Genetic diversity and population structure of Distylium chinense revealed by ISSR and SRAP analysis in the Three Gorges Reservoir Region of the Yangtze River, China

Abstract

Distylium chinense is a dominant native evergreen shrub or small tree in the riparian forests in the Three Gorges Reservoir zone in China. The genetic diversity and population structure of D. chinense within and among eight populations was analyzed by ISSR (Inter Simple Sequence Repeat) and SRAP (Sequence-Related Amplified Polymorphism) markers. A high level of genetic diversity was observed at the species level (H = 0.3465, I = 0.5039 in ISSR; H = 0.1924, I = 0.4123 in SRAP) and at the population level (H = 0.3047, I = 0.4471 in ISSR; H = 0.1543, I = 0.3415 in SRAP). The genetic differentiation among population (Gst = 0.1205, Nm = 1.8247 in ISSR and Gst = 0.1976, Nm = 1.015 in SRAP) indicated low levels of genetic variation among populations and high levels of genetic polymorphism within populations. AMOVA (Analyses of molecular variance) also suggested that the main source of variation was within populations (93.9% in ISSR and SRAP in 81.9%). UPGMA (Unweighted Pair Group Method with Arithmetic means) cluster analysis and PCA (Principal Component Analysis) based on ISSR and SRAP amplification showed that populations from the same or adjacent regions were classified together. However, Mantel's test demonstrated that there was no significant correlation between the genetic distance and the geographical distance of each population (P > 0.05). Thus, the declining status of this species is likely due to the destruction of natural habitats, anthropogenic activities and overharvesting, rather than a loss of genetic diversity.