Cyclomorphosis in Scenedesmus communis Hegew. Ecomorph expression at low temperature

Abstract

The study of Scenedesmus phenotypic plasticity was extended by examining a supposedly stable S. communis. The organism was grown in two-media at both 10 and 22°C; at 10°C, the growth rates were considerably lower. Surprisingly, during log growth at 10°C S. communis developed arcuate, multispined, eight-celled colonies, organisms with spines at the poles of middle cells, rather than typical four-celled, four-spined colonies. Also at that temperature, the ordered sequence of development of several forms, from multispined to acaudate ecomorphs, was observed. Each ecomorph, produced at a particular stage of growth, is a developmental form in a cyclomorphosis. In both media at the low temperature, distinguishing characteristics for the species (i.e., the distinct morphology of terminal cells and the veil of wall material between cell apices) failed to develop. Cells were larger and four-celled colonies up to 3·5 × wider. The arcuate, multispined, 10°C colonies resembled previously described taxa, such as S. pannonicus Hortob. Certain subspecific taxa within that genus were initially reported from material collected when the water temperature was low. The taxon S. communis, along with taxa in other species, must be placed in synonymy with an organism such as S. pannonicus, S. longus Meyen or S. maximus (W. et G. S. West) R. Chod.