Postglacial Lineage Admixture in the Contact Zones of the Two Japanese Deciduous Broad-leaved Tree Species Estimated by Nuclear Microsatellite and Chloroplast DNA Markers
When historically isolated populations meet during postglacial expansion, a mixed distribution of distinct DNA lineages called contact zones is created. The gradual dissolution of the spatial genetic structures in contact zones should be related to differences in pollen and seed dispersal, given no restriction on gene flow by e.g. reproductive isolation. We aimed to clarify effects of pollen dispersal modes on nuclear DNA (nrDNA) genetic structures of two codistributed species with different pollen dispersal modes, by analyzing nuclear microsatellites of the insect-pollinated Magnolia obovata and the wind-pollinated Carpinus laxiflora, which show highly consistent contact zone locations in terms of chloroplast DNA (cpDNA). The genetic structure based on the nrDNA and that based on the cpDNA were concordant in M. obovata, but not so concordant in C. laxiflora . Pollen dispersal ability is higher in the wind-pollinated C. laxiflora than in M. obovata, resulting in the higher estimated pollen/seed migration ratio in C. laxiflora than in M. obovata. Therefore, the extent of postglacial lineage admixture in nrDNA was predominant in C. laxiflora . Our results suggested that differences in pollen dispersal ability may affect the nrDNA genetic structure between co-distributed species with common migration histories in the same area.