Study On Gene Introgression Of Abies Fargesii Var. Fargesii And Abies Fargesii Var. Faxoniana

Many studies have shown that in the process of population expansion during interglacial period, populations which come from different spectrum branch of shelter and obvious genetic differentiation produced gene introgressive after secondary contact in some suture zone. Gene introgression is a phenomenon that refers a species of genetic material across the species barriers transferred into another species, which is very common in plants. Gene introgression can produce a new gene combinations and ecotype which would help the species to better adapted to the ecological environment by strengthening the species diversity, promoting of species distribution and expansion population.We found Abies fargesii var. fargesii and Abies fargesii var. faxoniana overlapping distribution in the transition area between the north of Sichuan province and the south of Gansu province in China, and some populations appeared the traits of individuals. It will be the hybrid individuals of Abies fargesii var. fargesii and Abies fargesii var. faxoniana? Two maternally inherited mitochondrial DNA fragment (ATPA and ATP8), three paternally inherited chloroplast DNA fragments (trnT-trnL, trnL-trnL, trnL-trnF and rpS12-rpL20) was used to determined 13 Abies fargesii var. fargesii populations and 9 Abies fargesii var. faxoniana populations, a total of 512 individuals. We detected 15 variable sites in mitochondrial DNA sequences, a total of 15 mitochondrial haplotypes and 37 variable sites in chloroplast DNA sequences, a total of 51 haplotypes. All these information would contribute to further explore genetic diversity and genetic differentiation analysis, and to identify the geographical distribution of haplotype patterns and phylogenetic relationships.(1)The mitochondrial DNA analysis of populations genetic structure showed that: the genetic differentiation between groups coefficient is higher and gene flow is lower, (GST=0.782、Nm=0.0677 for A. fargesii var. fargesii,GST=0.801、Nm=0.0597 for A. fargesii var. faxoniana),hierarchical structure is clear (Nst>Gst,P<0.05). Four distinct geographical regions have their own unique haplotypes. The AMOVA analysis reveals that the genetic variation mainly exists among populations. Four mitochondrial haplotypes shared by the two Abies, Hmtl and Hmt7 were common to both species which may be caused by gene introgression. (2)The population genetic structure of chloroplast DNA analysis showed that: the genetic differentiation between groups coefficient is lower and gene flow is higher. (GST=0.080、Nm=0.6403 for A. fargesii var.fargesii, GST=0.185、Nm=0.2442 for A. fargesii var. faxoniana). There was no significant difference between the NST and GST, so populations were lack of apparent phylogeographical structure. It is probably because the chloroplast DNA goes through long distance spread pollen so that the differentiation between populations is not obvious. The AMOVA analysis reveals that the genetic variation mainly exists among individuals.Hcpl and Hcp5 were shared by the two Abies which was changed along with the geographic distance caused by gene introgression.Mismatch distribution analysis and neutral inspection results show that most of the populations have experienced the expansion. The "star shaped" structure in the network also confirmed that the population had expanded. We conclude that these populations were from different refuges, they expand rapidly and formed the secondary contact distribution pattern when temperature rapidly rises in the Quaternary interglacial. Due to long-term overlapping distribution, the gene introgressive happened to the two kinds of Abies, which was the reason of the intermediate character of the individual.