Common-garden study of introgression at loci associated with traits
adaptive to coastal environment from Quercus dentata into Q. mongolica
var. crispula
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 between Qc 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 Qa
backcrossed to Qc. Phenotypes of Qa trees were intermediate between
those of Qc and Qd trees. Size of Qa 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.