Population Genetic Structure And Gene Flow In The Seagrass Zostera Japonica (Zosteraceae) Along The Coastal Regions Of South China

As one of the three main ocean ecosystems, seagrass meadows have important ecosystem services. However, nowadays they are suffering from globally declining due to natural environment deterioration and human disturbance. Zostera japonica, a monoecious seagrass, is a common dominated species of seagrass beds. In this study, I screened12polymorphic loci for Z. japonica. Population genetic structure and genetic diversity of this species were clarified based on these loci. Furthermore, we tried to discern the roles of clonality and gene flow on genetic diversity in Z. japonica. The follwoings are three main conclusions:1. Using the method of biotin-streptavidin, we obtained12polymorphic micro satellite loci in Z. japonica. These loci had excellent repeatability and stability in PCR, providing a powerful tool to study population genetics for the species.2-10alleles per loci were found in57samples of two Z. japonica populations (BG and DJ) located in Hainan province. The number of mean alleles in BG and DJ were4.1and4.4, respectively. Ranges of observed and expected heterozygosities were0.0000-1.0000,0.0000-0.7983(BG) and0.0000-1.00,0.0000-0.8542(DJ).2. Among the12microsatellites loci,2loci (ZJ48and ZJ1368) were not neutral.251samples collected from8Z. japonica populations were genotyped using10neutral loci. The minimum clonal richness was0.742(YT) and the maximum was0.980(SZ); the expected heterozygosity ranged from0.373(YT) to0.621(DJ). The standard genetic differentiation coefficient (FSr) was0.354among all populations. Using Structure, PCoA and AMOVA, the8populations could be clustered into2groups:the western group (SX, DC, GS and JD) and the eastern group (BG, DJ, YT and SZ). There was a significant relationship between the shortest ocean surface distance and genetic distance, indicating an isolation-by-distance pattern. Gene flow within western group was larger than that of the eastern one, while gene flows within groups were larger than between groups. A genetic barrier was identified between populations YT and SZ.3. Clonal richness was high in Z. japonica, and selfing was absent within population. The clonal sub-range was5.1m. A significant difference in spatial genetic structure at the first distance class (0-1m) was observed between ramet-level and genet-level. The spatial genetic structure of ramet-level was much stronger than that of genet-level (ω=17.373, p=0.023). As distance increasing, difference in spatial genetic structure between the two levels decreased gradually. Dispersal variance of sexual reproduction (σ=3.18) was larger than that of clonal dispersal (σ=0.18), suggesting that clone growth was restricted and dispersal of long distance depended on sexual reproduction.