Isolation-by-Distance and Outbreeding Depression Are Sufficient to Drive Parapatric Speciation in the Absence of Environmental Influences
Figure 3
Example of a Mismatch Distribution.
Shown are the frequencies of genetic distance classes between 500,000 randomly sampled pairs of haploid genomes. The multimodal distribution evident in this example indicated the existence of more than one distinctive gene pool in the population. The data here were drawn from generation 120,000 in a run where individuals contained n = 2 diploid chromosomes of l = 200 base pairs each, grid size was 400×400, population size was 128,000, maximum occupancy was 1 individual per cell, movement distance δ = 1.5, and mutation rate μ = 0.00005 per site per replication. Offspring viability dropped to 0 beyond a genetic distance of θ = 0.6. The presence of a distinct peak to the right of this threshold indicated the presence of reproductively incompatible populations. The peak to the far right never moved much beyond a genetic difference of 75%, the maximum value expected under the Jukes-Cantor mutation model [33]. The peak to the far left was also unmoving and remained centered near a genetic difference of θ0 = 0.05. This peak included all within-subpopulation comparisons. Peaks between these extremes always moved to the right; some eventually merged with the peak on the right, but most vanished first, indicating extinction of one or both subpopulations compared within the peak.