title: Late Pleistocene climate change promoted divergence between Picea asperata and P. crassifolia on the Qinghai-Tibet Plateau through recent bottlenecks.
abstract: Divergence during the early stage of speciation can be driven by a population bottleneck via reduced gene flow and enhanced lineage sorting. In this study, we aimed to examine whether such bottlenecks occurred during the initial speciation of two closely related spruce species Picea asperata and P. crassifolia occurring on the Qinghai-Tibet Plateau (QTP). We analyzed sequences of three chloroplast, two mitochondrial DNA fragments and a further 13 nuclear loci from 216 individuals of the two species. Both species showed a low level of genetic diversity in contrast to other congeners occurring in the QTP and adjacent regions. The estimated population sizes of P. asperata and P. crassifolia are less than the ancestral population size before splitting. These results together with multiple statistical tests (Tajima's D, Fu and Li's D* and F*) suggest that these two species underwent recent bottlenecks. Based on approximate Bayesian computation (ABC), we also determined that the period of the population shrinkage was consistent with the interspecific divergence during the late Pleistocene. The reduced population sizes and the divergent selection may together have triggered the initial divergence under high gene flow between these two species. Our results therefore highlight the importance of climatic oscillations during the late Pleistocene in promoting speciation through changing demographic sizes of the ancestral species on the QTP and in adjacent regions.
authors.affiliation: MOE Key Laboratory for Bio-resources and Eco-environment College of Life Sciences Sichuan University Chengdu 610065 China.
authors.forename: Hao
authors.initials: H
authors.lastname: Bi
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem College of Life Sciences Lanzhou University Lanzhou 730000 China.
authors.forename: Wei
authors.initials: W
authors.lastname: Yue
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem College of Life Sciences Lanzhou University Lanzhou 730000 China.
authors.forename: Xi
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem College of Life Sciences Lanzhou University Lanzhou 730000 China.
authors.forename: Jiabin
authors.initials: J
authors.lastname: Zou
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem College of Life Sciences Lanzhou University Lanzhou 730000 China.
authors.forename: Lili
authors.initials: L
authors.lastname: Li
authors.affiliation: MOE Key Laboratory for Bio-resources and Eco-environment College of Life Sciences Sichuan University Chengdu 610065 China; State Key Laboratory of Grassland Agro-ecosystem College of Life Sciences Lanzhou University Lanzhou 730000 China.
authors.forename: Jianquan
authors.initials: J
authors.lastname: Liu
authors.affiliation: MOE Key Laboratory for Bio-resources and Eco-environment College of Life Sciences Sichuan University Chengdu 610065 China; Key Laboratory of Tropical Forest Ecology Xishuangbanna Tropical Botanical Garden Chinese Academy of Sciences Mengla 666303 China.
authors.forename: Yongshuai
authors.initials: Y
authors.lastname: Sun
keywords: Bottlenecks; Picea; Pleistocene climate change; Qinghai–Tibet Plateau; species divergence