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The role of reticulation in the rapid diversification of organisms is attracting greater attention in evolutionary biology. Evidence of genetic exchange between diverging taxa is reported frequently, although most studies fail to show how hybridization and introgression contribute to the adaptation and differentiation of introgressed taxa. Here, we report a population genomics approach to test the role of hybridization and introgression in the evolution of the Picea likiangensis species complex, which comprises four taxa occurring in the biodiversity hotspot of the Hengduan–Himalayan mountains. Based on 84,793 SNPs detected in transcriptomes of 82 trees collected from 35 localities, we identified 18 hybrids (including backcrosses) distributed within the range boundaries of the four taxa. Coalescent simulations, for each pair of taxa and for all taxa taken together, rejected several tree‐like divergence models and supported instead a reticulate evolution model with secondary contacts occurring during Pleistocene glacial cycles after initial divergence in the late Pliocene. Significant gene flow occurred among some taxa after secondary contact according to an analysis based on modified ABBA–BABA statistics that accommodated a rapid diversification scenario. A novel finding was that introgression between certain taxa can contribute to increasing divergence (and possibly reproductive isolation) between those taxa and other taxa within a complex at some loci. These results illuminate the reticulate nature of evolution within the P. likiangensis complex and highlight the value of population genomic data in detecting the effects of introgression in the rapid diversification of related taxa. [ABSTRACT FROM AUTHOR]

Population genetics data based on multiple nuclear loci provide invaluable information to understand demographic, selective, and divergence histories of the current species. We studied nucleotide variation at 13 nuclear loci in 53 populations distributed among four closely related, but morphologically distinct juniper species of the Qinghai-Tibetan Plateau (QTP). We used a novel approach combining Approximate Bayesian Computation and a recently developed neutrality test based on the maximum frequency of derived mutations to examine the demographic and selective histories of individual species, and isolation-with-migration analyses to study the joint history of the species and detect gene flow between them. We found that (1) the four species, which diverged in response to the extensive QTP uplifts, have different demographic histories; (2) two loci, Pgi and CC0822, depart significantly from neutrality in one species and Pgi, is also marginally significant in another; and (3) shared polymorphisms are common, indicating both incomplete lineage sorting and gene flow after species divergence. In addition, the detected unidirectional gene flow provides indirect support for the theoretical prediction that introgression should mostly take place from local to invading species. Our results, together with previous studies, underscore complex evolutionary histories of plant diversification in the biodiversity-hotspot QTP. [ABSTRACT FROM AUTHOR]