Phenotypic traits of 17 populations of Spartina alterniflora in China

Understanding the ecological and evolutionary processes that underlie
phenotypic and genetic variation among invasive plant populations and the
capacity of such populations to colonize a broad range of environments is
a major goal in ecology. Rapid adaptation to local environmental
conditions often leads to latitudinal clines in both phenotypes and
genotypes of invasive plant species. Previous studies suggest that natural
selection influenced a latitudinal cline in phenotypic traits of the
invasive plant Spartina alterniflora in China. However, little is
understood of the relationship between genetic and phenotypic
differentiation and environmental factors among S. alterniflora
populations. Here, we studied whether S. alterniflora exhibits a
latitudinal cline in genetic diversity across the east coast of China and
whether genetic and phenotypic differentiation among populations were
correlated with environmental factors. The Restriction-site Associated DNA
(RAD-seq) sequencing was used to obtained genomic information of 17
populations of S. alterniflora in China. A redundancy analysis (RDA) was
performed to assess whether environmental variables were corelated with
genetic and phenotypic differentiation among the populations. A univariate
environmental association analysis (implemented through Latent Factor
Mixed Model; LFMM) and a principal component analysis (PCAdapt) were used
to test for signature of local adaptation. A total of 3, 310 SNPs showed a
clear genetic structure among populations in three climatic regions
(northern, mid-latitude and southern). Positive correlations between
genetic differentiation and variation in reproductive characteristics of
S. alterniflora were revealed, suggesting that sexual reproduction traits
might be stable and genetically heritable. Outlier loci that were
identified by both PCAdapt and LFMM methods were significantly correlated
to soil phosphorus content, soil salinity, and precipitation. These
results provide evidence of molecular signatures of local adaptation of S.
alterniflora and suggest that rapid adaptive evolution may facilitate
invasiveness of S. alterniflora in China.