Figure 2

Evolutionary scenarios to illustrate model checking. The three presented scenarios are often compared when making ABC inferences on the routes of introduction of invasive species. S is the source population in the native area, and U, the unsampled population in the introduced area that is the source of populations 1 and 2 in scenario 3. The stars indicate the bottleneck events occurring in the first few generations following introductions. We here considered that the dates of first observation were well known so that divergence times could be fixed at 5, 10, 15 and 20 generations for t1, t2, t3 and t4, respectively. The data sets consisted of simulated genotypes at 20 (independent) microsatellite loci obtained from a sample of diploid individuals collected from the invasive and source populations (30 individuals per population). The pseudo-observed test data set that we analyzed to illustrate model checking was simulated under scenario 3 with an effective population size (NS) of 10,000 diploid individuals in all populations except during the bottleneck events corresponding to an effective population size (NFi) of 10 diploid individuals for 5 generations. Prior distributions for ABC analyses (discrimination of scenarios and estimation of posterior distribution of parameters) were as followed: Uniform[1000; 20000] for and logUniform[2; 100] for the demographic parameters NS and NFi, respectively, and same distributions as those given in the text of Methods (section "Mixing microsatellite, mtDNA, and/or nuclear DNA sequence data") for microsatellite markers.