Genetic Diversity And Spatial Genetic Structure Among Breeding Populations Of The Saxaul Sparrow

Genetic diversity is the cornerstone of the survival of the species,and the level of genetic diversity reflects the evolutionary potential of the species.Population genetic diversity refers to the sum of genetic variation of all individuals in a population,and when genetic variation has a certain spatial distribution law among populations,it is considered to have interpopulation spatial genetic structure.The study of spatial genetic structure and its influencing factors between populations is the basis for discussing speciation and adaptive evolution,and also has important guidance for species conservation in patch environment.Our study took desert representative species Saxaul Sparrow（Passer ammodendri）as the research object,and samples were collected in area A（located in the southern part of Anxi Extremely Arid Desert National Nature Reserve,Gansu Province）from June to August 2020.A total of 693 samples were collected from 15 breeding populations within a radius of about 200km.By using the information of 14 microsatellite loci,the genetic diversity and spatial genetic structure of breeding populations were analyzed,and expound the gene flow between breeding populations with patch distribution,and explored the relationship between spatial genetic structure and dispersal.Through analysis,the research results are as follows,（1）Shannon’s information index of the Saxaul Sparrow breeding populations range from 1.650 to 2.010,gene diversity changes between 0.771～0.833.The expected heterozygosity were 0.726～0.818,average expected heterozygosity was 0.774.The genetic diversity index of each breeding population were similar,and high levels of breeding populations’diversity were observed.However,the number of effective alleles varied from 4.502 to 6.218,and the average effective number of alleles was5.352,which was much smaller than observed number of alleles（9.534）and was easy to be lost in gene transmission.Therefore,the risk of loss of gene diversity was high.The observed heterozygosity of each breeding population was lower than the expected heterozygosity,which indicated that there were more homozygous genotypes and less heterozygote genotypes in the breeding populations.The number of inbreeding coefficient(F_IS)fluctuated between 0.267 and 0.398.At the same time,except for 4microsatellite loci,the other 10 microsatellite loci deviated from Hardy-Weinberg equilibrium（ns）significantly for all breeding populations.These results indicated that there was a certain degree of inbreeding in breeding populations of Saxaul Sparrow.（2）The gene flow value（Nm）of the 15 breeding populations ranged from 8.831to 402.976.Gene flow between the breeding populations of Saxaul Sparrow was frequent,and the differentiation degree between breeding populations was very low.There was a high genetic identity（GI,0.774～0.973）and a small genetic distance（GD,0.028～0.257）among the breeding populations,the kinship of each breeding population was closed.The results of cluster analysis of all individuals showed that individuals in each breeding population were in a mixed state,and individuals could not be distinguished by breeding population unit,indicating that each breeding population of Saxaul Sparrow had a very high degree of genetic similarity.The results of AMOVA analysis of 15 breeding populations showed that the genetic variation between populations accounted for only 0.5%of the total genetic variation,but 71.32%of the genetic variation occurred within individuals（P<0.001）.The results of Nei’s gene differentiation coefficient were also consistent,and the average of genetic diversity（H_S,0.797）within the breeding population was close to the average of total genetic diversity（H_T,0.804）to a large extent.The results showed that the genetic variation mainly occurred within the breeding population and the differentiation degree among breeding populations was very low.（3）The results of spatial autocorrelation analysis showed that there was no spatial genetic structure among breeding populations of Saxaul Sparrow.With the extension of spatial linear distance,the genetic distance and spatial distance of the breeding populations of Saxaul Sparrow were not significantly correlated.Most microsatellite loci in each breeding population deviated from the Hardy-Weinberg equilibrium significantly,and the heterozygote genotypes were relatively few.However,the breeding population maintained high genetic diversity,and the genetic differentiation between populations was weak,with extensive gene flow and high genetic similarity.Previous studies have shown that individuals in the breeding population of Saxaul Sparrow tend to be closely related to each other,forming the structural characteristics of the breeding population,which is the reason for a certain degree of inbreeding in the breeding population.In the autumn and winter after the breeding season,each breeding population cluster moved between various habitats,constantly moving out and adding individuals in the process,resulting in the characteristics of gene mixing in the population,ensuring high genetic diversity and wide gene flow in each breeding population.This pattern of movement and dispersal in non-breeding season is the main reason for the high genetic similarity and lack of spatial genetic structure among patchy breeding populations.