Phylogeography of Davidia involucrata (Davidiaceae) Inferred from cpDNA Haplotypes and nSSR Data

Davidia involucrata Baill. (Davidiaceae), commonly known as "Chinese dove tree", is a rare and endangered species endemic to China. Little is known about the genetic structure and population history of D. involucrata. Both cpDNA and nSSR markers showed high genetic diversity among D. involucrata populations (H-S = 0.717; h(T) = 0.893; p(T) = 3.14 x 10(-3)). The genetic divergence of all D. involucrata populations was significantly higher in the cpDNA (F-ST = 0.765) than in the nuclear DNA (F-ST = 0.239), possibly reflecting a more important role of pollen dispersal than the seed in the formation of the genetic structure of Davidia. Phylogeographic analyses suggested that the populations of D. involucrata were divided into the eastern and western lineages with the Sichuan Basin as the boundary, separating the Sino-Himalayan and Sino-Japanese Forest subkingdoms. Divergence of the two lineages was estimated to have occurred around 4.81 Mya during the Late Miocene/Early Pliocene. Mismatch distribution and neutrality tests didn't show significant population growth and range expansion in either lineage, suggesting the in situ survival of multiple populations during the Quaternary glaciation without range expansion. There are two potential refugia of Davidia involucrata in Southwest and Central China and natural reserves need to be established to preserve the genetic diversity of the species in the refugia.