The taxonomy and evolution of theAssulina-Valkanoviacomplex were investigated in a spruce forest soil which included aSphagnumplot (GDR, Thuringia). In both habitatsAssulina muscorumoccurred in two colour forms (brown and colourless) and four shapes. A quantified phenospectrum fromAssulina muscorumwas obtained. The four shapes were distributed differently between the brown and the colourless forms inSphagnumand soil. The shell measurements showed statistically significant differences between the brown and the colourless forms. Even between the two brown populations there were some significant differences. Each of the four shape types of brown and of colourlessAssulinacan be kept in clonal cultures for some time. However, without selection, single cultures eventually revert to mixed types. The four shape types show different degrees of stability. These colour and shape forms are genotypes, which can also occur for short periods in the natural habitats. The brown populations inSphagnumand in the soil were dominated by different shape types during the period of investigation.Valkanovia eleganscannot be distinguished fromAssulina muscorumtype 4, butValkanoviacan inhabit both upper and lower soil horizons, whereasAssulinaand its forms lives exclusively in the upper horizon (litter).Valkanoviafrom the lower horizon is constant in clonal culture. The conclusion of the present investigation is that there are stable and unstable constellations within a changeable genome, which give asexual groups both a taxonomic structure and a continuum of forms. Selection can increase stability, by polygenic control of features.
展开▼
