Biogeographical differences in a common soil ciliate, Gonostomum affine (Stein), as revealed by morphological and RAPD-fingerprint analysis

Gonostomum affine is a common, hypotrichous soil ciliate showing a wide var iety of more or less distinct morphologies which, depending on the view, ca n be considered as taxonomic entities or variations of a single morphotype. Thus, we chose it as a model to investigate some main questions in ciliate alpha-taxonomy and biodiversity, viz., (i) the power of morphological meth ods and RAPD-fingerprints to separate two distinct morphospecies of Gonosto mum; (ii) whether morphology and RAPD agree in separating the most dissimil ar morphotypes; and (iii) whether G. affine has a biogeographical populatio n structure. Accordingly, we investigated one G. strenuum population from A ustralia and compared it with six G. affine populations from Europe, Africa , and South America. Data were analysed with classical similarity trees and two new methods combining morphological features and RAPD-fingerprints in single similarity trees. The main results of this study were: (i) Morpholog y could separate the two morphospecies very clearly, while RAPD could not, irrespective of the indices and clustering algorithms used; (ii) Morphotree s did not agree with RAPD-trees and not show a distinct biogeographical pat tern. However, a rather distinct biogeographical population structure becam e recognisable when morphological features and RAPD-fingerprints were combi ned in a single similarity tree, indicating (iii) a certain degree of geogr aphical uniqueness of various genotypes. Generally, however, separation was rather weak and highly dependent on the indices and clustering algorithms used, indicating that, at the present state of knowledge, most Gonostomum a ffine-like morphotypes fall into the range of natural variability of a sing le species.