Supplementary Materials Table S1 Priors used for approximate bayesian computation (ABC) analyses. N1= Effective population size (Ne) of Nothofagus cunninghamii from Tasmania; N2 = Ne of Nothofagus cunninghamii from central highland Victoria; NA= Ne of the ancestral population; NF1 = Ne of the founding population for Tasmania, NF2 = Ne of the founding population for VictoriaT1 and T2 = times of divergence in generations of the respective populations; DB = the duration of the bottleneck associated with the foundation of new populations. Conditions were set so that DB<T1, NF1<N1, NF2<N2 and N2<N1 with prior probabilities of each scenario set to equal. The mean mutation rate was set to between 10-3 and 10-5 mutations per locus per generation. Parameter Minimum Maximum N1 10 10000 N2 10 10000 NA 10 10000 NF1 10 10000 NF2 10 10000 T1 10 10000 T2 10 10000 DB 10 10000 Mean mutation rate 1.00E-05 1.00E-03 Individual locus mutation rate 1.00E-05 1.00E-02 Mean coefficient P 1.00E-01 3.00E-01 Individual locus coefficient P 1.00E-02 9.00E-01 Mean SNI rate 1.00E-08 1.00E-05 Individual locus SNI rate 1.00E-09 1.00E-04 Effective Population size Time scale in generations Mutation model Table S2 Results of ABC analyses for estimated historical parameters of Nothofagus cunninghamii based scenario 3. N1= Effective population size (Ne) of Tasmania; N2 = Ne of central highland Victoria; t1 = time of divergence in generations; NA= Ne of the ancestral population; µmic_1= mean mutation rate; pmic = number of repeat motifs added or removed from the microsatellite in each mutation step and snimic = the single insertion nucleotide rate. Means, medians, modes and quantiles are given. Parameter N1 N2 t1 NA µmic_1 pmic_1 snimic_1 mean 9.31E+03 1.45E+03 2.96E+02 1.27E+03 8.32E-04 2.73E-01 8.22E-06 median 9.50E+03 1.23E+03 2.24E+02 7.21E+02 8.55E-04 2.87E-01 9.86E-06 mode 9.98E+03 9.34E+02 1.67E+02 2.32E+02 1.00E-03 3.00E-01 1.00E-05 q025 7.53E+03 4.03E+02 5.94E+01 5.64E+01 5.32E-04 1.70E-01 5.52E-07 q050 7.98E+03 4.94E+02 7.70E+01 1.00E+02 5.83E-04 1.94E-01 1.35E-06 q250 9.02E+03 8.46E+02 1.49E+02 3.53E+02 7.44E-04 2.62E-01 7.52E-06 q750 9.79E+03 1.73E+03 3.44E+02 1.51E+03 9.43E-04 3.00E-01 1.00E-05 q950 9.97E+03 3.17E+03 7.05E+02 4.48E+03 1.00E-03 3.00E-01 1.00E-05 q975 9.98E+03 4.03E+03 9.05E+02 6.18E+03 1.00E-03 3.00E-01 1.00E-05 Table S3 Mean relative bias of the ABC analyses for estimated historical parameters of Nothofagus cunninghamii based on the present data sets for scenario 3. Parameters are explained in the caption for Fig. S1. Parameter Means Medians Modes N1 0.064 0.0689 0.1366 N2 0.088 0.0358 -0.056 t1 0.206 0.119 0.0144 NA 1.273 1.089 0.5872 µmic_1 0.236 0.138 0.0061 pmic_1 0.04 0.0256 -0.0345 snimic_1 14.035 4.2132 -0.7812 Table S3 Posterior probabilities of all 12 scenarios estimated with a maximum of 1% of the simulated datasets. n = the number of simulated datasets