Introgression of alleles and characters adaptive to specific environment from a species to another has a potential role in the colonization of the environment by the recipient species.
In coastal oak forests in northern Japan, there are two inter-fertile oak species, Quercus dentata (Qd) on the coastal side and Q. mongolica var. crispula (Qc) on the inland side. Qd is rare in high latitudes, where a coastal Qc ecotype is distributed on the coastal side. Multiple-trait phenotypes, genome-wide genotypes, and coastal stress were examined in inland Qc, coastal Qc, and coastal Qd populations to elucidate genetic variation in the traits and signature of introgression from coastal Qd to coastal Qc populations.
Phenotypes and genotypes varied among the populations, and coastal Qc was intermediate between inland Qc and coastal Qd. Phenotypes depended on genotypes without environmental effects of coastal stress. The ABBA-BABA test showed genome-wide introgression from coastal Qd to coastal Qc. Few genomic regions indicated the selection of introgressed alleles. Demographic history indicated relatively frequent gene flow between coastal Qc and both inland Qc and coastal Qd.
The findings showed genetic variation in traits that seem adaptive to coastal environment and environment-dependent introgression at genome-wide loci.