| The biogeographic barrier has been considered as a driving factor of biodiversity.It forms a physical barrier to the flow of genes by preventing the movement of individuals,which leads to the increase of biological species differentiation and diversity.Species with different biological habits and habitat requirements have different responses to the isolation effect of geographical environmental factors.In this study,we selected Niviventer confucianus,a mountain species widely distributed in China,and Apodemus agrarius,which is widely distributed in farmland and low mountain areas,to conduct a comparative study to explore the isolation effects of different environmental factors on these two different Rodent species with different habitat requirements.This is of great significance for studying the influence of geographical isolation factors on species phylogeny and geographical genetic differentiation,as well as understanding the isolation mechanism of two species.In this study,the Cytb gene sequence of the mitochondrial genome was determined based on the N.confucianus and A.agrarius collected from several years of field investigation.The study downloaded all Cytb sequences of N.confucianus and A.agrarius with the geographical location record information of sampling points in GenBank.By constructing a phylogenetic tree and calculating genetic distance,based on the Cytb molecular species identification technology to ensure the correct classification and identification of species,different clades were obtained according to the phylogenetic tree.Extract the environmental factor data of the DEM,slope,vegetation type,land use type of each collection point in the geographic information system(GIS)and calculate the geographic distance between the two collection points and construct the least cost distance(LCD).Calculate the Kimura two-parameter genetic distance(K2P)for the specimens of each collection point,and analyze the correlation between the genetic distance and the geographical distance and the least cost distance between the different clades of the N.confucianus and between the N.confucianus and A.agrarius.It reveals the differences in the isolation effect of environmental factors on N.confucianus clades and N.confucianus and A.agrarius with different habitat type through intraspecific and interspecific comparison.It finds out the difference in geographical isolation of each environmental factor on the two different life types of the N.confucianus and A.agrarius species,in order to explore the intraspecific and interspecific geographic isolation mechanism and environmental factors of these two species.The main results are as follows.1.The results of the phylogenetic tree show that N.confucianus was divided into three clades,each with a different distribution area;A.agrarius was divided into two clades,but one of the two clades of the latter is a locally isolated group with a small distribution range.2.Among the three clades of N.confucianus,two of them(A,B)are genetically differentiated in accordance with the IBD(isolation by distance)pattern,and the other clade(C)is due to its distribution area(Hengduan Mountains)Overly complex terrain and diverse environments do not conform to the IBD pattern.The genetic differentiation of A.agrarius conforms to the distance isolation pattern.3.The suitable habitat analysis results of the MaxEnt model show that the suitable habitat of N.confucianus is steep slope(6-40°),high altitude(1400-3000m),forest,shrub and grass habitats(forest,shrub,grassland),and A.agrarius has a gentle slope(4-16°),low altitude(0-600m),forest and grass habitats(forest,grassland),indicating that N.confucianus is a mountain-type species,and A.agrarius is a plain-type species.4.The analysis of the relationship between LCD(Least Cost Distance)and genetic differentiation based on habitat suitability shows that habitat suitability is geographic isolation factor which affects A and B clades of N.confucianus,N.confucianus and A.agrarius.In the correlation analysis based on a single environmental factor and genetic differentiation,DEM,slope,vegetation types,land use types and rivers all have an impact on the genetic differentiation of A?B clades of N.confucianus,N.confucianus and A.agrarius.These are also isolation factors that affect the intraspecific and interspecific differentiation of the N.confucianus and A.agrarius.The clade C of N.confucianus is distributed around the Hengduan Mountains,so its geographical isolation has no significant regularity.5.The results of multiple regression analysis showed that among the environmental isolation factors of clade A,only DEM had a significant impact on geographic genetic differentiation,reflecting the large regular changes in altitude within its distribution area.The degree of geographical genetic differentiation of clade B is all related to the five environmental factors of DEM,slope,vegetation type,land use type and river,reflecting the balanced influence of environmental factors in the distribution area.There is no significant correlation between the geographic genetic differentiation of clade C and all five types of environmental factors.The geographic genetic differentiation of N.confucianus is significantly related to all five environmental factors,but slope and land use type have no significant influence on the geographic genetic differentiation of A.agrarius.The difference in the effects of these two environmental factors indicates that the plains and single agricultural land can isolate the spread of N.confucianus,but has no effect on A.agrarius.The results of this study indicate that the plain area is the geographic barrier of the geographic genetic differentiation of N.confucianus,which determines the differentiation of this species into species and the differentiation of intraspecies clade,while the A.agrarius is isolated by high mountains on the contrary. |
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