closest to the observed used to estimate the posterior. Scenario n 6858 13716 20574 27432 34290 41148 48006 54864 61722 68580 1 0.0042 (0.0000-0.0954) 0.007 (0.0000-0.0667) 0.0098 (0.0000-0.0558) 0.0108 (0.0000-0.0491) 0.0118 (0.0000-0.0454) 0.0123 (0.0000-0.0421) 0.0126 (0.0000-0.0396) 0.013 (0.0000-0.0378) 0.0134 (0.0000-0.0365) 0.0138 (0.0000-0.0356) 2 0.409 (0.2836-0.5345) 0.3932 (0.3034-0.4829) 0.3801 (0.3065-0.4537) 0.3702 (0.3062-0.4342) 0.3648 (0.3072-0.4224) 0.3579 (0.3053-0.4106) 0.3526 (0.3037-0.4014) 0.3483 (0.3026-0.3941) 0.3454 (0.3021-0.3887) 0.343 (0.3019-0.3842) 3 0.3257 (0.2012-0.4501) 0.3645 (0.2831-0.4459) 0.3765 (0.3126-0.4404) 0.383 (0.3271-0.4389) 0.3879 (0.3371-0.4387) 0.3934 (0.3464-0.4404) 0.3969 (0.3530-0.4409) 0.3987 (0.3573-0.4402) 0.3993 (0.3600-0.4387) 0.3993 (0.3618-0.4368) 4 0.0048 (0.0000-0.0960) 0.0064 (0.0000-0.0664) 0.0064 (0.0000-0.0530) 0.0068 (0.0000-0.0458) 0.0069 (0.0000-0.0411) 0.0071 (0.0000-0.0375) 0.0073 (0.0000-0.0348) 0.0076 (0.0000-0.0330) 0.0081 (0.0000-0.0318) 0.0086 (0.0000-0.0309) 5 0.0092 (0.0000-0.0996) 0.0104 (0.0000-0.0699) 0.0121 (0.0000-0.0583) 0.0136 (0.0000-0.0521) 0.0146 (0.0000-0.0484) 0.0151 (0.0000-0.0452) 0.0153 (0.0000-0.0426) 0.0156 (0.0000-0.0407) 0.016 (0.0000-0.0394) 0.0162 (0.0000-0.0383) 6 0.0003 (0.0000-0.0925) 0.0003 (0.0000-0.0613) 0.0004 (0.0000-0.0478) 0.0004 (0.0000-0.0400) 0.0004 (0.0000-0.0353) 0.0005 (0.0000-0.0315) 0.0005 (0.0000-0.0286) 0.0005 (0.0000-0.0265) 0.0006 (0.0000-0.0248) 0.0006 (0.0000-0.0235) 7 0.0786 (0.0000-0.1612) 0.0594 (0.0045-0.1143) 0.0586 (0.0158-0.1014) 0.0587 (0.0229-0.0944) 0.0579 (0.0264-0.0893) 0.0579 (0.0299-0.0859) 0.0583 (0.0328-0.0837) 0.059 (0.0356-0.0825) 0.06 (0.0380-0.0819) 0.0609 (0.0402-0.0817) 8 0.0368 (0.0000-0.1247) 0.0342 (0.0000-0.0926) 0.0342 (0.0000-0.0796) 0.0339 (0.0000-0.0719) 0.0332 (0.0000-0.0666) 0.0326 (0.0029-0.0623) 0.0325 (0.0055-0.0594) 0.0325 (0.0077-0.0574) 0.0319 (0.0087-0.0551) 0.0316 (0.0097-0.0535) 9 0.0395 (0.0000-0.1253) 0.0303 (0.0000-0.0874) 0.0282 (0.0000-0.0726) 0.0275 (0.0000-0.0646) 0.0269 (0.0000-0.0595) 0.0273 (0.0000-0.0562) 0.0277 (0.0015-0.0539) 0.0284 (0.0042-0.0525) 0.0289 (0.0064-0.0514) 0.0293 (0.0081-0.0505) 10 0.0292 (0.0000-0.1166) 0.0269 (0.0000-0.0848) 0.0264 (0.0000-0.0714) 0.0276 (0.0000-0.0651) 0.0273 (0.0000-0.0603) 0.0273 (0.0000-0.0566) 0.0276 (0.0011-0.0541) 0.0277 (0.0033-0.0521) 0.0277 (0.0049-0.0505) 0.0277 (0.0062-0.0492) 11 0.0166 (0.0000-0.1056) 0.0168 (0.0000-0.0756) 0.015 (0.0000-0.0607) 0.014 (0.0000-0.0522) 0.0139 (0.0000-0.0475) 0.0135 (0.0000-0.0434) 0.0132 (0.0000-0.0403) 0.0129 (0.0000-0.0379) 0.0128 (0.0000-0.0362) 0.0128 (0.0000-0.0348) 12 0.046 (0.0000-0.1312) 0.0506 (0.0000-0.1069) 0.0523 (0.0085-0.0962) 0.0535 (0.0167-0.0902) 0.0544 (0.0220-0.0867) 0.0552 (0.0263-0.0840) 0.0555 (0.0293-0.0817) 0.0557 (0.0315-0.0799) 0.056 (0.0333-0.0786) 0.0562 (0.0349-0.0775) Figure