Abstract:The spatial genetic structure (SGS) is an important part of evolutionary ecological and ecological genetic processes in natural populations of plants. The spatial distribution patterns of genetic variation of two closely related sympatric Castanea species, C. mollissima and C. henryi, were investigated using seven microsatellite loci. A total of 173 alleles were detected in the two species. According to the isolation by distance model, Sp-statistics were calculated based on Moran's I spatial autocorrelation coefficient and Fij kinship coefficient for the two species. The results showed that there were high polymorphism in each species with low genetic differentiation ( FST=0.051). However, the two species displayed significant difference of SGS in this sympatric population. Spatial genetic structure was detected in C. henryi up to 100 m, while that was not observed in C. mollissima. Moreover, the Sp-statistic values based on Fij, were 0.002 for C. mollissima and 0.018 for C. henryi. These results further supported that C. henryi had stronger spatial genetic structure than C. mollissima. The difference of SGS in C. mollissima and C. henryi can be explained by different seed characteristics, as C. mollissima was charactertized by three nuts per cupule while there was only one nuts per cupule for C. henryi. Therefore, the long-distance seed dispersal via gravity and animals was much more favored for C. mollissima than C. henryi, which reduced different SGS between the two species.
