| The spatial distribution pattern of population genetic diversity is affected by the current distribution of species and past climate change.According to the center periphery hypothesis(CPH),the genetic diversity of the population in the geographical center of species distribution is high,while that of the population in the geographical edge is low,while the climate factors are not considered.Climate change since the last glacial maximum(LGM)has had an important impact on the distribution of animals and plants in the northern hemisphere.In China,LGM has caused great differences in temperature and precipitation between the South and the north,resulting in the retreat of temperate forests to 25-30 degrees north latitude.Betula albosinensis belongs to the costatae group of subgenus Betula.It is a tetraploid species with monoecious and wind pollination.It is widely distributed in the alpine areas with high altitude,abundant water and moist soil in China.It is a cold resistant plant and pioneer species in temperate forests,and has important ecological and use value.In this study,red birch was selected as the research species to investigate its distribution and living environment in China,and a large number of samples were collected and longitude and latitude information was recorded.Microsatellite markers were used to analyze the genetic diversity.Based on the niche model(ENM)and birch pollen records,the suitable habitats of red birch in LGM,middle Holocene(MID),present and future(2070)were inferred.The distance between population and geographical center,geographical edge and southern edge were calculated to represent the current distribution variables of species.The distance from niche center,current climate suitability,climate stability and climate variability were calculated to represent climate variables.In addition,the population genetic mixing was calculated.Six models related to population genetic distribution were established by using the above eight variables.Based on the above research methods,this paper explored whether red birch had adaptive evolution,and then revealed the effects of current distribution location,climate change and genetic mixing on the spatial distribution pattern of population genetic diversity.The main results are as follows:1.The population of B.albosinensis had adaptive evolutionIn this study,815 individuals of 37 populations were used to carry out microsatellite molecular markers.The results of cluster analysis using structure and PCo A showed that the population of red birch had genetic differentiation,which could be divided into northern cluster including Qinling Daba Mountain and its northern and northwestern regions and southern cluster including Southwest Yunnan and southern Sichuan.ENM indicated that Sichuan Basin has not been a suitable habitat for red birch since LGM.Therefore,it may hinder the genetic exchange among red birch,which is part of the reason for the differentiation of North-South cluster.In addition,Qinling Daba Mountain has always been a high suitable area for red birch,which may act as a diffusion corridor in the process of red birch diffusion,so that there is no genetic differentiation in the population north of Qinling Daba Mountain and North China.At the same time,the diffusion corridor makes the seeds and pollen of red birch migrate southward,resulting in the genetic diversity in the northern region of high latitude is significantly higher than that in the southern region of low latitude.2.The current distribution position of the population determines its genetic distribution patternThrough analyzing the linear fitting relationship between the six spatial models and the genetic diversity parameters,it is found that the most important factor affecting the distribution of genetic diversity is the distance between the population and the geographical edge and the southern margin.At the same time,there was a certain correlation between population genetic diversity and the distance from the geographical center and edge,which indicated that the spatial distribution of population genetic diversity partly supported the central edge hypothesis.Although the survival conditions of red birch in the field have certain requirements on temperature and precipitation,the support rate of the model considering climate change is relatively small,which may be because the climate change during the glacial period has little influence on the seed and pollen dispersion of red birch.The ENM results show that the distribution area of red birch is relatively stable from LGM to the present.3.B.albosinensis has Cryptic refugia in the north of ChinaThe results of ENM showed that there were continuous suitable habitats for red birch in the north,southwest and southeast of China during LGM.Combined with the results that the genetic diversity of the population in the North was higher than that in the south,it was inferred that the past dynamics of red birch population was not simply retreating southward during the glacial period and expanding northward during the postglacial period,but there were hidden refuges in the north of China during LGM,There are multiple refuges in the southern part of China,and there is limited expansion from the geographical center to the surrounding areas in the post glacial period. |
