Figure 3.—
Interspecific heterozygosity (vertical axis) vs. hybrid index (horizontal axis) in three interspecific hybrid zones of P. alba and P. tremula: Danube (Austria), Ticino (Italy), and Tisza (Hungary). Solid circles indicate observed values for individual genotypes sampled in each population; shaded circles indicate values for simulated F1's (center of each graph) and parentals (left and right end of each graph). Univariate 95% confidence intervals for simulated F1's (ellipses) allow detection of observed hybrid genotypes with reduced interspecific heterozygosity (individuals below the ellipses), indicative of recombinant hybrid generations. The graphs are based on 68 codominant microsatellites in the case of the Danube hybrid zone (Austria) and 18 codominant loci for the Ticino (Italy) and Tisza (Hungary) hybrid zones, respectively.