped structure begins with a sudden opening, as in all observed species that form zig-zag or star-shaped chains. An example of a chain in dividing is shown on the left in 4500x time-lapse.
If you are interested in these investigations, I would like to refer you to the following publication:
"Pattern Formation in Diatoma vulgaris Colonies: Observations and Description by a Lindenmayer-System",
submitted for:
The Mathematical Biology of Diatoms [DMTH, Volume in the series: Diatoms: Biology& Applications, series editors: Richard Gordon & Joseph Seckbach, in press]. J.L. Pappas and R. Gordon, (eds.) Wiley-Scrivener, Beverly, Massachusetts, USA. (2023)
If you have any questions about these topics, please contact me.