Geographic isolation causes low genetic diversity and significant pedigree differentiation in populations of Camellia drupifera, a woody oil plant native to China

Camellia drupifera is mainly distributed in southern China. Due to geographical isolation, the C. drupifera resources in Hainan Island are very different from those in mainland China. However, the genetic variation, differentiation and evolution of C. drupifera have not been revealed. In this study, 22 SRAP markers and 7 chloroplast sequences were used to determine the genetic variation and differentiation and infer the origin and evolutionary history of C. drupifera populations. The results showed that C. drupifera populations exhibit low genetic diversity and exhibit an obvious pedigree geographical structure with high genetic differentiation and low gene exchange. The phylogenetic tree and principal component analysis (PCA) showed that this differentiation was mainly due to separation of the Hainan Island and mainland populations. Geographical isolation and island effects caused the pedigree structure with large genetic differentiation and reduced genetic diversity. A STRUCTURE analysis revealed that the mainland populations have a single genetic background compared with the Hainan Island populations. The haplotype network showed that H17 was the original haplotype in Hainan Island and that the H41 haplotype was important in the expansion of C. drupifera from Hainan Island to mainland China. The haplotype historical dynamics revealed expansion of the Hainan Island populations. This comprehensive analysis suggests that C. drupifera originated in Hainan Island and expanded its range to mainland China. These results provide a scientific basis for the protection, development and utilization of C. drupifera resources and a good example of how geographic isolation and island effects can drive plant lineage differentiation.