Transcriptome-based analyses of adaptive divergence between two closely related spruce species on the Qinghai-Tibet Plateau and adjacent regions

Adaptive divergence of tree species can greatly improve the level of forest species diversity, and thus it maintains the healthy and stable development of forest ecosystems. The endemic species Picea asperata and Picea crassifolia belong to the genus Picea of family Pinaceae in China. The natural geographical distributions of the two closely related species are adjacent, but the habitats are slightly different. Previous studies show that the morphological traits between the two species are distinct, offing an excellent model for understanding the process of adaptive divergence among tree species. This study uses the natural populations of the two species as samples which are based on the reference transcriptome of Picea abies, and employes population transcriptome data and genetic diversity analysis methods to investigate the adaptive divergence of two species due to climate change during the Quaternary Period. The key genes involved in the adaptively divergent selection are identified and annotated. In addition, a variety of analytical methods are combined to elucidate the process of speciation, population genetic structure, and gene flow. The results deepen our understanding of the genetic mechanism of the species diversity in spruce, and these candidate genes we detected are of great value in improving important traits of the spruce.