Phylogenomic and ecological analyses reveal the spatiotemporal evolution of global pines

How coniferous forests evolved in the Northern Hemisphere remains largely unknown. Unlike most groups of organisms that generally follow a latitudinal diversity gradient, most conifer species in the Northern Hemisphere are distributed in mountainous areas at middle latitudes. It is of great interest to know whether the mid-latitude region has been an evolutionary cradle or museum for conifers and how evolutionary and ecological factors have driven their spatiotemporal evolution. Here, we investigated the macroevolution of Pinus, the largest conifer genus and characteristic of northern temperate coniferous forests, based on nearly complete species sampling. Using 1,662 genes from transcriptome sequences, we reconstructed the first robust species phylogeny and re-estimated divergence times of global pines. We found that approximately 90% of extant pine species originated in the Miocene in sharp contrast to the ancient origin of Pinus, indicating a Neogene re-diversification. Surprisingly, species at middle latitudes are much older than those at other latitudes. This finding, coupled with net diversification rate analysis, indicates that the mid-latitude region has provided an evolutionary museum for global pines. Analyses of 31 environmental variables, together with a comparison of evolutionary rates of niche and phenotypic traits with net diversification rate, found that topographical heterogeneity played a primary role in pine diversification, and the aridity index was decisive for the niche rate shift. Moreover, fire has forced diversification and adaptive evolution of Pinus. Our study highlights the importance of integrating phylogenomic and ecological approaches to address evolution of biological groups at the global scale.