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 similarity between genotypes from different waters did not show a significant relationship with the geographical distance among habitats, although genotypes isolated from the same habitat showed a higher genetic similarity than genotypes isolated from different habitats. Phylogenetic analyses of RAPD patterns 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 gene pool. The high genetic diversity observed is explained by a frequent occurrence of conjugation in the studied populations.