Comparative Analysis Of Population Genetic Structure In Abies Chensiensis And A. Fargesii Inferred From Microsatellite Markers

As the main forest species of the northern hemisphere, Abies is the second largest genus in Pinaceae except for pinus. According to statistics, there is a total of28species of Abies plants in China which has the largest number of fir distribution in the world. A.fargesii is an endemic widespread species in our country, its natural pure forest is widely distributed in the Qinling Mountains,Bashan Mountains and southeast Tibet Plateau,it al so is a dominant member of coniferous forest found at elevations from1900to3600m. A. chensiensis is the other endemic species, has been included in the checklist of State Protection Category Ⅱ in China. Its natural distribution is similar as A. fargesii. In recent years, due to environmental degradation and man-made destruction, a large area of A. chensiensis degraded,now it uaually found scattered in small forest fragments at elevations from1500to2300m.This study aims to have a comparative analysis of genetic diversity and population genetic structure in A. chensiensis and A.fargesii based on micrisatellite molecular markers method, for reveal the genetic variation within the populations and the genetic differentiation between populations, then inquire into the genetic impacts of habitat fragmentation on A. chensiensis. provide scientific evidence for the utilization and protection of the endangered species.To successfully develop16microsatellite primers by magnetic beads enrichment method and454high-throughput pyrosequencing,the16effective microsatellite sequence(Achl～Ach8、 Afal～Afa8) in the GenBank accession number is:KC505632～KC505639. KF312366～KF312373.A total of698individuals were collected from24populations of two firs, We picked7pairs of microsatellite primers(Achl、Ach2、Afa2、Afa3、Afa4、Afa5and As09) to study on its population genetic structure. Seven locus had detected94polymorphic alleles in total,with the range of14to29per locus. For A. chensiensis, the number of alleles per locus ranged from8to22, with an average of14.1. The observed and expected heterozygosities ranged from0.345to0.894and from0.388to0.872, respectively.For A.fargesii, the number of alleles per locus ranged from14to28, with an average of18.4. The observed and expected heterozygosities ranged from0.225to0.916and from0.261to0.885, respectively. Genetic diversity estimates from seven SSR loci at population level are also summarized. For A. chensiensis, the number of alleles per locus ranged from5.3to10.4, with an average of8.3. The observed and expected heterozygosities ranged from0.629to0.743and from0.671to0.78, respectively. And for A. fargesii, the number of alleles per locus ranged from8to12.6, with an average of10.3. The observed and expected heterozygosity ranged from0.597to0.705and from0.707to0.81, respectively.The inbreeding coefficient of two firs is0.097and0.127, respectively. Statistics indicate that the genetic diversity of A. fargesii is slightly higher than A chensiensis.In the comparison of genetic differentiation level reflected in Fst, A. chensiensis (Fst=0.0634) is larger than in A. fargesii (Fst=0.035).Compared to A. chensiensis (Nm=5.581), more frequent gene flow between populations (Nm=10.977) in A. fargesii slowed the level of genetic differentiation between populations. High estimated gene flow is consistent with the results that there is not significant correlation between genetic and geographical distances (r=-0.0168, p=0.5730for A chensiensis, and r=-0.1866, p=0.9670for A, fargesii).The results of Bottleneck test indicated that all populations of two firs have not experienced a bottleneck effect. AMOVA analysis revealed that most of the genetic variability detected was contained within populations, variation between populations was only6.34%in A. chensiensis and3.49%in A. fargesii. The analysis also detected that there is only2.1%of the variation resided between species.Both A. chensiensis and A. fargesii maintain a high level of genetic diversity and low level of genetic differentiation, and most of the genetic variation occur within populations. For A chensiensis, relatively low genetic diversity and relatively high level of genetic differentiation between populations indicated that habitat fragmentation has a negative effect on its reproduction.