Study On Population Genetic Structure And Phylogeographical Of Two Fir Species (Abies) In Central China

Quaternary glaciation is an important climate factor for the species distribution, differentiation and speciation. The repetition of glaciation and interglacial periods drives species continuously migrating and settling down:when the glaciation comes, they migrate, on the one hand, from high latitude to low latitude and from south to north, on the other hand, from high-altitudes to low altitudes; when the cold glaciation turns into warm interglacial periods, they come back to the high latitude and high altitude regions. The species contraction and expansion caused by this replacement and alternation of glaciation and interglacial periods have a deep effect on the species genetic structure and population differenciattion and variety.Abies chensiensis and Abies fargesii are one example of the "imprints" of this alternation process. We sequenced a cpDNA fragments (trnT-trnL5’exon, trnL5’exon-trnL3’exon, trnL3’exon-trnF,5’rpS12-rpL20) of these two fir species, which is2015bp in length.From381samples we detect51haplotypes, which contain20mutations and1insert. Among the51haplotypes obtained,6are shared by the two firs,17are unique to A. chensiensis and27are only found in A. fargesii and many of the haplotypes are unique to populations. The evolutionary relationships of these haplotypes were analyzed and haplotype H1was found to be the primitive type of the two firs; whereas, H2and H5were primitive in A. fargesii. Many population unique haplotypes were evolved from these primitive ones. Result of genetic diversity analysis showed that two fir species have high level of genetic diversity, and the level of A. fargesii is higher than A. chensiensis. The coefficient of population genetic diversity (Hs) of A. chensiensis was0.683and Abies fargesii was0.725. The haplotype diversity(Hd) of A. chensiensis and A. fargesii are0.284～0.921and0.553～0.800respectively, and nucleotide diversity(Pi) of them are0.00029～0.00164and0.00056～0.00106respectively, the average number of nucleotide differences(K) of A. chensiensis ranged from0.5790to3.2974and ranged from1.5316to2.1368in A. fargesii. Result of population analysis showed that A. chensiensis is secondary level of poplution differentiation, which is higher the low level of A. fargesii. Genetic differentiations among populations of A. chensiensis were0.244(Gst) and0.183(Nst), whereas that of A. fargesii were0.091(Gst) and0.187(Nst). AMOVA showed that the genetic variances among populations accounted for24.28%and9.09%in A. chensiensis and A. fargesii respectively, greater than the among-population ones in both firs. But the genetic variance among populations of A. chcnsiensis is greater than that of A. fargesii. The differentiation between this two firs is not much (V%=3.69). Significant difference between Gst (unordered alleles) and Nst (ordered alleles) was rejected by U-test, suggesting a lack of phylogeographical structure for the two firs, and the The result of neutral test and analysis of nucleotide mismatch distributions between the two cpDNA showed the two firs have not undergone an obvious expansion. Base on the discussion of the phylogeography of the two firs, we can conclude that when the Quaternary glaciation comes they not only migrated eastward to the warm plain but also expanded to the low altitude regions.