| Sigmella biguttata(Bey-Bienko,1954)belongs to Sigmella,Blattellinae,Ectobiidae,Blaberoidea,Blattodea and Dictyoptera.It lives in the shrubwood or leaf litter,with strong flight ability.They are widely distributed,mainly in Southwest,South and East China.In recent years,some studies have found that there were some minor morphological differences among different geographical populations of Sigmella biguttata,which were treated as intraspecies variation;therefore,we speculated that genetic differentiation might exist in different populations.In order to clarify the existence of genetic differentiation among different geographic populations of Sigmella biguttata,and explore the evolutionary history and the causes of current geographic distribution patterns,we studied the phylogeography of Sigmella biguttata for the first time.In this study,346 samples from 22 geographic populations of Sigmella biguttata were analyzed based on three mitochondrial(COI,COII,ND1)and one nuclear(ITS)genes.The haplotype number,haplotype diversity and nucleotide diversity of the sequences were calculated to analyze the genetic diversity of each gene fragment and population.Complete analysis of molecular variance,the genetic differentiation index was calculated and estimate the gene flow among populations according to the genetic differentiation index Fst,and then determine the degree of genetic differentiation among populations of Sigmella biguttata.The phylogenetic trees were reconstructed using ML and BI methods,and haplotype network diagram was reconstruceted using Median-Joining algorithm,then exploring the phylogenetic relationship of Sigmella biguttata and the origin of the population.The divergence time was estimated based on substitution rate of mitochondrial gene COI;the population historical dynamics was studied by neutrality tests,mismatch distribution analysis and Bayesian Skyline Plot(BSP),and population migration paths were inferred using the Bayesian Stochastic Search Variable Selection(BSSVS)method.Finally,the evolutionary process of the population was explored and the causes of the current geographical distribution patterns was speculated based on the above analysis.The main results as follows:(1)ML and BI trees topology based on the combined dataset were totally consistent,and six groups were clustered together and belongs to four lineages,which was the same as the result of genetic structure analysis using SAMOVA.Lineages I,II and III included only one group,corresponding to Group1,2 and 3,respectively.Lineages I was distributed in Hainan,Lineages II was distributed in Lushan,Jiangxi,and Lineages III was distributed in Hunan,Guangxi,and Guizhou.Lineage IV contained three groups,Group 4,5 and 6.Group5 was recovered as the sister of Group6.Lineage IV was mainly distributed in the Southwest,South and East regions of China.(2)The overall genetic diversity of the population was relatively high(Hd=0.990,?=0.02717),especially Group1(Hd=0.945,?=0.01344),Group5(Hd=0.929,?=0.01065)and Group6(Hd=0.979,?=0.02364).Group1 was located in Hainan with suitable climatic conditions,but Group5 and Group6 were distributed in a wide area(Southwest,South and East China)without significant geographical barriers.Therefore,the frequent gene exchange and suitable habitats in these areas were contributed to the improvement of genetic diversity.The genetic diversity of Group2 and Group4 was relatively low,which was caused by the rapid expansion of the population after the bottleneck effect.(3)The haplotype network diagram analysis showed that there were more mutation steps among each lineage and each group,and there was no shared haplotype among different populations.AMOVA analysis based on mitochondrial,nuclear genes,and combined datasets,respectively,showed more variation among groups.The genetic differentiation index Fst value showed that the minimum Fst value among each group and population were greater than 0.45,and the maximum value of Nm among each group and population were less than 1.All these results indicated that there was significant genetic differentiation among populations of Sigmella biguttata.(4)The population history dynamic detection results showed that Group2,Group3 and Group4 had experienced population expansion,while Group1,Group5 and Group6 had not experienced population expansion.Group2 population expanded after the Last Glacial Maximum,which was the coldest recent period with the lowest global temperature.After the Last Glacial Maximum,the temperature rose and the climate warmed,which promoted the population expansion.Group3 and Group4 populations expanded in the last interglacial period,which was the most recent warming period.The global average annual temperature was 2-5? higher than today,and the climate was relatively warm and humid,which was suitable for the survival,reproduction and spread of Sigmella biguttata,contributing to the rapid population expansion.(5)The population divergence time was estimated based on substitution rate of mitochondrial gene COI,and it showed that the divergence time of each lineage was in the Middle Pleistocene(0.13Ma~0.18Ma).During this period,the expansion of glaciers and the cooling and drying of the climate prompted the divergence within the species,and the separation of Hainan Island from the mainland also led to the differentiation of clade I from the mainland population.The divergence of each group and within the group occurred in the late Pleistocene(0.034Ma~0.12Ma).During this period,the climate alternation between warm-humid and dry-cold,and the complex landforms caused by the uplift of the Qinghai-Tibet Plateau and the surrounding mountains led to the differentiation of geographical populations. |
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