Population genetics of Polyphemus pediculus (Cladocera: Polyphemidae).

Population genetic studies of cyclically parthenogenetic organisms have focussed on members of the freshwater cladoceran crustaceans, and mainly on those populations which inhabit intermittent or permanent ponds. Little is known of the genetic structure of large-lake populations. The genetic structure of populations of the predatory freshwater littoral-zone cladoceran, Polyphemus pediculus from 20 palearctic lakes in Northern Germany was examined by electrophoresis to determine its breeding system and level of genetic polymorphism, and to compare its genetic structure with those of other Cladocera. Polyphemus was polymorphic for three of eight enzyme loci and most (20/23) genotypic frequencies were in Hardy-Weinberg equilibrium. These populations are thus panmictic, and most likely reproduce by cyclical parthenogenesis. There were heterozygote deficiencies at each of the polymorphic loci in the three deviant populations. Genetic differentiation between populations was evident at each locus, with significant spatial autocorrelation found at the Pgm locus. Population heterozygosity averaged 9.2 per cent with a mean of 1.5 alleles/locus. Mean number of composite genotypes per population was 6.0+/-1.0 (S.E.) with a range of 1-17 clones per population. P. pediculus thus has a population genetic structure similar to that of large-lake Daphnia populations.