Differential admixture and introgression in <i>Cerasus</i> hybrid zones at the south rear edge of cool‐temperate <i>C. sargentii</i> and the north leading edge of temperate <i>C. leveilleana</i>

Abstract Genetic and phenotypic clines in hybrid zones can differ due to various extents of hybridization and selection in heterogeneous environments. Temperate Cerasus leveilleana ( Cl ) and cool‐temperate C. sargentii ( Cs ) form hybrid zones along elevational gradients. Because their geographic distributional ranges are largely overlapped, the hybrid zones are located across a wide latitudinal range in Japan. We compared variation in genotypes and phenotypes in hybrid zones among the south edge of Cs (south site), the north edge of Cl (north site), and the core of their ranges (central site). Genetic differentiation in nuclear microsatellite genotypes between Cl and Cs was lower, and the proportion of admixed individuals was higher in the south site than in the central and north sites. The difference in the leaf hair number between Cl and Cs was smaller in the south site than in the central and north sites. Flowering periods at the same elevation were about 7 days earlier in Cs than in Cl in the central site, while the periods were about 9 days earlier in the south and north sites. These results suggest more admixture in the south site, which may result in introgression in a leaf trait, although staggered flowering is maintained. These findings imply that genetic admixture and phenotypic introgression have been facilitated, except for the latter in traits contributing to reproductive isolation, in the hybrid zone at the south rear edge of either species under the warming trend after the last glacial period.