Comparative Phylogeography Of Fir Species In East Asia And North America

In this study,Abies chensiensis,Abies nephrolepis,Abies lasiocarpa and Abies balsamea were selected as the research objects,and they were divided into high-low elevation species pairs.Based on the results of species distribution models and integrating phylogeographical analyses,answer the response model of firs to Quaternary climate changes,and verify the climate response models of high-elevation and low-elevation species in different continents.By supplementing the molecular experiments of outgroups,answering the question of migration of Abies between East Asia and North America.The main research contents and conclusions are as follows:(1)In this study,four types of fir species,including high-elevation Abies chensiensis and low-elevation Abies nephrolepis in East Asia,and high-elevation Abies lasiocarpa and low-elevation Abies balsamea in North America,were screened as highelevation and low-elevation fir species pairs,The species distribution of these four species was simulated according to the loci information of these four species.The results show that all the four fir species conform to the hypothesis of “elevation shift” of the response model to Quaternary climate change.Whether in East Asia or North America,high-elevation firs experienced glacial expansion,and low-elevation firs experienced interglacial expansion.And Abies chensiensis and Abies lasiocarpa,two high-elevation firs,have experienced notable range expansions events.(2)In integrating phylogeographical analyses,we collected 4 species,44 populations and 585 individuals.Mitochondrial genes nad5-4 and chloroplast gene trn L-trn F were selected in the analysis of gene lineage.In species distribution modeling,we performed analyses based on 267 environmental variables at three different time points.The Mismatch distribution analyses based on cp DNA indicates that Abies chensiensis and Abies lasiocarpa detected notable range expansions events.The expansion time of Abies chensiensis is about 53.1 ~ 34.5 kya(g=25 years)or 26.6 ~ 17.2 kya(g=50),and the expansion time of Abies lasiocarpa is about 43.8~28.4kya(g=25)or 21.9~14.2 kya(g=50).The timing of the expansion event is highly consistent with the timing of the Last Glacial Maximum in East Asia and North America.The results of species distribution models in different time periods show that the optimal distribution areas of Abies chensiensis and Abies lasiocarpa are significantly larger in the glacial period(Last Glacial Maximum)than in the interglacial period(Last Interglacial and present),which is consistent with the results of Mismatch distribution analysis.while the optimum distribution area of Abies nephrolepis and Abies balsamea in interglacial period is obviously larger than that in glacial period,which is also consistent with the results of Mismatch distribution analysis.Combined with the distribution pattern of genetic diversity,various evidences indicate that Abies chensiensis and Abies lasiocarpa experienced glacial expansion and interglacial contraction in the “elevation shift” hypothesis,while Abies nephrolepis and Abies balsamea experienced glacial contraction and interglacial expansion.(3)In the face of continued global warming,the endangered firs will face severe habitat shrinkage or endangerment due to insufficient elevation space for upward migration to cope with future warming.The most helpful and urgent strategy is to move to more suitable areas for ex-situ conservation.For the five critically endangered firs in China and Vietnam,the southern part of the Hengduan Mountains has been a suitable and ideal habitat throughout the Quaternary period.In addition,there are more than 35 National Botanical Reserves in the Hengduan Mountains,and breeding programs can be carried out in the specific garden,which is of great significance in ex-situ conservation.