Analysis of genetic diversity and population structure in endangered Populus wulianensis based on 18 newly developed EST-SSR markers

Abstract

Populus wulianensis is an endangered tree species endemic to Shandong Province, China. Genetic diversity assessments represent the basis and a prerequisite for protecting endangered species. In our study, a total of 116 individuals of P. wulianensis from 4 extant populations (3 wild populations and 1 artificial population that covered the entire geographic distribution of the species) were analyzed using 18 expressed sequence tag-simple sequence repeat (EST-SSR) markers to assess their genetic diversity and population structure. The 18 EST-SSR markers had high levels of polymorphisms (PIC = 0.698), and 202 alleles were amplified. The present study revealed high genetic diversity at the population level (Na = 4.847, NR = 3.000, HS = 0.624, HE = 0.611, I = 1.114, and PPL = 98.6%) and the species level (HT = 0.741). Private alleles were detected in all four populations (including the artificial population JYS). Negative inbreeding coefficients (FIS<0) indicated that the populations of P. wulianensis produced too many heterozygotes due to outbreeding and that there might be a risk of outbreeding depression. The AMOVA results showed that 19.05% and 80.95% of the total variation occurred among and within populations, respectively. Obvious genetic differentiation between populations (FST = 0.191) and a high level of gene flow (Nm = 2.566) were detected, indicating that gene flow is not the main cause of genetic differentiation among populations. The results of UPGMA cluster analysis, PCoA and structure analysis (ΔK = 4) showed that the 4 populations were clustered into four groups and suggested that the natural population ZHS gave rise to the artificial population JYS. The genetic bottleneck analysis results suggested that three populations (ZHS, JXS and JYS) recently experienced bottleneck events. These genetic results are of great significance for scientifically formulating conservation strategies for endangered P. wulianensis.