Abstract
Adaptive introgression has been proposed in oaks (genus Quercus ).
In northern Japan, Q. mongolica var. crispula (Qc )
is common in inland habitats, and Q. dentata (Qd ) occurs
in coastal habitats. At the northern distributional limit of Qd ,Q. × angustilepidota (Qa ), a hybrid taxon betweenQc and Qd , occurs in coastal habitats. The three taxa,Qc , Qa , and Qd , were transplanted to inland and
coastal common gardens (sites). Genotypes at 27495 loci, phenotypes of
eight traits of leaves and shoots, and 30-year-old tree size were
measured for 224 individuals in both sites. Genotypic variation revealed
a hybrid zone between Qc and Qd , including both
northern-edge Qd admixed with Qc and coastal Qabackcrossed to Qc . Phenotypes of Qa trees were
intermediate between those of Qc and Qd trees. Size ofQa and Qd trees was smaller than that of Qc trees
in the inland site but was larger in the coastal site, suggesting
adaptation of Qa and Qd to coastal environment. Local
ancestry was estimated from phased genotypes of admixed trees using
reference genotypes of 47 Qc and 25 Qd trees, indicating
heterogeneous ancestry along chromosomes. Association mapping of
genotypes and admixture mapping of ancestry suggested that some loci
potentially associated with four traits were related to stress response
and were located at introgressed genomic regions. Further studies are
necessary to show the genetic basis of adaptive introgression resulting
in Qd -like phenotypes of Qa in coastal habitats.