S1 Proportion of membership of clusters identified using Structure assuming 2 clusters. Note the high incidence of the typically Tasmanian cluster (red) in the two southernmost Victorian populations. Barriers (predicted with BARRIER version 2.2) to gene flow are indicated by grey lines; the thickness of the edge of a barrier is proportional to the extent of the barrier and the adjacent numbers relate to the number of times the barrier was observed across samples. Figure S2. The 12 scenarios tested for ABC analysis. The colours represent populations that are either observed (red for Victoria and dark blue for Tasmania) or inferred past populations (other colours). A change in colour represents formation of a new population. Figure S3 The partitioning of genetic variance in N. cunninghamii based on (a) 10 loci, and (b) 12 loci. The 10 locus analysis should provide a less biased estimate of the partitioning of variance because it excludes the two loci with high levels of null alleles, which can cause overestimation of among individual variance. The levels are: between states, among populations within states, among subpopulations within populations, among individuals within subpopulations and within individuals, as identified by AMOVA. a) Tasmania 0.30 0.25 Fst(1-Fst) 0.20 0.15 0.10 0.05 0.00 0.0 0.5 1.0 -0.05 1.5 2.0 2.5 3.0 2.0 2.5 3.0 Log(1+GGD) b) Victoria 0.30 0.25 Fst(1-Fst) 0.20 0.15 0.10 0.05 0.00 0.0 0.5 -0.05 1.0 1.5 Log(1+GGD) Figure S4 Plots of genetic distance versus geographic distance for (a) Tasmanian subpopulations, and (b) Victorian subpopulations. Mantel tests showed very highly significant associations between geographic and genetic distances within Victoria both including and excluding the isolated Kinglake population (P = 0.006 and P<0.001, respectively), but no significant association within Tasmania (P = 0.125). (a) Tasmanian Sub Populations 6 Allelic richenss 5 4 3 R² = 0.0183 (not significant; P > 0.05) 2 1 0 0 200 400 600 800 1000 1200 1400 Altitude (m above sea level) Allelic richness (b) Victorian Sub Populations 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 R² = 0.0006 (not significant; P > 0.05) 0 200 400 600 800 1000 1200 1400 1600 Altitude (m above sea level) Figure S5. Relationships between allelic richness (Ar) and altitude of all subpopulations in (a) Tasmania and (b) Victoria. Figure S6 Allele frequency histograms showing the count of alleles across all 12 loci within six allele frequency classes within each of the 18 Nothofagus cunninghamii populations from Tasmania (a-k) and Victoria (l-r). Figure S7 The posterior distribution (green lines) and prior distribution (red lines) of the effective populations size of (a) Tasmanian populations, (b) Victorian populations and (c) the time in generations of the divergence of these populations. The numbers in brackets are the median values of the posterior. a) b) c)