Nested clade analysis of Dunnia sinensis (Rubiaceae), a monotypic genus from China based on organelle DNA sequences

Dunnia sinensis, a monotypic genus of theRubiaceae endemic to the southeast mainlandChina, is an endangered species due to habitatdestruction over the past decades. Informationon levels and apportionment of geneticvariation across populations and geographicalregions is fundamental to conservation. In thepresent study, we used organelle DNA variationand nested phylogeographic analyses to test theisolation-by-distance model in this specieswith wind-mediated seed-dispersal and todistinguish ongoing gene flow from historicalprocesses. As expected, low levels of geneticvariation were detected at the ribosomal ITSregion of mtDNA (θ = 0.0019± 0.0002) and the atpB-rbcLintergenic spacer of cpDNA (θ =0.0022 ± 0.0009) in the rare species. Sixand seven haplotypes of mt- and cpDNA wereidentified from 125 individuals, respectively,according to the reconstructed neighbor-joiningtrees. Both data sets suggested consistentphylogenies that recovered two differentiatedlineages corresponding to western (Yangchun)and eastern (four others populations) portionsof the range. Hierarchical analyses of themolecular variance (AMOVA) of mt- and cpDNAindicated that molecular variance wasattributable to the difference between regions(Φct = 0.911 and 0.771 for mt- and cpDNA,respectively) in D. sinensis. Based ongeographic distributions of haplotypes in thehaplotype networks, significant geneticdifferentiation between the two geographicregions, which can be seen as evolutionarilyconservation units, was associated withhistorical fragmentation. In contrast, limitedgene flow with occasional long-range dispersalshaped the apportionment of organelle DNAalleles among populations of the easternregion, within which two incompletely isolatedphylogeographic groups can be recognized asconservation units for management.