Cyclomorphosis in Scenedesmus subspicatus R. Chod. Cell Behavior During the Unicell-Colony Transformation of a Phenotypicly Plastic Organism

Abstract

An ordered sequence of ecomorph development, from a unicellular type to multi-spined colonies to acaudate forms, takes place over time in the spiny forms of Scenedesmus. This is the first report of two steps of such a sequence, the unicell-colony morphogenesis, in one strain of S. subspicatus. A detailed analysis of growth and morphology of UTEX 2532 at 10°C revealed that colonies were formed at that temperature and that cell mortality was occurring during this unicell-colony transformation. As the unicellular stage disappears and colonial ecomorphs develop within the population, a deflection in the growth curve has previously been noted, especially with S. armatus. Such deflections also occurred with S. subspicatus. At various stages of growth the developmental phenomena in these phenotypicly plastic microorganisms were indicative of the occurrence of a cyclomorphosis. Supporting data are derived from experiments conducted at both cold and warm incubation temperatures. Additionally, cold temperature induction of extra spines on individual ecomorphs takes place when the processes of cell adhesion and subsequent spine formation, closely coupled at warm incubation temperatures (standard conditions), become uncoupled at 10°C. These developmental steps take place while progeny are still within the parent wall. With all the morphological changes, organisms are able to adapt to the prevailing environmental conditions.