Genetic diversity in populations of a freshwater ciliate

RAPD fingerprinting with nine different primers revealed that all of 18 E. aediculatus isolates from nine ponds and streams in western Germany, France and the U.S.A. were genetically different. The extent of genetic similarit y between genotypes from different waters did not show a significant relati onship with the geographical distance among habitats, although genotypes is olated from the same habitat showed a higher genetic similarity than genoty pes isolated from different habitats. Phylogenetic analyses of RAPD pattern s indicate a separation of E. aediculatus strains into subgroups within one species, but all strains were genetically more similar to one another than to strains from two other Euplotes species. Crossings of the different E. aediculatus strains revealed they belonged to seven mating types of one gen e pool. The high genetic diversity observed is explained by a frequent occu rrence of conjugation in the studied populations.