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Korpelainen, H. 1987. Reproductive strategies of Duphnia mugnu genotypes. —Hereditas 106: 181–188. Lund, Sweden. ISSN 0018–0661. Received May 26, 1986

During the almost three-year period of the investigation on Daphnia magna populations about 10% of the loci examined by electrophoresis showed sïgnificant differences in genotype frequencies between reproductive classes and sexes. Also, the intensity of reproduction varied greatly between genotypes. The relationship between fecundity and the subsequent change in genotype frequencies appeared poor, which implies that the relationship is strongly dependent upon life history parameters that were not measured. Fittnes values were estimated for the three most common esterase genotypes, of which the genotype MS seemed to have a long-term fitness superiority, and the genotype FM was equal or slightly superior to the major genotype MM. On the other hand, the variance of fitness values was high for the heterozygous genotypes, which indicates strong selection against them at times. It is suggested that the genotype MM is a generalist which can survive all seasons without great losses unlike the more specialized genotypes. The ephippial eggs hatching over a long period of time could have a stabilizing effect on the clonal structure of temporary Daphnia populations.