Si-Si Zheng

The interplay between historical biogeography and environmental selection shapes the genetic architecture of species; however, their relative contributions in widespread and ecologically important tree species remain poorly understood. In the Sino-Japanese Floristic Region, the East China Sea has alternately acted as a barrier and a corridor during glacial-interglacial cycles, influencing species isolation and contact. However, the extent to which these historical dynamics, along with environmental gradients, have driven adaptive evolution in dominant forest trees remains unresolved. In the present study, we integrated phylogeographic reconstruction and landscape genomics based on whole-genome resequencing data from 171 individuals across 35 populations to investigate the evolutionary history and adaptive mechanisms of Quercus gilva, a keystone evergreen oak, in East Asian subtropical forests. Population genomic analyses revealed two deeply divergent genetic groups: the China group and the Japan–Korea group, and demographic modeling indicated that their divergence dates back to the Miocene epoch. The relatively high genomic diversity of Q. gilva may result from the absence of severe genetic bottlenecks throughout its evolutionary history, multiple microrefugia during the glacial periods, and postglacial secondary contact. Notably, Quaternary glacial cycles repeatedly facilitated gene flow and admixture between these groups via exposed land bridges. Landscape genomic analyses further demonstrated that adaptive divergence in Q. gilva is shaped by both geographic isolation and environmental gradients, with annual precipitation emerging as the primary climatic driver. This study provides a genome-wide perspective on how historical biogeography and environmental selection interact to shape the genetic architecture of a dominant subtropical evergreen forest species, offering novel insights into the evolutionary dynamics and adaptive evolution across East Asian biodiversity hotspots.

Environmental factors such as mountain tectonic movements and monsoons can enhance genetic differentiation by hindering inter- and intra-specific gene flow. However, the phylogeographic breaks detected within species may differ depending on the different molecular markers used, and biological traits may be a major confounding factor. Pterocarya hupehensis is a vulnerable relict species distributed throughout the Sichuan Basin. Here, we investigated the phylogeographic patterns and evolutionary history of P. hupehensis using chloroplast DNA and restriction site-associated DNA sequencing data from 18 populations around the Sichuan Basin. The 24 chloroplast haplotypes separated into western and eastern lineages at approximately 16.7 Mya, largely coincident with a strengthening of the East Asian monsoon system during the early to middle Miocene. Both cpDNA and nuclear DNA datasets consistently identified distinct western and eastern lineages whose phylogeographic break conformed to the boundary of the Sino-Himalayan and Sino-Japanese forest sub-kingdoms. However, in contrast to the nuclear gene data, the cpDNA data revealed further divergence of the eastern lineage into northern and southern groups along the Yangtze River, a result that likely reflects differences in the extent of pollen vs seed dispersal. During the temperature decline in the penultimate (Riss) glacial period of the Pleistocene epoch, P. hupehensis experienced a genetic bottleneck event, and ecological niche modeling suggests that a subsequent population expansion occurred during the last interglacial period. Our findings not only establish a basis for conservation of this species, but also serve as a case study for the effects of geography and climate change on the evolutionary history of wind-pollinated relict plants.