Genic differentiation of northern Finnish water‐strider (Gerris) populations

Abstract

Enzyme gene variability was studied in three Gerris (Heteroptera) species including 15 populations of G. laterialis Schumm., seven populations of G. odontogaster (Zett.) and five populations of G. lacustris (L.) in northern Finland. The study was undertaken to compare genic variation and differentiation in the species, which differ with respect to certain important characters (dispersion efficiency and isolation of populations, abundancy, commonness, geographical distribution) that could affect genic variation. Another purpose of the study was to compare the pattern of variation in northern Finnish G. lacustris and G. odontogaster populations to that revealed earlier in their southern populations. Average heterozygosity was lowest in G. lateralis and highest in G. lacustris. Northern G. lacustris and G. odontogaster populations were clearly less variable than their southern populations. G. odontogaster, the most efficient disperser, showed least differentiation among populations. The results confirm qualitatively the predictions based on population sizes, as the effective population size of G. lateralis should be reduced compared with the other species owing to its rareness and much higher proportion of individuals without flight‐ability. The results suggest that differences in the action of genetic drift processes in the three species can serve as competent explanations for differences in the amount of variability and differentiation. © 1980 Mendelian Society of Lund