Divergent mechanisms of reduced growth performance in Betula ermanii saplings from high-altitude and low-latitude range edges

The reduced growth performance of individuals from range edges is a common phenomenon in various taxa, and considered to be an evolutionary factor that limits the species’ range. However, most studies did not distinguish between two mechanisms that can lead to this reduction: genetic load and adaptive selection to harsh conditions. This study investigated the climatic and genetic factors underlying the growth performance of Betula ermanii saplings transplanted from 11 populations including high-altitude edge and low-latitude edge population using RAD-seq analysis.
For 11 B. ermanii populations in wide-latitude range of Japan, we estimated gene diversity, nucleotide diversity, the coefficients of linkage disequilibrium, genetic differentiation between populations, population structure as well as the relatedness coefficient from SNPs. As a result, the low-latitude edge population exhibited a high level of linkage disequilibrium, low genetic diversity, a distinct genetic composition from t...