Postglacial population expansion of Dacrydium pectinatum (Podocarpaceae) in Hainan, southern China, based on cpDNA trnL-F nocoding sequence data

Abstract

This study determined the sequences of chloroplast DNA (cpDNA) trnL-F non-coding regions of individuals of a tropical coniferous species, Dacrydium pectinatum, collected from 12 natural populations located in Hainan Province, southern China. Sequence length varied from 868 bp to 876 bp, indicating length polymorphism. Base composition in the sequences was high in A+T content between 64.17% and 64.95%, and no recombination event occurred (Rm = 0). Thirty haplotypes were identified based on statistical parsimony algorithm by running the TCS program. Populations of D. pectinatum in Hainan were lacking genetic differentiation. Such a deduction was supported by the observed F_ST values (0.00), AMOVA (24.17% of molecular variance attributed to difference among populations, P>0.05), high values of Nm (ranging from 1.92 to 2.50) and the branching structure in neighbor-joining (NJ) tree constructed from haplotypes. A star-like  pattern was exhibited in the TCS network of trnL-F haplotypes, and majority of the haplotypes coalesced near the tips in NJ tree. Gene genealogies of cpDNA haplotypes proposed a recent population expansion of D. pectinatum in Hainan, which was further supported by the results from Tajima s D test and mismatch distribution analysis. Our data, in conjunction with geological and palynological evidences, showed that in the Holocene, due to global warming, refugee populations of D. pectinatum in Hainan might experience a range expansion.