Comparative Phylogeography Of Three Dominant Tree Species In Evergreen Broad-leaved Forest (EBLF) Of Subtropical China

The subtropical China is characteristic of evergreen broad-leaved forest(EBLF) and rich flora with many relict plants. Targeting on three typical evergreen plant species,Castanopsis tibetana, Machilus thunbergii, and Schima superba, this study aims to characterize the distribution histories of the three species during the Quaternary climate changes, using comparative phylogeographical methods, combined with species distribution modelling(SDM).Population samples of C. tibetana(45 populations/332 individuals), M. thunbergii(46/390), and S. superba(54/515), were collected across their distribution ranges. Two chloroplast intergenic spacers, psbA-trnH and rpl32-trnL(UAG), were sequenced to assess genetic diversity, genetic structure, and historical demography. The overall haplotype diversity values are all considerably high in C. tibetana, M. thunbergii, and S. superba(hT= 0.797, 0.765, and 0.644, respectively). This study revealed diverse phylogeographic patterns in three dominant trees, i.e., multiple refugia(In Situ Survival model,ISS model)without significant phylogeographic structure in C. tibetana, glacial retreat and post-glacial(Contraction and Expansion, CE model) recolonization in M. thunbergii, and multiple refugia(ISS model) with significant phylogeographic structure in S. superba. This study suggests that the constituents of EBLF could have responded idiosyncratically to climate changes during the Late Quaternary. Different phylogeographic patterns among co-distributed species suggesting that community assemblages of EBLF could have been changing over time, which may be the main reason responsible for the divergent results offered by phylogeographic analyses and palaeo-biome reconstructions(PBR).