Genetic structure of midwestern Ascaris suum populations: a comparison of isoenzyme and RAPD markers.

Isoenzyme and random amplified polymorphic DNA (RAPD) markers were used to characterize the genetics of geographic variation among population samples of Ascaris suum from midwestern localities. Independent estimates of fixation indices (FST) based on isoenzyme and RAPD markers showed the same general patterns of differentiation and substantial statistical correlation (r = 0.70). Of the total estimated gene diversity, 9.4% (isoenzyme) and 9.2% (RAPD) was distributed among infrapopulations. Geographic localities accounted for 7.8% (isoenzyme) and 6.2% (RAPD) of the total gene diversity. Only infrapopulations from a single farm were characterized by low fixation indices (isoenzyme and RAPD FST < 0.05). Isoenzyme and RAPD markers revealed moderate genetic differentiation among infrapopulations and localities, which indicates significant population subdivision among A. suum from farms within geographic regions. Departures from random mating were revealed by deficiencies of heterozygotes within infrapopulations and by high positive values of FIS among and between infrapopulations. The average inbreeding (FIS) coefficient among all infrapopulations was 0.22. Thus, the genetic composition of these A. suum infrapopulations, whether from a general geographic region of a single farm, was not consistent with a model of random recruitment from a larger panmictic pool of parasite life cycle stages.