Distributional dynamics and interspecific gene flow in Picea likiangensis and P. wilsonii triggered by climate change on the Qinghai-Tibet Plateau

AimTo address whether climate changes have altered the distributional ranges of cold-preferring conifer species, and whether this has influenced interspecific divergence. LocationQinghai-Tibet Plateau (QTP), Asia. MethodsWe obtained DNA sequences at 13 nuclear loci in 229 individuals collected from 32 populations across the range of two cold-preferring alpine species, Picea likiangensis and Picea wilsonii. Bayesian skyline plots (BSPs) were used to examine historical changes in effective population sizes. Species distributions were reconstructed based on presence-only data at 134 locations and climate variables from the WorldClim database, and the reconstructed distributions were compared with projected palaeodistributions at the Last Glacial Maximum (LGM, about 20ka). Four models of interspecific gene flow during the Pleistocene and Holocene were compared using approximate Bayesian computation (ABC). ResultsThe effective population sizes of P.likiangensis and P.wilsonii increased continuously from 5 to 0.2 Ma, but decreased after 0.2Ma. The distributional ranges during the LGM were wider than at present, confirming the trend of a recent decrease. However, the overlapping area became greater due to their shifted distributions, and these shifts altered the major direction of continuing interspecific gene flow. Main conclusionsThe early increase in the distributions of these two species might have been triggered by enlargements of the available cold habitats brought about by QTP uplift and Pleistocene glaciations. However, the distributional ranges decreased in response to climatic warming since the end of the largest glaciation. These distributional changes further retarded the process of differentiation by altering the pattern of gene flow. Our results shed light on the evolutionary complexity of alpine species in response to climate changes in this climate-sensitive biodiversity hotspot.