Estimates related to the age of the hybrid zone.

The first two columns report the observed differences in Procrustes units and standard deviates and the last column reports the number of years since secondary contact if there is no barrier to gene flow. The amount of differentiation expected by drift over 10,000 years (see text) is 8.5 standard deviates if small effective population size is assumed (Ne = 70) and 0.3 standard deviates if a large population is assumed (Ne = 70,000).