3.1 | Genotypes
In the inland site, 575 living and 197 dead trees were found, and 106 trees were sampled from the living trees (Figure S2, Data S1 in Supporting Information). In the coastal site, 350 living and 46 dead trees were found, and 118 trees were sampled from the living trees (Figure S3, Data S1). Taxonomic assemblages of sampled trees were biased to Qc (41 Qc , 40 Qa , and 25 Qd trees) in the inland site and biased to Qd (12 Qc , 48 Qa , and 58Qd trees) in the coastal site probably due to different mortality in inland and coastal habitats (Table S1).
SNP genotypes at 27495 ddRAD loci were obtained from the 224 sampled trees in both sites. Bayesian clustering for SNP genotypes demonstrated a larger increase in log-likelihood from one to two clusters (K = 1–2) and an additional smaller increase from two to three clusters (K = 2–3; Figure S5). When two clusters representing Qcand Qd were recognized, genetic differentiation based onF ST between these clusters was 0.183. Ancestry proportion of the Qd cluster (Q ) was lower in Qctrees (0.00 < Q < 0.17), intermediate inQa trees (0.00 < Q < 0.45), and intermediate or higher in Qd trees (0.23 < Q< 1.00; Figure S5). These findings suggested that genetic variation mainly existed between Qc and Qd and that their admixture characterized Qa and a part of Qd .
For the sampled trees in both sites, the Qd ancestry (S ) and inter-ancestry heterozygosity (H ) were estimated from allele frequencies of the Qc and Qd clusters obtained from the Bayesian clustering. Genomic compositions shown in the coordinates ofS and H indicated nearly random admixture between the ancestral populations of Qc and Qd (Figure 2). In both sites, Qd trees from provenances near the distributional limit in the northernmost area of Hokkaido showed lower Qd ancestry (0.23 < S < 0.91) than those from provenances in the other southern areas (0.78 < S < 1.00), and Qa trees from coastal provenances north to the distributional limit of Qd showed higher Qd ancestry (0.00 <S < 0.45) than Qc trees from inland provenances in Hokkaido (0.00 < S < 0.06; Figure 2). These findings suggested a hybrid zone between Qc and Qdaround the northern distributional limit of Qd , including both northern-edge Qd populations admixed with Qc and coastalQa populations backcrossed to Qc .