Seasonal changes of the enzyme gene pool in water‐striders (Gerris)

摘要

Enzyme gene variation was studied in two successive generations of one Gerris argentatusone G. odontogasterand six G. lacustrispopulations in two years. At several polymorphic loci, the allele frequencies in the overwintered populations differed significantly from those in their offspring. In both years the genetic distances between the overwintered G. lacustrispopulations were greater than the distances between the offspring populations. The average genetic distance between the generations was of the same order as or greater than between the populations within the same generation. At one locus, Est-3of G. lacustristhe allele frequency changes were similar in all populations in one year, and there was a heterozygote excess in all offspring populations. This indicates that selection operating on this or some associated locus is effective. Seasonal selection pressures were also indicated by the increased homogeneity of the populations during summer. Significant changes observed at other loci may be explained by random processes, but they may also be due to natural selection.