Isolation-by-Distance and Outbreeding Depression Are Sufficient to Drive Parapatric Speciation in the Absence of Environmental Influences
Figure 2
Scatterplots of Genetic Distance versus Spatial Distance.
Shown are scatterplots of genetic distance versus Euclidean spatial distance between grid cell centers for 100,000 pairs of randomly selected individuals. Genetic distance was measured by comparing a randomly selected haploid from each chromosome, as described in the text. Simulation parameters were as in Figure 1 for A, B, and C. Plots 2A and 2B showed a tendency toward increasing genetic distance with increasing spatial distance, evidenced by the upward-sloping black trend line, but only the combination of isolation-by-distance and outbreeding depression (A) clearly showed multiple clusters representing distinctive genetic subpopulations. For the simulation run with large dispersal distance (C), genetic information was mixed across the landscape grid too quickly for local pockets of genetically distinct types to emerge, and the entire grid was filled with genetically similar, closely related individuals. Simple, linear regression lines are shown in (A) and (B). The regression line is not shown in (C) because the slope is not well defined by the data.