Aim According to palaeo‐biome reconstructions, the subtropical evergreen broadleaved forests (EBLF) in East Asia contracted to a narrow belt south of 24° N during the Last Glacial Maximum (LGM). Yet numerous phylogeographical studies of EBLF plants have inferred glacial refugia north of this area. Here, we aim to further elucidate the Quaternary dynamics of EBLFs using the widespread shrub Lindera aggregata as model. Location Subtropical China. Taxon Lindera aggregata (Sims) Kosterm (angiosperms). Methods Four chloroplast DNA (cpDNA) fragments and 15 low‐copy nuclear genes (LCGs) were sequenced in 19 populations. The time to the most recent common ancestor (TMRCA) was estimated using secondary calibrations. Bayesian algorithms were used to infer population clustering, phylogeny and divergence time. Historical gene flow was estimated using a maximum‐likelihood algorithm. Potential habitats at present and during the LGM were predicted using ecological niche modelling. Results The TMRCA estimate was 1.78 Myr. We observed a shallow cpDNA network organized around one dominant haplotype. The LCGs revealed three distinct genetic clusters that reflected contrasting historical population dynamics. The most ancient cluster was located south of the Nanling and Wuyi Mountains and indicated long‐term population persistence in multiple refugia. The area further north was occupied by two disjunct clusters that dated back to the LGM and showed signatures of a rapid northward expansion from two refugia. We detected noteworthy pollen‐mediated secondary admixture between all three clusters including somewhat preferential southward gene flow. Main conclusions Lindera aggregata represents a rare example of extensive post‐glacial range expansion across the EBLF biome (expansion‐contraction model) that contrasts with its generalized long‐term population stability in the southernmost range parts. Our findings also provide rare evidence for noteworthy post‐glacial gene flow into long‐term refugial populations. They correspond relatively well with palaeo‐biome reconstructions and support the hypothesis that the EBLF has undergone extensive post‐glacial community reshuffling.
The evolution of subtropical evergreen broadleaved forests (EBLFs) in East Asia is interesting while complicated. Genus‐level phylogenies indicate that the origins of EBLFs could trace back to the Oligocene–Miocene boundary or even the Eocene, while population‐level phylogeographic evidence suggests that they diversified after the Miocene, particularly in the Pleistocene. Here, we review the origins of dominant plant species to better understand the evolution of EBLFs. We compiled published estimates of the timing of origin of dominant species and diversification of evergreen relict genera from East Asian EBLFs. We also traced and visualized the evolution of EBLFs in the region using dated phylogenies and geographic distributions of the reviewed taxa. Most (76.1%) of the dominant species originated after the late Miocene, ca. 8 million years ago. Of the 10 evergreen relict genera, eight diverged near the late Miocene–Pliocene boundary or during the late Pliocene, and the remaining two diverged during the Pleistocene. Over the past 8 million years, geo‐climatic changes have triggered origins of most of the dominant EBLF species and provided refugia for evergreen relict genera. Three pulsed phases of evolution are suggested by genetic studies at the genus, species, and population levels. Fossil evidence and spatiotemporal investigations should be integrated to fully understand the evolution of EBLFs in East Asia.
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