GENETIC DIVERSITY OF DIFFERENT GEOGRAPHICAL POPULATIONS IN Solen strictus REVEALED BY ISSR MARKERS

The razor shell Solen strictus is a member of family Solenidae (Veneroida) bivalve. The Solen strictus distributes widely along the coasts of the Bohai Sea and the Yellow Sea in China, where is a commercial important and potential mariculture species. In this study, genetic diversity in five different geographical populations of the Solen strictus were analyzed by the Inter-Simple Sequence Repeat (ISSR) markers. The samples of the five populations were taken from the off-shores of Dalian (DL), Yantai (YT), Laizhou (LZ), Qingdao (QD) and Ganyu (GY), respectively. The objectives of present study are: 1) use clear amplified ISSR fragments to examine the genetic variation within and among populations of Solen strictus; 2) lay a foundation of selecting the parent Solen strictus for artificial propagation.Total genomic DNA was extracted from vivisectional foot muscle of two-year-old Solen strictus with standard method. DNA samples were stored at ?20 ℃ until use. The ISSR primers were made by Sangon Inc. (Shanghai, China), and we used 13 primers which were screened from 30 primers. PCR amplification reaction was carried out in a 25 μL mixture that included 1 × PCR buffer, 2.5 mM of MgCl2, 0.25 mM of dNTP, 0.5μM of primer, 1 unit of Taq DNA polymerase, and approximately 40 ng of template DNA. The PCR cycling conditions were: preamplification denaturation at 94 ℃ for 5 min followed by 45 cycles, each cycle included 45s denaturation at 94 ℃, 45s annealing at 52 ℃, 90s extension at 72 ℃, and then a final extension at 72 ℃ for 10 min, amplified products resolved by electrophoresis in 1.5% agarose gels.Genetic parameters were calculated by using software POPGENE (version 1.32) that included percentages of polymorphic loci, observed number of alleles, effective number of alleles, Nei’s gene diversity, Shannon’s information index, genetic differentiation coefficient (Gst), gene flow (Nm) and Nei’s unbiased genetic distances. The genetic variation within and among populations of the Solen strictus was estimated by an analysis of molecular variance (AMOVA) using software WINAMOVA (version 1.55). The dendrogram was constructed on Nei’s unbiased genetic distance and neighbor-joining (NJ) cluster analysis which was determined for the five populations and the 100 individuals from these populations by software MEGA (version 4.0), respectively. The Mantel test was taken for correlation between genetic and geographic distance with software TFPGA (version 1.3).The results showed that total of 200 loci from five populations were amplified with 13 primers, average 15.4 loci each primer. The proportion of polymorphic loci in the five populations ranged from 43.56 % to 60.43 %. The Nei’s gene diversity and Shannon’s information index of Solen strictus was 0.2854 and 0.4390 at species level, 0.1674 and 0.2530 at population level, respectively. NJ cluster analysis indicated that QD population and GY population were the nearest in genetic relationships, and the genetic distance between YT population and other four populations were farther. There was no correlation between genetic and geographic distance among the five populations studied by the Mantel test (r = ?0.0834, P > 0.1). The AMOVA demonstrated that the among-population component accounted for 47.71 % of the total variation, while the within-population component accounted for 52.29 %. The within-population genetic variation was apparently larger than the among-population. The genetic differentiation coefficient (Gst) and the gene flow (Nm) were 0.2889 and 1.3194, respectively among the five populations.These data indicates that the genetic diversity of Solen strictus is relatively high, and there is genetic differentiation of some extent among the five populations of Solen strictus. The genetic differentiation among populations could be attributed to the limited remotion and the discontiguous habitat. Anyhow, the results of above research will be helpful for the conservation and utilization of resources, and provide a basis for artificial propagation of Solen strictus.