Phylogeographic analysis of the fir species in southern China suggests complex origin and genetic admixture

Fir species are mainly distributed across the high latitudes, preferring cold climates. The phylogeographic origins of those subtropical fir species that occur in low latitudes in southern China remain elusive, as does the nature of any inter-lineage hybridization. In fir species, mitochondrial DNA (mtDNA) is maternally inherited and chloroplast DNA (cpDNA) is paternally inherited, and the genetic variations in the two make them particularly useful for examining species' hybridizations and evolutionary histories. We sequenced four DNA fragments: two of mtDNA and two of cpDNA for 161 individuals from four subtropical endangered fir species (Abies beshanzuensis, Abies ziyuanensis, Abies yuanbaoshanensis, and Abies fanjingshanensis) and two more northerly distributed ones (Abies recurvata and Abies fargesii) from central and southwest China. Three mitotypes and four chlorotypes were recovered from the four southern species. In most populations, individuals share a single fixed mitotype and chlorotype. Three mitotypes clustered into two distinct clades, each associated with one of the northern species examined. For four chlorotypes, one occurred in A. ziyuanensis, A. beshanzuensis, A. fargesii, and A. recurvata, another in A. ziyuanensis and A. recurvata, the remaining two differed from others by two mutations exclusively in A. fanjingshanenis and A. yuanbaoshanensis. Phylogeographic origins of the subtropical fir species are complex, and genetic admixtures occurred during the evolutionary history of A. ziyuanensis. The genotyped populations further provide basic frames for genetic delimitation and effective conservation of these endangered species in the future.