Division of Biosphere Science

Base for Field Science

Staff Information

Takashi Dempo
Field Science Center for Northern Biosphere
Aquatic Biology
Sub Course:
Assistant Professor
Toya Lake Station
denboh[at]fsc.hokudai.ac.jp ([at]->@)
The family Closteriaceae has been divided into one rather large genus Closterium with more than 88 species (each comprising one to several varieties) and the other monospecific genus Spinoclosterium. All members of this family are unicellular. Most species of Closterium are lunate-shaped while some are spindle- or needle-shaped like C. navicula or C. aciculare. Since they usually lack prominent morphological characters on their cell wall, such simple cells could not be readily discriminated with fixed samples among many closely related species in contrast to most species of the family Desmidiaceae with warts, spines, and radiating protuberances on their cell wall. Recently, we, desmidologist, can utilize their molecular information to re-classify them correctly with living samples although their culture strains are not easily available. As is seen for species of the other desmids, three types have also been found in the reproductive mode of Closterium: homothallism, heterothallism, and parthenogenesis. It is well known that their morphological divergence such as cell size and form has often occurred within some closely related species along with their evolutionary patterns of reproductive types. However, we hold a different view in determining whether we should deal with each population with different reproductive type as an identical species or not. In our laboratory, we collect a lot of species of Closterium from almost all parts of Japan, isolate each single cell sterilely and culture them in culture tubes containing proper liquid medium. After identifying them from their morphological characters, we investigate their reproductive type and genetic information to re-classify them correctly. Like some pioneering studies by Coleman, we align rDNA sequences with reference to their RNA secondary structures, and also exploit another possible utility of RNA secondary structure models that may work as an evolutionary indicator for relationships between taxa for molecular physiology. The purpose of our study is to make clear phylogenetic relationships among the species and examine the modes of speciation along with evolutionary patterns of their mating systems and reproductive type in the Closteriaceae although few fossil records for Closterium except the Middle Devonian Paleoclosterium have been discovered.
Evolutional biology, Plankton, Algae, Microbe, Field work, Labo work, Freshwater, Wetland, Phylogenetic systematics

Graduate School of Environmental Sceince / Faculty of Env. Earth Science, Hokkaido University