RAD-seq unravels local adaptation along a latitudinal gradient for the wild rice Zizania latifolia

Abstract

The rapid climate change poses considerable threat to biodiversity by constantly alter-ing species distribution, phenotypic variation and allele frequencies. Understanding the interplay between the climate and species phenotypic and genetic variation is thus cru-cial to inform conservation strategies. In this study, we investigated local adaptation of a widespread aquatic species in China, Zizania latifolia. We performed restriction-site associated DNA sequencing (RAD-seq) for 66 wild samples composed of 10 populations, two populations in each of the five major eco-geographical regions of China and 6 cultivated samples derived from three culti-vars found in central China. We assessed genetic diversity and structure, genetic-envi-ronmental association, and genome-wide association studies for the 60 wild samples. Low levels of genetic variability were found in the Z. latifolia populations rang-ing from HE = 0.08 to HE = 1.52. Population structure showed that samples belonged to two major groups, north and south clades, split along a temperature boundary. It was estimated that the two groups diverged during the 8.2kiloyear event and later experi-enced severe genetic bottlenecks with advancement of agriculture and increase in hu-man population some 2k years later. Landscape analysis using SNP and trait data showed that environment was more important in shaping the genetic structure than geography, but the combined effect of environment and geography explained >90% of both genetic and morphological varia-tion. Several loci were found to be correlated with environmental variables as well as morphological traits, most of which were annotated as retrotransposons. Considering the abundance of transposable elements in the Z. latifolia genome, differentiation and local adaptation was inferred to be partly driven by temperature-induced transposable elements activity.