Genetic diversity and population structure of the endangered plant Salix taishanensis based on CDDP markers

Abstract

Salix taishanensis, belonging to family Salicaceae, is a rare tree species endemic to China. This species is at risk of extinction because of continued habitat disturbance. However, the genetic diversity of the natural populations has not been assessed to date. By using conserved DNA-derived polymorphism marker techniques, we studied the genetic diversity and population structure of four populations of Salix taishanensis. A total of 128 discernible loci were obtained from 115 individuals using 13 primers, and 73.44% of the loci were polymorphic. Nei’s genetic diversity index (H) was 0.2227, and the Shannon diversity index (I) was 0.3505, indicating that the genetic diversity in Salix taishanensis is low. At the population level, the percentage of polymorphic loci (PPL) averaged 53.71%, H averaged 0.1932, and I averaged 0.2864. The highest level of genetic diversity was observed in the Pangquan Valley (PQG) population (PPL = 58.59%, H = 0.2040, I = 0.3044); the lowest was observed in the Mount Tai (MT) population (PPL = 49.22%, H = 0.1808, I = 0.2680). Analysis of molecular variation (AMOVA) revealed significant genetic differentiation within and between populations (P < 0.001), with 79.71% of the variation occurring among populations and 20.29% occurring within populations. Genetic variation analysis showed a coefficient of gene differentiation of 0.1723 and a gene flow value of 2.4014 among populations. A Mantel test and cluster analysis revealed no significant correlation between genetic distance and geographic distance among populations (r = −0.3189, P = 0.7083). The 115 individuals were divided into four genetic clusters according to Bayesian structure and principal coordinate analysis (PCoA), correlating significantly with geographic distribution. The low-level genetic diversity and obvious population differentiation of the S. taishanensis populations may be related to their evolutionary histories and geographical isolation. If protective measures are not taken in time, their genetic diversity will continue to decrease due to inbreeding effects. These results will assist with the formulation of conservation strategies based, such as genetic rescue and in situ and ex situ conservation.