Genetic Divergence and Evolutionary Adaption of Four Wild Almond Species (Prunus spp. L.)

Abstract

Parallel evolution usually occurs among related species with similar morphological characters in adaptation to particular environments. Four wild almond species (Prunus) sharing the character of dry mesocarp splitting are distributed in China, most of which occur in arid Northwestern China. In the present study, we aimed to clarify the phylogenetic relationship, evolutionary history, and environmental adaptation of these wild almond species based on genome-wide SNP data and chloroplast genomes. Chloroplast phylogeny showed P. pedunculata and P. tenella were clustered with wild cherry species (Prunus), while P. mongolica and P. tangutica were clustered with wild peach species (Prunus). Genomic phylogeny suggested P. tenella formed an independent clade. An ABC-RF approach showed P. pedunculata was merged with P. tenella and, then, diverged from the ancestor of P. mongolica and P. tangutica. P. tenella was split from other wild almond species at ca. 7.81 to 17.77 Ma. Genetic environment association analysis showed precipitation variables contributed the most to genetic variations between P. mongolica from an arid environment and P. tangutica from a humid environment. Finally, a total of 29 adaptive loci were successfully annotated, which were related to physiological processes in response to abiotic stresses. Inconsistent genomic and chloroplast phylogenetic positions of P. tenella suggested this species could have originated from historical hybridization among different clades of Prunus. Physiological mechanisms promoted P. mongolica in adapting to the arid environment in Northwestern China.