Spatial genetic structure in natural populations of Phragmites australis in a mosaic of saline habitats in the Yellow River Delta, China

Abstract

Determination of spatial genetic structure (SGS) in natural populations is important for both theoretical aspects of evolutionary genetics and their application in species conservation and ecological restoration. In this study, we examined genetic diversity within and among the natural populations of a cosmopolitan grass Phragmites australis (common reed) in the Yellow River Delta (YRD), China, where a mosaic of habitat patches varying in soil salinity was detected. We demonstrated that, despite their close geographic proximity, the common reed populations in the YRD significantly diverged at six microsatellite loci, exhibiting a strong association of genetic variation with habitat heterogeneity. Genetic distances among populations were best explained as a function of environmental difference, rather than geographical distance. Although the level of genetic divergence among populations was relatively low (F'(ST) =0.073), weak but significant genetic differentiation, as well as the concordance between ecological and genetic landscapes, suggests spatial structuring of genotypes in relation to patchy habitats. These findings not only provided insights into the population dynamics of common reed in changing environments, but also demonstrated the feasibility of using habitat patches in a mosaic landscape as test systems to identify appropriate genetic sources for ecological restoration.

Figure 1. Schematic map showing sampling localities and the tendency of soil salinity based on OK predictions.

Pie graphs show the frequency distribution of the 203(PaGT9) homozygote and other allelic phenotypes in different populations.

Figure 2. Correlation between soil salinity and population genetic diversity in YRD.

Values of the observed number of alleles (A _o), allelic phenotypes (P _o), and the allele phenotype diversity statistic (H’) of each population are mean values over six microsatellite loci.

Figure 3. Estimated population structure for common reed from STRUCTURE analysis.

(A) Plot of the log probability of the data [LnP(D)] given values for K from 1 to 7. Circles represent the likelihood values of 5 replicate runs at each K value. (B) Population clustering for K = 2. Each individual is represented by a thin vertical line, which is partitioned into K coloured segments that represent the individual’s estimated membership fractions. Black lines separate individuals from different sampling sites, which are labelled below the figure.

Figure 4. Correlation between the frequency of the 203(PaGT9) homozygote and soil salinity, showing the increasing tendency of the 203(PaGT9) homozygote in populations inhabiting saline habitats in YRD.