Phylogeography And Landscape Genetics Study Of The Forsythia Suspense(oleaceae)

Despite its high number of endemic deciduous broad-leaved species in China’s warm-temperate zone, far less attention has been paid to phylogeographic studies in this region. Forsythia suspensa(Thunb.) Vahl(Oleaceae) is a deciduous shrub widely distributed in China’s warm-temperate zone with elevations of 300 m to2200 m above sea level. As a typical component of DBLF, F. suspensa exists in most distribution areas of current DBLF in China. Consequently, we selected F. suspensa as a model for inferring phylogeographical patterns in China’s warm-temperate zone to understand DBLF population dynamics in response to climate change.In this work,the phylogeographic history of Forsythia suspensa endemic to China’s warm-temperate zone was investigated to explore the effect of climate change during the Pleistocene on the distribution of this deciduous broad-leaved species in China.In this study, two chloroplast DNA(cp DNA) regions, one nuclear ribosomal DNA(nr DNA) region, and ecological niche models were used to examine the phylogeographical pattern of F. suspensa. Our specific objectives were to address the following questions:(i) what is the genetic structure of F. suspensa populations in China as revealed by cp DNA and nr DNA data; and(ii) how did the species response to the climatic oscillations during the Pleistocene.The cp DNA data revealed seven phylogeographical groups corresponding to geographical regions. By contrast, the nr DNA data supported the samples clustered into three groups, which was inconsistent with separate geographical regions supported by cp DNA data. Ecological niche modeling showed that the climatically suitable area during the cold period was larger than that during the warm period.Both molecular data and ecological niche modeling indicated that F. suspensa expanded to nearby low-elevation plains in the glacial periods, and retreated to mountaintops during interglacial warmer stages. This study thus supported that F.suspensa persisted in situ during the glacial of the Pleistocene with enlarged distribution area, contrary to the hypothesis of long distance southward migration or large-scale range contraction.Identification of genetic diversity and genetic structure patterns is fundamentallyimportant for species effective management and conservation. This study used nine microsatellite loci to investigate the genetic diversity and structure of F. suspensa.Our findings revealed that the genetic diversity of F. suspensa(HT = 0.721) was lower than that of other seed plants in China and was particularly affected by over-harvesting its fruits. Microsatellite data also demonstrated a significant population differentiation within F. suspensa(FST = 0.113, P < 0.001). Mantel’s test and redundancy analysis indicated that geographical distance and temperature significantly contributed to the population genetic differentiation of F. suspensa.Bayesian analysis of the population structure suggested that F. suspensa could be divided into two genetic groups. Ecological niche models indicated that the two groups were isolated by the area with low climatic suitability. Based on the genetic information of F. suspensa, we propose populations with a high level of genetic diversity and high number of rare alleles to be prioritized for conservation.