Genetic structure and trait variation within a maple hybrid zone in North China provide evolutionary and ecological insights for ancient lineage evolution

Abstract Secondary contact zones can provide valuable evolutionary and ecological insights for elucidating patterns of divergent lineage evolution. The tertiary relict flora in East Asia can be divided into northern (“NEA”) and southern (“SEA”) regions. To date however, secondary contact zones of lineages from the NEA and SEA regions have rarely been studied. To test whether introgression occur between the ancient lineages and their evolutionary and ecological consequences, we conducted detailed genetic and ecological work within a maple hybrid zone in North China. Genetic structures of both adults and seeds populations were characterized. Spatial genetic pattern was checked along an altitude gradient. Flowering phenology was analyzed to test the existence of assortative mating. Leaf and fruit morphologies were compared between lineages. Our study confirm introgression occur between NEA and SEA lineages. Post-pollinator barriers predominantly contribute to a reduction in interlineage gene flow. Ecological niche differs between lineages along an altitudinal gradient. We clarify a long-standing classification debate with respect to Acer pictum subsp. mono and A. truncatum, though there are extensive morphological variation and overlaps between the species pair. Our study represents the first few detailed evolution and ecological investigation focusing on ancient NEA-SEA lineages hybrid zone.