Differences among genotypic frequencies of undisturbed and manipulated populations of Daphnia.

A lake population of Daphnia, and several subpopulations in large plastic enclosures within the lake and manipulated with respect to population densities and nutrient enrichment (acetate, nitrate, phosphate), exhibited differences among genotypic frequencies at the phosphoglucoisomerase locus. The lake and control populations exhibited similar genotypic frequencies which were significantly different from those found in the three manipulated populations. The similarity of the genetic reaction in the manipulated populations may be related to similarity of manipulation. All populations exhibited deviations from Hardy-Weinberg proportions in the form of heterozygote excess.