Evolutionary radiation of the Eurasian Pinus species under pervasive gene flow.

Evolutionary radiation, a pivotal aspect of macroevolution, offers valuable insights into evolutionary processes. The genus Pinus is the largest genus in conifers with 90% of the extant species emerged in the Miocene, which signifies a case of rapid diversification. Despite this remarkable history, our understanding of the mechanisms driving radiation within this expansive genus has remained limited. Using exome capture sequencing and a fossil-calibrated phylogeny, we investigated the divergence history, niche diversification, and introgression among 13 closely related Eurasian species spanning climate zones from the tropics to the boreal Arctic. We detected complex introgression among lineages in subsection Pinus at all stages of the phylogeny. Despite this widespread gene exchange, each species maintained its genetic identity and showed clear niche differentiation. Demographic analysis unveiled distinct population histories among these species, which further influenced the nucleotide diversity and efficacy of purifying and positive selection in each species. Our findings suggest that radiation in the Eurasian pines was likely fueled by interspecific recombination and further reinforced by their adaptation to distinct environments. Our study highlights the constraints and opportunities for evolutionary change, and the expectations of future adaptation in response to environmental changes in different lineages.