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 .