Chloroplast DNA phylogeographic analysis reveals significant spatial genetic structure of the relictual tree Davidia involucrata (Davidiaceae)

The dove tree, Davidia involucrata Baill. (Davidiaceae), is a relict species endemic to China. Human activities and the strict requirements for seedling recruitments have led to the decline in number of individuals in extant natural populations of this species. In order to provide information for the design of conservation management strategies for D. involucrata, we investigated the phylogeographical pattern of this relict tree. Our sampling included 256 individuals from 32 natural populations of D. involucrata in China and we sequenced six chloroplast DNA (cpDNA) non-coding regions. We distinguished a total of 13 different cpDNA haplotypes. From the cpDNA variation in D. involucrata, we found a very high level of regional differentiation (F (ST) = 0.812) and a strong phylogeographical pattern (N (ST) = 0.996 > G (ST) = 0.981, P < 0.05). Phylogenetic analysis reveals three main cpDNA haplotype lineages and four population groups. The split between these geographical groups can be dated back from the late Pliocene to early Pleistocene. Non-overlapping distribution of chloroplast haplotypes and high genetic differentiation among four distinct geographical groups suggest that D. involucrata probably survives in four separate glacial refugia. Our findings have an important implication for conservation of its genetic diversity. The deduced glacial survival areas for D. involucrata should be recognized as four "evolutionary significant units" and be considered as separate targets in conserving its genetic diversity.