Spatial Integration of Cellular Shapes in Green Microalgae with Complex Morphology, the Genus Micrasterias (Desmidiales, Zygnematophyceae)

Abstract

While ontogeny of multicellular organisms requires an interplay among tissues, morphogenesis of unicellular structures is typically organised with respect to differential growth of their cell covering. For example, shapes of various microalgae have often been emphasised as examples of symmetric fractal-like cellular morphology. Such a self-similar pattern is typical for the variability of a spatial fractal, with the shape variation remaining the same at different scales. This study investigated how these cells are integrated. A geometric morphometric analysis of spatial integration in the genus Micrasterias was used to assess the variation across scales by comparing the slopes of the linear fit of the log bending energy against the log variance of partial warps. Interestingly, the integration patterns were distinctly different from the notion of self-similarity. The variability consistently increased with decreasing scale, regardless of the cultivation temperature or the species examined. In addition, it was consistent after the adjustment of the slopes for the digitisation error. The developmental control over the final shape progressively declines with decreasing spatial scale, to the point that the terminal lobules are shaped almost independently of each other. These findings point to possible considerable differences in the generation of morphological complexity between free-living cells and multicellular organisms.