Population structure and genetic variation in the genus Dipteronia Oliv. (Aceraceae) endemic to China as revealed by cpSSR analysis

The genus Dipteronia Oliv. endemic to central and southern China consists of two species, D. sinensis Oliv. and D. dyerana Henry, both of them are rare and endangered. In the present study, genetic variation in 17 populations of D. sinensis and four populations of D. dyerana was estimated using ten polymorphic chloroplast microsatellite loci (cpSSR). Forty-nine chloroplast haplotypes were identified from 204 individuals analyzed. Thirty-nine haplotypes were found in D. sinensis, while ten in D. dyerana. No haplotype was shared between the species. AMOVA analysis revealed that the majority of the genetic variation was partitioned among populations within D. sinensis (F _ST = 0.7980) and D. dyerana (F _ST = 0.654). Cluster analysis grouped the 21 populations into two groups according to their species delimitation. The populations of D. sinensis were further divided into two subgroups corresponding to their geographical distributions. Correlation analysis revealed significant correlation between geographical distance and genetic distance of these populations (r = 0.326, p < 0.01 for D. sinensis vs. r = 0.777, p < 0.05 for D. dyerana). Genetic structure of these populations and a calculated pollen-to-seed flow ratio of (3.2:1 vs. 0.6:1) within the species suggested that little gene flow has occurred among the populations over an extended period. Thus, it implies that the genus Dipteronia might have experienced a genetic bottleneck and limited expansion during its evolutionary history.