| Among the disjunct distribution patterns of the Northern Hemisphere,the disjunction between East Asia and the Mediterranean has been less concerned,especially for the plant groups with fossils far outside their current distribution.It is well known that fossils have impact on both time estimation and biogeographical history.The plant group would present quite complicated temporal and spatial evolutionary processes when inclusion of fossils outside its distribution.Pterocarya(Juglandaceae)contained eight species and disjunctly distributed in East Asia and the Mediterranean region.Interestingly,its fossils have been widely distributed in the subtropical and temperate regions of the Northern Hemisphere since the Paleocene.So far,there is few study to discuss the impact of fossil evidence on the disjunct distribution pattern of Pterocarya.In this study,the whole chloroplast genomes were used to reconstruct phylogenetic trees of all eight Pterocarya species.The divergent time was estimated by node dating(ND)and tip dating(TD)methods respectively,and the ancestral range reconstructions were inferred on S-DEC model.Finally,the maximum entropy model was used to predict the potential suitable distribution area of Pterocarya.This study integrated paleontological and phylogenetic data to explore the spatio-temporal evolutionary history of Pterocarya,and reveal the causes of disjunct distribution pattern of Pterocarya.The results also provide theoretical basis for plant protection under global climate change.The main results are as follows:1.The phylogenetic relationships among Pterocarya have been resolved well.The results based on 79 chloroplast protein coding genes showed that the phylogenetic trees on maximum likelihood and Bayesian inference were highly congruent.The monophyly of Pterocarya was strongly supported.Pterocarya divided into two clades with high supporting value.2.The complex evolutionary history of Pterocarya has been revealed.The results of TD method(including 15 extinct species)showed that Pterocarya originated at the early Paleocene(58.61 Ma,95% HPD: 51.08–66.84)and diversified at the early Eocene(50 Ma),which is consistent with the fossil records.When inclusion of fossilss,the current distribution of Pterocarya was attributed to 9 dispersal,5 vicariant and 12 local extinct events at least.The results of ND method(including 5 fossil calibration points)showed that Pterocarya originated from the early Eocene(49.87 Ma,95% HPD: 49–50.87)and began to diversify at the early Miocene(17.26 Ma,95% HPD: 9.86–27.32).The current distribution was just attributed to one dispersal and one vicariant events without fossils.3.The North Atlantic Land Bridge and Bering Land Bridge played important roles in spatio-temporal evolutionary history of Pterocarya.During the early Eocene,ancestor of Pterocarya migrated from East Asia to North America via Bering Land Bridge,and then to Europe through the North Atlantic Land Bridge.With the close of Turgai Strait,Pterocarya dispersed westward into Europe and expanded into North America via Bering Land Bridge through the late Oligocene-early Miocene.During the late Eocene-early Oligocene and the late Miocene,drastically temperature decline caused the species extinct in high latitude and altitude regions of North America and most of Europe.While contemporarily the uplift of the Qinghai-Tibet Plateau provided refuges,and the Pterocarya survive in East Asia.4.The suitable distribution areas of eight Pterocarya species in the future varied.The results of ecological niche modelling showed that under three climate scenarios(SSP1-2.6,SSP2-4.5 and SSP5-8.5)in 2070,the potential suitable distribution areas of P.fraxinifolia and P.stenoptera will expand,while the potential suitable distribution areas of the other six species(P.delavayi,P.hupehensis,P.insignis,P.macroptera,P.rhoifolia and P.tonkinensis)will contract.Minimum temperature of coldest month(bio6)is the main variable factor for P.fraxinifolia.In contrast,precipitation of warmest quarter(Bio18)is the main variable factor in determining the distribution of the remainders. |
