Sexual reproduction: where and when?

In desmids in general, sexual reproduction is a rather rare phenomenon, at least in Europe. However, there are great differences between the various species. For instance, in the saccoderm desmid Cylindrocystis brebissonii conjugation may be regularly observed. Presumably this has to do, among other things, with the high cell densities in which Cylindrocystis species use to occur. For as motility of desmid gametes is most limited, the chance on mating is higher according as potential partner cells are closer together.

Dense cell suspension of Cylindrocystis brebissonii

Mating, conjugation and zygospore formation in Cylindrocystis brebissonii

Also Closterium kuetzingii  and Micrasterias papillifera are some of the species in which zygospore formation is relatively often recorded. 

Zygospore of Closterium setaceum (a relative of Cl. kuetzingii)

Zygospore of Micrasterias papillifera

However, of the vast majority of desmid species zygospores are only very incidentally reported or even quite unknown. For example, of Micrasterias truncata, by far the most common Micrasterias species in Europe, there is only one single record (Homfeld 1929).

Obviously, species-specific sexual potential is genetically determined. Apart from the fact that for conjugation often the simultaneous presence of physiologically different + and – cells is required, presumably in many species sexual potential in general is degenerated (Coesel 1974, Coesel & Teixeira 1974). Possibly this has to do with the environmental conditions under which most desmids use to flourish, i.e. peaty habitats that seldom or never dry out completely. In such an environment desmid cells may easily survive in vegetative state. Sexual reproduction, involving genetic recombination and attended by the formation of thick-walled, resistant zygospores, on the contrary, is particularly functional in instable habitats like wetlands that dry out thoroughly and for a lengthened time.

In this connection it is significant that European clones of Closterium ehrenbergii isolated from pools on clayey or sandy bottoms periodically drying out exhibited mating behaviour where clones of that same species isolated from peaty habitats could not be induced to any sexual activity (Coesel 1989). But even the fertility of the first mentioned group of European clones appeared strongly reduced as compared with that of many (sub)tropical strains of that same morphospecies (Coesel 1988, Ichimura et al. 1997).

(Partly) abortive conjugation
between English clones of
Closterium ehrenbergii

A great deal of the (sub)tropical clones of Closterium ehrenbergii were isolated from paddy fields, known to dry out periodically.There are indications that zygospore formation in desmids in (sub)tropical regions is less rare than in temperate/boreal regions, maybe because of a greater difference between wet and dry seasons (Handke 1996).


The process of sexual reproduction


Homfeld, H., 1929. Beitrag zur Kenntnis der Desmidiaceen Nordwestdeutschlands, besonders ihrer zygoten. — Pflanzenforschung 12: 1-96.

Coesel, P.F.M., 1974. Notes on sexual reproduction in desmids. I. Zygospore formation in nature. — Acta Bot. Neerl. 23: 361-368.

Coesel, P.F.M. & R.M.V. Teixeira, 1974. Notes on sexual reproduction in desmids. II. Experiences with conjugation experiments in uni-algal cultures.

Coesel, P.F.M., 1988. Biosystematic studies on the Closterium moniliferum / ehrenbergii complex in western Europe. II. Sexual compatibility. Phycologia 27: 421-424.

Coesel, P.F.M., 1989. Biosystematic studies on the Closterium moniliferum/ehrenbergii complex in western Europe. IV. Distributional aspects. — Cryptogamie, Algol. 10: 133-141.

Coesel, P.F.M., 1997. Matteola curvata (Nordst.) comb. nov., an interesting filamentous desmid from tropical America. — Algol. Studies 86: 11-16.

Handke, K., 1996. Zygosporen Saccodermer und Placodermer Desmidiaceen in Aufsammlungen der Jahre 1971-1995 aus Europa, Asien und Amerika. — Mitt. Inst. Allg. Bot. Hamburg 26: 5-129.

Ichimura, T., F. Kasai & P.F.M. Coesel, 1997. Geographical and ecological distribution of highly polyploid populations of the Closterium ehrenbergii species complex. Phycologia 36: 157-163.