LOCAL AND TEMPORAL DISTRIBUTION OF DIFFERENT GENOTYPES OF POND-DWELLING STENTOR COERULEUS

DNA fingerprints of 721 individuals of the freshwater ciliate Stenter coeruleus revealed a heterogeneous local distribution of four genotype s of this species. Different genotypes dominated in seven ponds locate d 0.1-400 km apart; none of the detected genotypes were detected in al l of the ponds. Identities of the relative genotype frequencies in the pond populations varied from 0.00 to 0.99. These values did not corre late to the geographical distance between ponds. Several comparisons o f populations showed very high genetic identity (0.99) associated with the largest geographic distance (400 km). The data suggest no strong isolation of populations, but rather relatively high levels of gene fl ow among several populations. In one pond, significant temporal change s in the relative genotype frequencies accompanied a decrease in the S tenter abundance during the summer of 1996. For one genotype, the chan ges were reversed until spring of 1997, in the others they were not. D ivergent seasonal selection factors may cause such reversible shifts, but chance effects may underlie non-reversed frequency changes.