Approximate Bayesian computation
Tournament comparisons of invasion scenarios indicated that each of the four invasive populations in north America were more closely related to populations from Europe than to each other, or to an unsampled extra-European “ghost” population, suggesting four separate introduction events from Europe for winter moth (Figure 4). Comparison of the Nova Scotia population to the Western European, Central European, and Eastern European genetic clusters, indicated that it was most likely introduced from Central Europe (Supplemental Appendix S1 Figure S10a), and this relationship received high support based on logistic regression analysis (P = 0.98). The Oregon population most likely originated from Western Europe (Supplemental Appendix S1 Figure S10b), and this relationship received high support based on logistic regression analysis (P = 0.96). The British Columbia population most likely represents an additional independent introduction from Central Europe (Supplemental Appendix S1 Figure S10c), and this relationship received high support based on the logistic regression analysis (P = 1.00). The population in the northeastern United States population was also reconstructed as a third introduction from Central Europe (Figure 4), and this relationship was also highly supported (P = 1.00). Based on examinations of the posterior estimates, each of the invasive populations experienced a strong genetic bottleneck when they diverged from European populations ~100 ya (Supplemental Appendix S1 Table S3). Visualization of the PCAs for the supported scenario from each tournament based on the Perform Model Checking analysis in DiyABC, indicated that posterior values from simulated datasets formed a distinct cloud encompassing the sample dataset (Supplemental Appendix S1 Figures S11 through S14).